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CIRCUIT IDEAS 5-BAND GRAPHIC EQUALISER R. SUNDAR A KUMAR SOMEN GHOSH bandwidth product greater than 3 plifier. Proper quality factor (Q) needs MHz. The NE5532 or LM833 used in to be selected to avoid overlap in ad- T his equaliser uses low-cost this circuit meets these requirements. jacent bands as this introduces op-amps. Good-quality op- Equaliser circuits typically divide colouration into the audio signal. amps powered by a single volt- the audio spectrum into separate fre- We have used the multiple-feed- age supply are readily available in the quency bands and have independent back bandpass filter topology shown market. The op-amp should have a gain control for each band. The out- in left-most corner at the bottom of the noise density of less than 24nV/√Hz, put of each band is mixed at IC4(A) figure. This is a circuit for single-chan- slew rate of more than 5V/µs and gain- and then fed to an audio power am- nel bandpass filter. If the capacitors are WWW.EFYMAG.COM ELECTRONICS FOR YOU • MAY 2007 • 87 CIRCUIT IDEAS amplifier with a gain of ‘2.’ The input Component Values for 5-band Equaliser signal is divided by ‘2’ by the resistive Centre C Ra Rb Rc Gain (A) Quality (Q) network comprising R3 and R4. Hence frequency (μF) (kilo- (kilo- (kilo- the net gain of this amplifier is unity. fo (Hz) ohms) ohms) ohms) Two 100k resistors (R1 and R2) are 60 C4=C5=0.1 R9=11 R11=27 R10=91 4.1 1.7 used as a voltage divider and the junc- 250 C7=C8=0.1 R14=2.7 R15=6.3 R13=22 4.1 1.7 tion voltage is fed to its 1000 C10=C11=0.047 R18=1.5 R19=3.3 R17=11 3.7 1.6 positive input through R6. This 4000 C13=C14=0.0022 R22=7.5 R23=18 R21=63 4.2 1.7 divider has enough power to feed all 16000 C16=C17=0.0022 R26=2 R27=4.3 R25=15 4.2 1.7 other op-amps directly. Resistor Ro (R8=R12=R16=R20=R24=R28=R30=100Ω) of the same value, the calculations are the octave division, application and has the dual function of noise reduc- fairly simple. For calculating the com- some degree of manufacturers’ prefer- tion and resistive isolation of capaci- ponent values, use the following for- ence, but nearly all share the basic oc- tive load. It may be varied between 50 mulae: tave boundaries that are based on a and 150 ohms depending on the noise Centre frequency (fo) : 1/2πC√(Ra||Rb)Rc centre frequency of 1000 Hz. in the circuit. Bandwidth (B) : 1/πCRc A balance between the number of The potmeters (VR1 through VR5) Quality factor (Q) : fo/B = πfoCRc filters and bandwidth need to be ob- are in the signal path and hence should Gain (A) : –Rc/2Ra served. It is possible to use a wider be of the best quality possible. Wrap These can be combined to give the bandwidth and fewer filters, or nar- the body of the pots with bare copper following formulae: rower bandwidth and more filters. wire and solder the other end of the Ra = Q/2πfoAC Anything narrower than 1/3 octave is wire to ground. Since the filters are Rb = Q/2πfoC (2Q2–A) rare, since the complexity of the filters very sensitive, all resistances should Rc = Q/πfoC increases for higher values of ‘Q.’ This be metal-film type and the capacitors Begin the calculations by choosing can get rather expensive and in reality should be polyester type. a large value of capacitance (~0.1F) and is of limited use for most applications Each stage of the op-amp needs to smaller value of resistances. Increasing in audio systems. be capacitively coupled to the next the capacitance decreases resistances National Semiconductor lists the stage so that the DC does not get (Ra, Rb and Rc). Care must be taken to following mid-frequencies for a 10- propagated and amplified. For a good avoid overloading on the input buffer band graphic equaliser: 32, 64, 125, 250, low-frequency response, this coupling op-amp. Note that stray capacitances 500, 1k, 2k, 4k, 8k and 16k. It also rec- capacitor should be greater than 1 µF. on the board reduces the value of ‘C.’ ommends a ‘Q’ of 1.7 for equalisers. A 10µF, 16V capacitor is used in each The bandwidth and gain do not de- The table lists the component val- stage of the circuit here. pend on Rb. Hence, Rb can be used to ues for different centre frequencies of The circuit is powered by a 12V modify the mid-frequency without af- the equaliser. We used ‘Q’ of 1.7 and DC regulated supply. A well-regulated fecting the bandwidth and gain. gain (A) of 4. supply using 7812 is recommended. For equalisers, there are standard The circuit for the 5-band equaliser Ground the Vcc pin of each op-amp mid-frequencies that are normally uses IC1 (A) LM833 as the buffer stage with a 0.1µF ceramic disk capacitor to used. The exact frequencies depend on for the equaliser. It is a non-inverting bypass the noise. 88 • MAY 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM CIRCUIT IDEAS ANTI-COLLISION REAR LIGHT S.C. DW IVEDI ASHOK K. DOCTOR NAND schmitt trigger CD4093, 8-stage of LEDs flash one by one. shift-and-store bus register CD4094 All the LEDs will then glow for D uring poor visibility, i.e., and some descrete components. some time and switch off for some when there is fog, or at dawn An oscillator is built around gate A, time, and the cycle will repeat. Input or dusk, or when your ve- whose frequency can be varied through pins 12 and 13 of the unused gate D hicle gets stalled on a lonely stretch of preset VR1 when required. The output must be tied to ground and pin 11 left a highway, this flashing light will pro- of the oscillator is fed to IC1 and IC3. open. Preset VR1 should be of cermet vide safety and attract the attention of When the circuit is switched on, the type and used to change the flashing people to help you out. It uses high- oscillator starts oscillating, the counter rate of each group of LEDs. brightness yellow LEDs. starts counting through IC1 and the The circuit works off regulated The circuit uses a dual binary data is shifted on positive-going clock 12V. Assemble it on a general-purpose counter CD4520, quadruple 2-input through IC3. As a result, the four groups PCB and house suitably. WWW.EFYMAG.COM ELECTRONICS FOR YOU • JUNE 2007 • 83 circuit ideas antiSleep alarm for StudentS SureSh Kumar K.B. BC547, relay RL1 and buzzer. The Schmitt-trigger NAND gate T edi his circuit saves both time and (IC1) is configured as an astable multi- s.c. dwiv electricity for students. It helps vibrator to generate clock for the timer to prevent them from dozing (IC2). The time period can be calcu- off while studying, by sounding a beep lated as T=1.38×R×C. If R=R1+VR1=15 at a fixed time interval, say, 30 minutes. kilo-ohms and C=C2=10 µF, you’ll get D3, further counting stops and relay If the student is awake during the beep, ‘T’ as 0.21 second. Timer IC CD4020 RL1 energises to deactivate all the ap- he can reset the circuit to beep in the (IC2) is a 14-stage ripple counter. pliances. This state changes only when next 30 minutes. If the timer is not reset Around half an hour after the reset IC1 is reset by pressing switch S1. during this time, it means the student of IC1, transistors T1, T2 and T3 drive Assemble the circuit on a general- is in deep sleep or not in the room, and the buzzer to sound an intermediate purpose PCB and enclose it in a suit- the circuit switches off the light and fan beep. If IC2 is not reset through S1 able cabinet. Mount switch S1 and the in the room, thus preventing the wast- at that time, around one minute later buzzer on the front panel and the relay age of electricity. the output of gate N4 goes high and at the back side of the box. Place the The circuit is built around Schmitt- transistor T4 conducts. As the output 12V battery in the cabinet for powering trigger NAND gate IC CD4093 (IC1), of gate N4 is connected to the clock the circuit. In place of the battery, you timer IC CD4020 (IC2), transistors input (pin 10) of IC2 through diode can also use a 12V DC adaptor. 9 8 • M a r c h 2 0 1 0 • e l e c t ro n i c s f o r yo u w w w. e f y M ag . co M circuit ideas The output from IC1 is fed to display driver LM3915 (IC2) through aquariuM Probe s.c. dwiv edi preset VR3 (50-kilo-ohm). With careful adjustments, the wiper of VR3 can provide 0-400 millivolts to the input of IC2. The highly sensi- D. Mohan KuMar temperature, the diode generates 2mV tive input of IC2 accepts as low as output voltage. That is, at 5°C, it is 10 50 mV if the reference voltage at its A number of environmental mV, which rises to 70 mV when the pin 7 is adjusted using a variable factors including light and temperature is 35°C. This property resistor. To increase the sensitivity temperature affect fish culture. is exploited in the circuit to sense the of IC2, preset VR4 is connected at The temperature of water has profound temperature variation in aquarium one end to ‘reference voltage end’ effect because fish cannot breed above water. Fig. 1 shows the circuit diagram pin 7 and its wiper is connected to or below the critical temperature lim- of the aquarium probe. ‘high end’ pin 6 of the internal resis- its. Temperature between 24°C and Since the output from the diode tor chain. 33°C is found to be the best to induce sensor is too low, a high-gain invert- When approximately 70 mV is spawning in fishes. This particular ing DC amplifier is used to amplify provided to the input of IC2 by adjust- temperature range is also necessary the voltage. CA3140 (IC1) is the CMOS ing preset VR3, LED1 (green) lights for the healthy growth of nursery fish version op-amp that can operate down up to indicate that the temperature is fries (young fishes). Rise of water tem- to zero-volt output. The highest output approximately 35°C, which is the cross- perature due to sunlight may adversely available from IC1 is 2.25V less than ing point. When the input receives 100 affect the fish rearing process. the input voltage at pin 7. With resistor mV, LED2 (red) lights up to indicate approximately 50°C. Finally, the buzzer starts beeping if the input receives 130 mV corresponding to a temperature of 65°C. In short, LEDs and the buzzer re- main standby when the temperature of the water is below 35°C (normal). With each step increase of 30 mV in the input (cor- responding to 15°C rise in temperature), LEDs and the buzzer become active. Fig. 1: Circuit for aquarium probe Pin 16 of IC2 is used to drive the pi- The circuit of aquatic probe de- R4 and ezobuzzer through transistor T1. When scribed here can monitor the tem- VR2, the pin 16 of IC2 becomes low, T1 conducts perature of water and indicate the variation to beep the piezobuzzer. Resistor R7 rise in temperature through audio- in diode keeps the base of transistor T1 high to visual indicators. A readily available Fig. 2: Diode sensor assembly voltage avoid false alarm. IC4 provides regu- signal diode 1N34 is used in the can be lated 9V DC to the circuit. circuit as the temperature sensing amplified to the required level. Resis- Assemble the circuit on a common probe. The resistance of the diode tor R1 restricts current flow through PCB and enclose in a suitable case. depends on the temperature in its diode D1 and preset VR1 (1-kilo-ohm) Glass signal diode D1 is immersed vicinity. sets the input voltage at pin 3. IC3 in water to sense the temperature Typically, the diode can gener- (7805) provides regulated 5 volts to the of water. Its leads should be coated ate around 600 mV when a potential inputs of IC1, so that the input voltage with enamel paint to avoid shorting difference is applied to its terminals. is stable for accurate measurement of in water. Alternatively, enclose the For each degree centigrade rise in temperature. diode in a small glass tube or test 9 2 • j u ly 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m circuit ideas tube having sufficient internal space mV, so that the input of IC2 (pin 5) hot water. Now red LED2 will glow. to fit the diode as shown in Fig. 2. receives 70 mV corresponding to the At this position, the voltage at pin 6 Make the sensor assembly waterproof diode output voltage at 35°C. At this of IC1 will be around 100 mV. When using wax. stage, green LED1 should turn on. the temperature of water increases Take care while calibrating and If it doesn’t, adjust VR4 until LED1 further to 65°C, the buzzer starts setting the circuit. With 5V DC sup- just lights up. Immerse the diode beeping. After calibration, immerse ply to diode D1 and an ambient tem- in temperature-adjusted hot water the diode assembly in the aquarium perature of about 35°C, D1 generates (35°C) and adjust VR3 and VR4 until tank just below the water surface around 70 mV. Adjust VR3 until the green LED1 lights up. Increase the and fix it permanently to avoid float- voltage in its wiper increases to 70 water temperature to 50°C by adding ing. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • j u ly 2 0 0 8 • 9 3 circuit ideas automated alarm CirCuitS s.c. dwiv edi Pallabi Sarkar and Normally, when the door is closed, anirban SenguPta reed switch S1 is closed, transistor T1 conducts and the monostable multivi- When the door is opened, reed T wo alarm circuits are presented brator (IC1) remains in standby mode switch S1 gets disconnected, T1 stops here. One produces bird-chirp- with ‘low’ output at pin 10. conducting and low-to-high pulse at pin ing sound and the other British police siren tone. Fig. 1 shows the circuit of the bird- chirping-sound alarm unit along with the circuit of the control unit. Fig. 2 shows the circuit of only the British police siren tone generator, which has to be integrated with the control circuit portion of Fig. 1 at points A and B to complete the circuit diagram of auto- mated alarm. The control unit is built around ICs CD4047 and CD4027 (as shown on the left side of the dotted line in Fig. 1). As mentioned earlier, it is common to both the alarm circuits. IC CD4047 (IC1) is wired in positive-edge-triggering monostable multivibrator mode to set and reset IC CD4027 (IC2). The output pulse width of IC1 depends on the values of capacitor C2 and resistor R3 connected to its pins 1, 2 and 3. Fig. 2: Alarm circuit that generates police siren tone Fig. 1: Alarm circuit that generates bird-chirping sound 9 6 • F e b r ua ry 2 0 0 9 • e l e c t ro n i c s f o r yo u w w w. e F y m ag . co m circuit ideas 8 of IC1 triggers the monostable and a T2 (BC548), which enables the alarm ing sound. short-duration positive pulse of about circuit. For the chirping-sound alarm gen- 10 seconds is available as Q output at The output at point A is used to erator, assemble the circuit shown in pin 10. At the same time, complementary enable the alarm tone generator circuit Fig. 1 on a separate general-purpose output Q goes low at pin 11. The output (on the right side of the dotted line) PCB and enclose in a small box. And if from IC1 is used to set and reset IC2. consisting of two 555 timer ICs marked you want an alarm circuit with British IC2 is a low-power, dual J-K mas- as IC3 and IC4. The R-C network de- police siren tone, assemble the circuit ter/slave flip-flop having independ- termines the frequency of the sound shown in Fig. 2 on another general- ent J, K, set, reset and clock inputs. produced. The triangular waveform purpose PCB and connect it to points The flip-flops change states on the of the astable multivibrator is taken A and B of the control unit shown in positive-going transition of the clock out from the junction of pins 2 and Fig. 1 after removing the circuit on the pulses. IC2 is wired such that its Q 6 of IC3. This waveform is fed as the right side of the dotted line. Use a 9V, output turns ‘high’ when reset pin 4 control voltage at pin 5 of IC4 through 500mA standard adaptor to power the receives a high pulse. When set pin 7 resistor R18. The output received from circuit. receives a high pulse, Q output goes pin 3 of IC4 is fed to the base of transis- This circuit may be used as a secu- low and Q output goes high. This tor T3 to drive an 8-ohm loudspeaker rity alarm in banks, households and lights up LED2 and drives transistor (LS1), which generates the bird-chirp- motorcars. w w w. e F y m ag . co m e l e c t ro n i c s f o r yo u • F e b r ua ry 2 0 0 9 • 9 7 circuit ideas autoMatiC light Controller s.c. dwiv edi using 7806 M.K. Chandra Mouleeswaran of the transistor. In this way, the volt- Normally, the resistance of LDR1 age regulator is able to operate a light is low during daytime and high dur- V oltage regulator ICs (78xx se- bulb automatically as per the ambient ing nighttime. During daytime, when ries) provide a steady output light. light falls on LDR1, pnp transistor T1 voltage, as against a widely To derive the power supply for conducts. The common terminal of IC1 fluctuating input supply, when the the circuit, the 50Hz, 230V AC mains connects to the ground and IC1 outputs common terminal is grounded. Any is stepped down by transformer X1 6V. As a result, transistor T2 does not voltage about zero volt (ground) con- to deliver a secondary output of 12V, conduct and the relay remains de-en- nected in the common terminal is add- 250 mA. The secondary output of the ergised. The light bulb remains ‘off’ as ed to the output voltage. That means transformer is applied to a bridge rec- the mains connection is not completed the increase in the common terminal tifier comprising diodes D1 through through the relay contacts. voltage is reflected at the output. On D4, filtered by capacitor C1 and fed During nighttime, when no light the other hand, if the common terminal to the input terminal of the regulator falls on LDR1, it offers a high resist- is disconnected from the ground, the (IC1). ance at the base junction of transistor full input voltage is available at the The common terminal (pin 2) of IC1 T1. So the bias is greatly reduced and output. is connected to the ground line of the T1 doesn’t conduct. Effectively, this This characteristic is utilised in the circuit through transistor BC557 (T1). removes the common terminal of IC1 present circuit. When the common The transistor is biased by R2, R3, VR1 from ground and it directs the full terminal is connected to the ground, and LDR1. The grounding of IC1 is input DC to the output. Transistor T2 the regulator output is equivalent to controlled by transistor T1, while light conducts and the relay energises to the rated voltage, and as soon as the is sensed by LDR1. Using preset VR1, light up the bulb as mains connection terminal is disconnected from the you can adjust the light-sensing level completes through the relay contacts. ground, the output increases up to the of transistor T1. As LDR1 is in parallel to VR1+R3 input voltage. The output of IC1 is fed to the base combination, it effectively applies The common terminal is control- of transistor T2 (through resistor R4 only half of the total resistance of led by a transistor, which works as a and zener diode ZD1) and relay RL1. the network formed by R3, VR1 and switch on the terminal. For automatic LED1 connected across the positive LDR1 to the junction at T1 in total control of light, a light-dependent re- and ground supply lines acts as a darkness. In bright light, it greatly sistor (LDR1) is connected to the base power-‘on’ indicator. reduces the total effective resistance at the junction. The circuit is simple and can be assembled on a small general-purpose PCB. Use a heat-sink for IC1. Make sure that LDR1 and the light bulb are well separated. The circuit can be used for streetlights, tubelights or any other home electri- cal lighting system that needs to be au- tomated. 9 2 • A p r i l 2 0 1 0 • e l e c t ro n i c s f o r yo u w w w. e f y m Ag . co m CIRCUIT IDEAS AUTOMATIC PHASE CHANGER S.C. DW IVEDI MUHAMMAD AJMAL P. The mains power supply phase R is stepped down by transformer X1 to I n three-phase applications, if low deliver 12V, 300 mA, which is recti- As soon as phase-R voltage goes voltage is available in any one or fied by diode D1 and filtered by ca- below 200V, the voltage at inverting two phases, and you want your pacitor C1 to produce the operating pin 2 of IC1 goes below reference volt- equipment to work on normal voltage, voltage for the operational amplifier age of 5.1V, and its output goes low. this circuit will solve your problem. (IC1). The voltage at inverting pin 2 of As a result, transistor T1 conducts and However, a proper-rating fuse needs oprational amplifier IC1 is taken from relay RL1 energises and load L1 is to be used in the input lines (R, Y and the voltage divider circuit of resistor disconnected from phase ‘R’ and B) of each phase. The circuit provides R1 and preset resistor VR1. VR1 is used connected to phase ‘Y’ through relay correct voltage in the same power sup- to set the reference voltage according RL2. ply lines through relays from the other to the requirement. The reference volt- Similarly, the auto phase-change of phase where correct voltage is avail- age at non-inverting pin 3 is fixed to the remaining two phases, viz, phase able. Using it you can operate all your 5.1V through zener diode ZD1. ‘Y’ and phase ‘B,’ can be explained. equipment even when correct voltage Till the supply voltage available in Switch S1 is mains power ‘on’/’off’ is available on a single phase in the phase R is in the range of 200V-230V, switch. building. the voltage at inverting pin 2 of IC1 Use relay contacts of proper rating The circuit is built around a trans- remains high, i.e., more than reference and fuses should be able to take-on former, comparator, transistor and re- voltage of 5.1V, and its output pin 6 the load when transferred from other lay. Three identical sets of this circuit, also remains high. As a result, transis- phases. While wiring, assembly and in- one each for three phases, are used. tor T1 does not conduct, relay RL1 re- stallation of the circuit, make sure that Let us now consider the working of mains de-energised and phase ‘R’ sup- you: the circuit connecting red cable (call it plies power to load L1 via normally- 1. Use good-quality, multi-strand ‘R’ phase). closed (N/C) contact of relay RL1. insulated copper wire suitable for your WWW.EFYMAG.COM ELECTRONICS FOR YOU • JULY 2007 • 93 CIRCUIT IDEAS current requirement. nections from mains. 2. If the input voltage is low in two 2. Use good-quality relays with EFY Note: 1. During testing in the phases, loads L1 and L2 may also be proper contact and current rating. lab, we used a 12V, 200-ohm, single- connected to the third phase. In that 3. Mount the transformer(s) and re- phase changeover relay with 6A cur- situation, a high-rating fuse will be re- lays on a suitable cabinet. Use a Tag rent rating. Similarly, ampere-rated quired at the input of the third phase Block (TB) for incoming/outgoing con- fuses were used. which is taking the total load. 94 • JULY 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM circuit ideas Constant-Current s.c. dwiv edi Battery Charger Monoj Das 13.5-14.2V in the case of a 12V battery), 14+5=19V. give indication and the charger will For the sake of simplicity, this con- T here are many ways of battery switch off automatically. You need not stant-current battery charger circuit is charging but constant-current remove the battery from the circuit. divided into three sections: constant- charging, in particular, is a 4. If the battery is discharged be- current source, overcharge protection popular method for lead-acid and Ni- low a limit, it will give deep-discharge and deep-discharge protection sec- Cd batteries. In this circuit, the battery indication. tions. is charged with a constant current that 5. Quiescent current is less than 5 The constant-current source is is generally one-tenth of the battery mA and mostly due to zeners. built around MOSFET T5, transistor capacity in ampere-hours. So for a 6. DC source voltage (VCC) ranges T1, diodes D1 and D2, resistors R1, R2, 4.5Ah battery, constant charging cur- from 9V to 24V. R10 and R11, and potmeter VR1. Diode rent would be 450 mA. 7. The charger is short-circuit pro- D2 is a low-temperature-coefficient, This battery charger has the follow- tected. highly stable reference diode LM236-5. ing features: D1 is a low-forward-drop schottky LM336-5 can also be used with reduced 1. It can charge 6V, 9V and 12V bat- diode SB560 having peak reverse volt- operating temperature range of 0 to teries. Batteries rated at other voltages age (PRV) of 60V at 5A or a 1N5822 +70°C. Gate-source voltage (VGS) of T5 can be charged by changing the values diode having 40V PRV at 3A. Nor- is set by adjusting VR1 slightly above of zener diodes ZD1 and ZD2. mally, the minimum DC source volt- 4V. By setting VGS, charging current 2. Constant current can be set as age should be ‘D1 drop+Full charged can be fixed depending on the battery per the battery capacity by using a battery voltage+VDSS+ R2 drop,’ which capacity. First, decide the charging potmeter and multimeter in series with is approximately ‘Full charged battery current (one-tenth of the battery’s Ah the battery. voltage+5V.’ For example, if we take capacity) and then calculate the nearest 3. Once the battery is fully charged, full-charge voltage as 14V for a 12V standard value of R2 as follows: it will attain certain voltage level (e.g. battery, the source voltage should be R2 = 0.7/Safe fault current 1 1 4 • Au g u s t 2 0 0 9 • e l e c t ro n i c s f o r yo u w w w. e f y m Ag . co m circuit ideas R2 and T1 limit the charging cur- diode ZD1 starts conducting after LED2 will glow to indicate that the bat- rent if something fails or battery termi- its breakdown voltage is reached, tery voltage is low. nals get short-circuited accidentally. i.e., it conducts when the battery Values of zener diodes ZD1 and To set a charging current, while voltage goes beyond a prefixed high ZD2 will be the same for 6V, 9V and a multimeter is connected in series level. Adjust VR2 when the battery 12V batteries. For other voltages, you with the battery and source supply is is fully charged (say, 13.5V in case of need to suitably change the values of present, adjust potmeter VR1 slowly a 12V battery) so that VGS of T5 is set ZD1 and ZD2. Charging current pro- until the charging current reaches its to zero and hence charging current vided by this circuit is 1 mA to 1 A, and required value. stops flowing to the battery. LED1 no heat-sink is required for T5. If the Overcharge and deep-discharge glows to indicate that the battery is maximum charging current required is protection have been shown in dotted fully charged. When LED1 glows, the 5A, put another LM236-5 in series with areas of the circuit diagram. All com- internal LED of the optocoupler also diode D2, change the value of R11 to 1 ponents in these areas are subjected to glows and the internal transistor con- kilo-ohm, replace D1 with two SB560 a maximum of the battery voltage and ducts. As a result, gate-source voltage devices in parallel and provide a good not the DC source voltage. This makes (VGS) of MOSFET T5 becomes zero and heat-sink for MOSFET T1. TO-220 pack- the circuit work under a wide range of charging stops. age of IRF540 can handle up to 50W. source voltages and without any influ- Normally, zener diode ZD2 con- Assemble the circuit on a gen- ence from the charging current value. ducts to drive transistor T3 into con- eral-purpose PCB and enclose in a Set overcharge and deep-discharge duction and thus make transistor T4 box after setting the charging current, voltage of the battery using potmeters cut-off. If the battery terminal voltage overcharge voltage and deep-discharge VR1 and VR2 before charging the bat- drops to, say, 11V in case of a 12V bat- voltage. Mount potmeters VR1, VR2 tery. tery, adjust potmeter VR3 such that and VR3 on the front panel of the In overcharge protection, zener transistor T3 is cut-off and T4 conducts. box. w w w. e f y m Ag . co m e l e c t ro n i c s f o r yo u • Au g u s t 2 0 0 9 • 1 1 5 circuit ideas BAttery-level indicAtor edi s.c. dwiv Aniruddh K.S. makes it easier to recognise the voltage level on the basis of the N ormally, in mobile phones, calibration made. Red LEDs (LED1 the battery level is shown in through LED3) indicate battery initially set it at 3V. Slowly adjust VR1 dot or bar form. This lets you capacity of less than 40 per cent. until LED1 glows. Now, increase the easily recognise the battery level. Here Orange LEDs (LED4 through LED6) input voltage to 15V in steps of 1.2V we present a circuit that lets you know indicate battery capacity of 40 to until the corresponding LED (LED2 the battery level of a device from the less than 70 per cent and green through LED10) lights up. number of LEDs that are glowing. It LEDs (LED7 through LED10) indi- Now the circuit is ready to show uses ten LEDs in all. So if three LEDs cate battery capacity of 70 to under any voltage value with respect to the glow, it indicates battery capacity of 100 per cent. The brightness of the maximum voltage. As the number of 30 per cent. Unlike in mobile phones LEDs can be adjusted by varying the LEDs is ten, we can easily consider one where the battery-level indicator func- value of preset VR2 between pins 6 LED for 10 per cent of the maximum tion is integrated with other functions, and 7. voltage. here only one comparator IC (LM3914) Diode D1 prevents the circuit Connect the voltage from any does it all. from reverse-polarity battery con- battery to be tested at the input The LM3914 uses ten comparators, nection. The tenth LED glows only probes of the circuit. By examining which are internally assembled in the when the battery capacity is full, the number of LEDs glowing you voltage divider network based on the i.e., the battery is fully charged. can easily know the status of the bat- current-division rule. So it divides the When the battery is fully charged, tery. Suppose five LEDs are glowing. battery level into ten parts. relay-driver transistor T1 conducts In this case, the battery capacity is The circuit derives the power to energise relay RL1. This stops the 50 to 59 per cent of its maximum supply for its operation from the charging through normally-open value. battery of the device itself. It uses (N/O) contacts of relay RL1. Assemble the circuit on a general- ten LEDs wired in a 10-dot mode. For calibration, connect 15V vari- purpose PCB. Calibrate it and then en- The use of different coloured LEDs able, regulated power supply and close in a box. 8 4 • D E C E m b E r 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. E f y m ag . Co m circuit ideas Bicycle indicaTor edi s.c. dwiv T.K. Hareendran the square-wave oscillators (one built around T1 and T2 and the other built T he electronic bicycle signaling around T3 and T4) drive four red LEDs unit described here uses low- (LED1 and LED2, and LED5 and LED6, determined by timing capacitors C1 cost components and is a good respectively), which blink to indicate and C2. Resistors R2 and R3 limit the operating current of LEDs (LED1 and LED2). At the same time, the green LED (LED3) starts glowing to indicate the present direction status. Similar action happens in the next oscillator circuit built around transistors T3 and T4 when switch S2 is flipped to ‘on’ position. Indi- cators at the front right (FR) and rear right (RR) start blinking, and at the same time the green LED (LED4) glows to indicate the direc- tion status. Switch S3 is used for emergency indication. When it is flipped to ‘on’ position, both the oscillators get power supply through diodes D1 and D2. As a result, LED1 through Fig. 1: Circuit of bi-cycle indicator LED6 start working simultaneous- ly. In this condition, all the LEDs blink, except LED3 and LED4, which glow steadily. After assembling the circuit on a general- purpose PCB, enclose it in a suitable cabinet as shown in Fig. 2 and mount on the handle bar of the bicycle, pref- Fig. 3: Suggested enclosure (indicators) erably at the mechani- cal centre point. Con- the direction of turn. Ad- nect switch S1 at the left-hand side, S2 ditional steady-glow LEDs at the right-hand side and emergency (LED3 and LED4) are in- switch S3 in the middle of the master corporated to indicate the unit. Now place this master unit at Fig. 2: Suggested enclosure (master unit) working status. the top of the handle bar and do the substitute to many commercially avail- The working of the cir- essential interconnections using flex- able versions. It works in an extremely cuit is straightforward. When ible wires. Connect the front indica- different manner and is convenient to switch S1 is flipped to ‘on’ po- tors (LED1 and LED5) to the left and operate. sition, DC supply from right side of the handle and similarly The circuit works off a 9V PP3 the battery is extended to the oscil- rear indicators (LED2 and LED6) can (alkaline-type) battery and is basically lator circuit formed by transistors be mounted in the carrier frame of a set of two independent free-running T1 and T2. Now the left-side oscil- the bicycle. For the direction indica- oscillators (astable multivibrators) built lator starts oscillating and the visual tor, you can use the symbol shown in around four low-power transistors indicators at the front left (FL) and Fig. 3 and place it at the centre of the and a few passive components. Both rear left (RL) start blinking at a rate handle. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • j u ly 2 0 0 8 • 9 5 blown fuse indicator G enerally, when an equipment in- second arm it is only 2V. So current flows (see Fig. 2). An optocoupler is used to dicates no power, the cause may through the second arm, i.e. through the trigger the siren. When the fuse blows, red be just a blown fuse. Here is a green LED, causing it to glow; whereas LED glows. Simultaneously it switches circuit that shows the condition of fuse the red LED remains off. ‘on’ the siren. through LEDs. This compact circuit is When the fuse blows off, the supply In place of a bicolour LED, two LEDs very useful and reliable. It uses very few to green LED gets blocked, and because of red and green colour can be used. components, which makes it inexpensive only one LED is in the circuit, the red LED Similarly, only one diode in place of D1 too. glows. In case of power failure, both LEDs and D2 may be used. Two diodes are used Under normal conditions (when fuse remain ‘off’. to increase the voltage drop, since the is alright), voltage drop in first arm This circuit can be easily modified to two LEDs may produce different voltage is 2V + (2 x 0.7V) = 3.4V, whereas in produce a siren in fuse-blown condition drops. 12 ELECTRONICS PROJECTS Vol. 22 circuit ideas Car anTi-THefT Guard s.c. dwiv edi T.K. Hareendran tor R1, which prevents transistor T1 from conducting. In this position, anti- H ere is an easy-to-build car theft guard cir- anti-theft guard. The circuit, cuit is in sleep shown in Fig. 1, is simple and mode. easy to understand. When key-oper- W h e n ated switch S2 of the car is turned on, someone opens 12V DC supply from the car battery is the car door, extended to the entire circuit through switch S1 be- polarity-guard diode D5. Blinking comes ‘off’ as LED1 flashes to indicate that the guard shown in Fig. circuit is enabled. It works off 12V 2. As a result, power supply along with current-limit- transistor T1 ing resistor R4 in series. conducts to fire When the car door is closed, door r e l a y - d r i v e r Fig. 2: Wiring diagram for door switch (S1) switch S1 is in ‘on’ position and 12V SCR1 (BT169) power supply is available across resis- after a short delay introduced by ca- pacitor C1. Electromagnetic relay RL1 energises and its N/O contact connects the power supply to pi- ezobuzzer PZ1, which starts sounding to in- dicate that someone is trying to steal your car. To reset the circuit, turn off switch S2 using car key. This will cut- off the power supply to the circuit and stop the buzzer sound. Assemble the cir- cuit on a general-pur- pose PCB and house in a small box. Con- nect switch S1 to the car door and keep pi- ezobuzzer PZ1 at an appropriate place in Fig. 1: Circuit of car anti-theft guard the car. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • m ay 2 0 0 8 • 7 5 CIRCUIT IDEAS via switch S1. IVEDI The circuit works off a 9V bat- S.C. DW CLOCK TIMER tery. Assemble it on a general-pur- pose PCB and enclose in a suitable cabinet. Provide an AC outlet in the D. MOHAN KUMAR set VR1. The inverting and non-invert- cabinet to switch on the appliance us- ing inputs of LM311 are different from ing the circuit. As mentioned earlier, W ith this simple clock- other op-amps and it outputs sink cur- the input signal is obtained from the controlled timer, you will rent through pin 7 or source current buzzer terminals of the clock. Remove never again miss your through pin 1. the small buzzer of the clock and con- favourite TV or radio programme. The When pin 3 of IC1 is at a higher nect point ‘A’ to the positive termi- TV or radio will switch on automati- voltage than pin 2, its output sinks nal and point ‘B’ to the negative ter- cally at the time preset by you and as indicated by LED1. This gives a minal of the buzzer. Connect the will remain ‘on’ until the power sup- short negative pulse to the monostable mains AC terminal outlet to the nor- ply fails or is disconnected. wired around timer NE555. Resistor mally-opened (N/O) contact of relay The circuit uses the AC signals gen- R5 keeps trigger pin 2 of IC2 high. RL1. So when the relay energises, erated at the buzzer terminals of an The short-interval monostable outputs 230V AC operates the connected ap- alarm clock. The AC signals are am- a high signal for a brief period to the pliance. plified by transistors T1 and T2 and gate of SCR1 (BT169) and relay RL1 Set the desired time in the clock by the amplified output from the emitter energises. The latching action of SCR1 adjusting the alarm set-up and switch of T2 is fed to the inverting input of keeps the relay pulled even when the on the circuit. When the set time negative-voltage comparator IC LM311 output of the monostable turns low. reaches, the appliance will switch on (IC1). The non-inverting input of IC1 The relay can be de-energised by dis- automatically. The circuit can also be gets a presettable voltage through pre- connecting the supply to the circuit connected to digital clocks. 96 • FEBRUARY 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM CIRCUIT IDEAS CURRENT SENSOR S.C. DW IVEDI D. MOHAN KUMAR transistors in the input to provide very high input impedance (1.5 T-ohms), H igh-wattage appliances like very low input current (10 pA) and by feeding Q9 output to the electric irons, ovens and heat- high-speed switching performance. piezobuzzer for aural alarm through ers result in unnecessary The inverting input of IC1 is pre- the intermediate circuitry. Resistors R5 power loss if left ‘on’ for hours unno- set with VR1. In the standby mode, and R6 along with capacitor C1 main- ticed. Here is a circuit that senses the the primary of the transformer accepts tain the oscillations in IC2 as indicated flow of current through the appliances e.m.f. from the instrument or sur- by blinking LED1. The high output and gives audible beeps every fifteen rounding atmosphere, which results in from IC2 is used to activate a simple minutes to remind you of power-’on’ low-voltage input to IC1. This low oscillator comprising transistors T2 status. voltage at the non-inverting input and T3, resistors R8 and R10, and ca- This is a non-contact version of cur- keeps the output of IC1 low. Thus tran- pacitor C2. rent monitor and can sense the flow sistor T1 doesn’t conduct and pin 12 When the Q9 output of IC2 be- of current in high-current appliances of IC2 goes high to disable IC2. As a comes high, zener diode ZD1 provides from a distance of up to 30 cm . It uses result, the remaining part of the cir- 3.1 volts to the base of transitor T2. a standard step-down transformer (0- cuit gets inactivated. Since transistor T2 is biased by a high- 9V, 500mA) as the current sensor. Its When a high-current appliance is value resistor (R8), it will not conduct secondary winding is left open, while switched on, there will be a current immediately. Capacitor C2 slowly the primary winding ends are used to drain in the primary of the transformer charges and when the voltage at the detect the current. The primary ends to the negative rail due to an increase base of T2 increases above 0.6 volt, it of the transformer are connected to a in the e.m.f. caused by the flow of cur- conducts. When T2 conducts, the base full-wave bridge rectifier comprising rent through the appliance. This results of T3 turns low and it also conducts. diodes D1 through D4. The rectified in voltage rise at the non-inverting in- The piezobuzzer connected to the col- output is connected to the non-invert- put and the output of IC1 becomes high. lector of T3 gives a short beep as ca- ing input of IC CA3140 (IC1). This high output drives transistor T1 pacitor C2 discharges. This sequence IC CA3140 is a 4.5MHz BIMOS op- into conduction and the reset pin of of IC2 output at Q9 becoming high and erational amplifier with MOSFET in- IC2 becomes low, which enables IC2. conduction of transistors T2 and T3 re- put and bipolar transistor output. It IC CD4060 (IC2) is a 14-stage ripple sulting in beep sound repeats at short has gate-protected MOSFET (PMOS) counter. It is used as a 15-minute timer intervals. 94 • DECEMBER 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM DARKROOM TIMER T he timer circuit described here pro- built around transistor T2, turning it on sistor T2 is coupled to a small speaker vides a pleasant musical tone in and off. As capacitor C1 is charged through a transistor-radio type output your darkroom at 1-second inter- through preset VR1 and resistor R1, the transformer. vals. The circuit takes up very little space emitter voltage of UJT rises toward the The 22-kilo-ohm value of resistor R3 and can be easily converted into a metro- supply voltage. represents a compromise between tone nome. When the emitter voltage becomes suf- duration and intensity. You can use re- Unijunction transistor (UJT) T1 func- ficiently positive, the emitter becomes for- sistors having a value anywhere between tioning as a relaxation oscillator triggers ward biased and discharges capacitor C1 10 kilo-ohms and 25 kilo-ohms for differ- the phase-shift audio oscillator circuit through the emitter-base 1 (B1) junction ent durations and intensities of the out- and resistor R2. put signals. The voltage drop Since the unijunction transistor is across R2 forward functioning as the oscillator trigger, biases transistor changing the values of one or more com- T2 and turns it on. ponents in the UJT circuit will change As capacitor C1 the rate of the tone burst. The tone fre- becomes dis- quency can be varied by changing the charged, the cur- value of any or more of capacitors C2 rent through re- through C4 and resistors R5 and R6 in sistor R2 drops the phase-shift network. and transistor T2 The primary winding of transformer is cut off. X1 can be tuned for a slight increase in A tone signal the output, using capacitor values between is generated by 0.05 and 0.25 μF for C5 by trial-and-error transistor T2 and method. Tone pulses should begin about R-C coupled ten seconds after the unit is turned on. phase-shift oscilla- After a minute or so, adjust preset VR1 tor. Part of the sig- for 1-second beats by comparing the tim- nal taken from the ing of the beats with the seconds needle collector of tran- on your wristwatch. 174 ELECTRONICS PROJECTS Vol. 22 CIRCUIT IDEAS DESKTOP POWER SUPPLY S.C. DW IVEDI T.K. HAREENDRAN top power supply. Regulator IC LM317T tive load is U seful for electronics hobbyists, is arranged in its stan- connected at this linear workbench power dard application. Di- the output. supply converts a high input ode D1 guards against Similarly, ca- voltage (12V) from the SMPS of a PC polarity reversal and pacitor C3 sup- into low output voltage (1.25 to 9 capacitor C1 is an ad- presses any re- volts). An adjustable three-pin voltage ditional buffer. The sidual ripple. regulator chip LM317T (IC1) is used green LED (LED1) in- Connect a Fig. 3: Suggested power here to provide the required voltages. Fig. 2: Pin dicates the status of the configuration of standard digi- supply box The LM317T regulator, in TO-220 pack, LM317 power input. Diode D2 tal voltmeter in can handle current of up to 1 amp in prevents the output parallel with the output leads to accu- practice. voltage from rising above the input rately set the desired voltage with the Fig. 1 shows the circuit of the desk- voltage when a capacitive or induc- help of variable resistor VR1. You can also use your digital multimeter if the digital voltmeter is not available. Switch on S1 and set the required voltage through preset VR1 and read it on the digital voltmeter. Now the power supply is ready for use. The circuit can be wired on a common PCB. Refer Fig. 2 for pin configuration of LM317 be- fore soldering it on the PCB. Af- ter fabrication, enclose the cir- cuit in a metallic cover as shown in Fig. 3. Then open the cabinet of your PC and connect the input line of the gadget to a free (hanging) four-pin drive power connector of the SMPS Fig. 1: Circuit of desktop power supply carefully. 98 • SEPTEMBER 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM CIRCUIT IDEAS DICE WITH 7-SEGMENT DISPLAY EFY LAB CD4026, pin 14 (cascading output) is to be left unused (open), but in case of IVEDI S.C. DW A digital dice circuit can be eas- CD4033, pin 14 serves as lamp test pin ily realised using an astable and the same is to be grounded. oscillator circuit followed by The circuit uses only a handful of a counter, display driver and a dis- components. Its power consumption is play. also quite low because of use of CMOS astable oscillator configured around Here we have used a timer NE555 ICs, and hence it is well suited for bat- IC1 as well as capacitor C1 (through as an astable oscillator with a fre- tery operation. In this circuit two tac- resistor R1), which charges to the bat- quency of about 100 Hz. Decade tile switches S1 and S2 have been pro- tery voltage. Thus even after switch counter IC CD4026 or CD4033 (which- vided. While switch S2 is used for ini- S1 is released, the astable circuit ever available) can be used as counter- tial resetting of the display to ‘0,’ de- around IC1 keeps producing the clock cum-display driver. When using pression of S1 simulates throwing of until capacitor C1 discharges suffi- ciently. Thus for du- ration of depression of switch S1 and dis- charge of capacitor C1 thereafter, clock pulses are produced by IC1 and applied to clock pin 1 of counter IC2, whose count ad- vances at a frequency of 100 Hz until C1 discharges suffi- ciently to deactivate IC1. When the oscilla- tions from IC1 stop, the last (random) count in counter IC2 can be viewed on the 7-segment display. This count would normally lie between 0 and 6, since at the leading edge of every the dice by a player. 7th clock pulse, the counter is reset to Decoded Segment Outputs When battery is con- zero. This is achieved as follows. for Counts 0 through 9 nected to the circuit, the Observe the behavior of ‘b’ seg- counter and display section ment output in the Table. On reset, at around IC2 (CD4026/4033) count 0 until count 4, the segment ‘b’ is energised and the display output is high. At count 5 it changes would normally show ‘0’, as to low level and remains so during no clock input is available. count 6. However, at start of count 7, Should the display show the output goes from low to high state. any other decimal digit, you A differentiated sharp high pulse may press re-set switch S2 through C-R combination of C4-R5 is so that display shows ‘0’. To applied to reset pin 15 of IC2 to reset simulate throwing of dice, the output to ‘0’ for a fraction of a the player has to press pulse period (which is not visible on switch S1, briefly. This ex- the 7-segment display). Thus, if the tends the supply to the clock stops at seventh count, the dis- WWW.EFYMAG.COM ELECTRONICS FOR YOU • NOVEMBER 2007 • 97 CIRCUIT IDEAS play will read zero. There is a prob- other chance until the display is non- the counter by ‘1,’ the same makes the ability of one chance in seven that dis- zero. circuit somewhat complex and there- play would show ‘0.’ In such a situa- Note. Although it is quite feasible fore such a modification has not been tion, the concerned player is given an- to inhibit display of ‘0’ and advance attempted. 98 • NOVEMBER 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM circuit ideas DiGital theRmometeR s.c. dwiv edi Raj K. GoRKhali through the base-emitter junction of npn transistor BC108 (T1). The volt- T his digital thermometer can age across the base-emitter junction before the temperature is displayed measure temperatures up to of the transistor is proportional to its on the meter. Preset VR1 is used to 150°C with an accuracy of ±1°C. temperature. The transistor used this set the zero-reading on the meter and The temperature is read on a 1V full way makes a low-cost sensor. You can preset VR2 is used to set the range of scale-deflection (FSD) moving-coil use silicon diode instead of transistor. temperature measurement. voltmeter or digital voltmeter. The small variation in voltage across Operational amplifiers IC3 and IC4 Operational amplifier IC 741 (IC3) the base-emitter junction is amplified operate off regulated ±5V power sup- provides a constant flow of current by second operational amplifier (IC4), ply, which is derived from 3-terminal positive voltage regula- tor IC 7805 (IC1) and negative low-dropout regulator IC 7660 (IC2). The entire circuit works off a 9V battery. Assemble the cir- cuit on a general-pur- pose PCB and enclose in a small plastic box. Calibrate the thermom- eter using presets VR1 and VR2. After calibra- tion, keep the box in the vicinity of the object whose temperature is to be measured. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • J u ly 2 0 1 0 • 9 9 circuit ideas DiGital timeR enhancement s.c. dwiv edi Raj K. GoRKhali circuit can be used: 1. You want an appliance or gadget and relay RL1 de-energises to discon- T his simple circuit automatically to switch on automatically at a preset nect the load from mains power supply activates or deactivates an elec- time through its contacts. At this time, you tronic device at the time of alarm 2. You switch on an appliance or need to pause the alarm using pause preset in a clock. When the alarm rings, gadget manually at a particular time switch of the clock. the tone burst generated at the terminal and want it to switch off automatically When you press reset switch S1, of the buzzer triggers the circuit and the at a preset time LED1 glows to indicate that the circuit relay energises or de-energises to switch Let us see how it works when you is ready to work. When you press start on or switch off the load. want your appliance to switch on at a switch S2, LED2 glows to indicate start The circuit is built around ICs preset time, say, 3 pm. Set the alarm in mode. Glowing of LED3 means that CD40106 (IC1) and CD4017 (IC2) and your clock to 3 pm and slide switch S3 the counter has stopped counting and a few discrete components. IC1 is a hex towards Q1. When the alarm sounds needs to be reset before use. Schmitt trigger, while IC2 is a decade at 3 pm, Q0 output of IC2 advances to When the counter is in stop mode, counter. The circuit works off regulat- Q1 and relay RL1 energises to connect Q2 output of IC2 remains high. As this ed 6V power supply, while the alarm the load (appliance) to mains power pin is connected to the clock-enable clock runs off its own 1.5V battery. supply through its contacts. The load input (pin 13) of IC2, the clock input The tone burst generated at the remains ‘on’ until you reset IC2 by is inhibited. In this condition, any tone piezobuzzer is tapped from its connec- momentarily pressing S1. At this time, burst signal arriving from the clock tion points. The positive terminal of the you need to pause the alarm using has no effect on IC2 and therefore the clock buzzer is connected to the base of pause switch of the clock. circuit remains in stop mode. You can transistor T1 and the negative terminal Now suppose you manually start now set the alarm time in the clock. is connected to ground of the circuit. the load at 3 pm and want it to stop Assemble the circuit on a general- When the alarm clock sounds, the automatically at 6 pm. First, reset IC2 purpose PCB and enclose in a small signal from the clock buzzer makes by momentarily pressing S1 and slide cabinet. Connect the base of transistor transistor T1 conduct. As a result, pin switch S3 towards Q2. Set the alarm in (T1) to positive terminal of the alarm 1 of gate N1 goes low and it outputs your clock to 6 pm. To start the load, clock and negative terminal to ground high at pin 2. This low-to-high transi- press switch S2 momentarily at 3 pm. of the circuit. Put the alarm clock at a tion clocks the counter (IC2) at pin 14 The Q0 output of IC2 advances to Q1 convenient place. If you do not want to through diode D1 and gate N2. In this and relay RL1 energises to connect the use a 6V battery, replace it with a 6V way, IC2 advances by one at each clock load to mains power supply through adaptor to power the circuit. Mount produced due to the sounding alarm. its contacts. When the alarm sounds at the LEDs and the pushbutton on the There are two situations where this 6 pm, Q1 output of IC2 advances to Q2 front panel of the cabinet. 9 8 • M ay 2 0 1 0 • e l e c t ro n i c s f o r yo u w w w. e f y M ag . co M circuit ideas Drinking Water alarm s.c. dwiv edi Dr C.H. VitHalani T he State Jal Boards supply water for limited duration in a day. Time of water supply is decided by the management and the public does not know the same. In such a situation, this water alarm circuit will save the people from long wait as it will inform them as soon as the water supply starts. At the heart of this circuit is a small water sensor. For fabricating this water sensor, you need two foils—an aluminium foil and a plastic foil. You can assemble the sensor by rolling aluminium and plastic foils in the shape of a concentric cylinder. Connect one end of the insulated flexible wire on the aluminium foil and the other end to resistor R2. Now work only when water flows through from the tap. The circuit works off a 9V mount this sensor inside the water the water tap and completes the cir- battery supply. tap such that water can flow through cuit connection. It oscillates at about Assemble the circuit on any gen- it uninterrupted. To complete the 1 kHz. The output of the timer at pin eral-purpose PCB and house in a circuit, connect another wire from 3 is connected to loudspeaker LS1 via suitable cabinet. The water sensor is the junction of pins 2 and 6 of IC1 to capacitor C3. As soon as water starts inserted into the water tap. Connect the water pipeline or the water tap flowing through the tap, the speaker the lead coming out from the junc- itself. starts sounding, which indicates re- tion of 555 pins 2 and 6 to the body of The working of the circuit is sim- sumption of water supply. It remains the water tap. Use on/off switch S1 ple. Timer 555 is wired as an astable ‘on’ until you switch off the circuit to power the circuit with the 9V PP3 multivibrator. The multivibrator will with switch S1 or remove the sensor battery. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • m a r c h 2 0 0 8 • 1 0 5 circuit ideas affect operation of the IC. The two-tone DuoPhone frequencies generated are switched by edi s.c. dwiv an internal oscillator in a fast sequence, which appear at the output amplifier and drive the piezo buzzer element directly. Raj K. GoRKhali dicating a call on line 2 that is not con- The hold section is built around nected to the telephone receiver. When IC1 and IC2 . Switch S1 is used to hold T his simple circuit of a duo- you have a call on line 2, the ringer line 1 and S2 is used to put line 2 on phone allows you to access will buzz. The telephone receiver can hold. Since one telephone set is used two telephone lines through then be connected to line 2 through for two separate lines, provision is one telephone set. Each telephone con- the telephone changeover switch S4 to thus made to hold the first call while versation will remain entirely separate receive the call. the telephone set is connected to make unless you choose to combine the two The ringer section is built around or receive the second call. lines through a conference switch. Its IC3 and its associated components. Its The circuit comprises two identi- unique feature is a three-party conver- circuit uses IC 1240 to detect the ring cal hold circuits, each with its own sation/conference facility. signal and keeps the buzzer ringing flashing LED to maintain the holding The entire circuit is divided into for an incoming call on line 2. The sup- current. Each hold circuit has a timer three main sections—the ringer, hold ply voltage for the ringer is obtained LM555 (IC1 or IC2) connected as a and conferencing. The telephone set from the phone line’s AC ring (80V AC free-running oscillator operating at is connected to line 1 under normal RMS) signal and is regulated inside the a frequency of 2 Hz. The output pin conditions. The ringer is used for in- IC so that the noise on the line does not 3 of each timer is used for driving an LED that flashes twice in a second. The hold circuit is powered by the telephone lines through manually- operated hold switches (S1 and S2). Resistors R2 and R6 are placed in the hold circuits to ensure that suf- ficient current is drawn from the telephone line to prevent a discon- nection. The conferencing section is built around the audio coupling trans- former X1. Switch S3 enables three- way conversation through both the telephone lines. The transformer couples the audio signals from one telephone line to the other. At the same time, complete DC isolation is maintained between both the telephone lines. Capacitors C1 and C3 are used for preventing any DC from flowing into the transformer windings. Resistor R1 provides a holding current on line 1 when the telephone set is connected to line 2 during a conference call. Once the three-way conversation is es- tablished through the double-pole single-throw (DPST) switch S3, the hold circuits and flashing LED indi- cators are turned off. LED3, which gets illuminated by the holding cur- rent through R1, provides a visual 9 2 • N o v e m b e r 2 0 0 9 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m circuit ideas indication of the conferencing. connect switch S4 to line 1. All other nect’ plugs, you can easily remove The working of the circuit is sim- switches should be in the ‘off’ mode the unit from the telephone lines. ple. To check if the wiring of switch and all LEDs should be unlit. This Check the polarity of the telephone S4 is correct, connect the telephone permits the telephone ringer to be lines with a multimeter and connect set to line 1. Now lift up the handset activated if a call comes on line 2. For it to the circuit accordingly. and dial the number of line 2. The making calls using line 1 or line 2, To check the circuit after complet- ringer would sound. Now discon- you can simply connect switch S4 to ing the wiring, connect a 6V regulated nect line 1 and connect line 2 through the desired line. power supply to line 1. When you switch S4. You would get the dial Assemble the circuit on a gen- switch S1 to the ‘on’ position, LED1 tone from line 2. eral purpose PCB and enclose it in blinks at a rate of 2 Hz. If you flip To check a conference call, you a suitable cabinet. Fix the switches switch S1 to the ‘off’ position and would need the help of two friends. S1 through S4 on the front side of switch S3 to the ‘on’ position, LED1 First connect switch S4 to line 1 and the cabinet. Also fix the LEDs on the stops blinking and LED3 starts glow- make a call to friend 1. Now flip the front of the cabinet and the buzzer at ing, indicating that the conferencing DPST switch S3 to the ‘on’ position. the back of the cabinet. It would be facility is being used. Now disconnect This puts on hold friend 1 on line 1 better if you use telephone sockets line 1 from the 6V power supply, con- and the conference LED3 lights up. for the telephone lines. Sockets are nect it to line 2 and flip switch S2 to Connect switch S4 to line 2 and dial relatively inexpensive and save time the ‘on’ position. Now LED2 blinks at friend 2. When the call on line 2 is when troubleshooting needs to be a rate of 2 Hz. Before connecting the answered, a three-way conversation done. Use modular plugs to connect circuit to the telephone lines, flip each can be made. the circuit and the two telephone hold switch to the ‘off’ position. Now When the duophone is not in use, lines. By using such ‘quick discon- your circuit is ready to be used. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • N o v e m b e r 2 0 0 9 • 9 3 circuit ideas ElEcTRic GuiTAR PREAmPlifiER sani the o T.K. HAREENDRAN up attached to a guitar headstock is shown in Fig. 1. The pickup device has H ere is the circuit of a guitar a transducer on one end and a jack on secure optimal input impedance. With preamplifier that would ac- the other end. The jack can be plugged the component values shown here, the cept any standard guitar into a preamplifier circuit and then to input impedance is above 50 kilo-ohms a power amplifier system. and the peak output voltage is about The pickup device captures me- 2V RMS. Master-level-control potmeter chanical vibrations, usually from VR1 should be adjusted for minimal stringed instruments such as guitar distortion. pickup or violin, and converts them into an The input from guitar pickup is fed electrical signal, which can then be to this preamplifier at J1 terminal. The amplified by an audio amplifier. It signal is buffered and processed by the is most often mounted on the body op-amp circuit wired around IC TL071 jack of the instrument, but can also be at- (IC1). Set the gain using preset VR2. Headstock tached to the bridge, neck, pickguard The circuit has a master and a slave or headstock. control. RCA socket J2 is the master Fig. 1: A typical example of mounting the guitar The first part of this preamplifier signal output socket and socket J3 is pickup circuit shown in Fig. 2 is a single-tran- the slave. It is much better to take the signal from J2 as the input to the power amplifier sys- tem or sound mixer. Output signals from J3 can be used to drive a standard headphone amplifier. Using potmeter VR3, set the slave output sig- nal level at J3. House the circuit in a metallic case. VR1 and VR3 should preferably be the types with metal enclosures. To prevent hum, ground the case and the enclosures. A well- regulated 9V DC power supply Fig. 2: Guitar preamplifier circuit is crucial for this circuit. How- ever, a standard 9V alkaline pickup. It is also versatile in that it has sistor common-emitter amplifier with manganese battery can also be used to two signal outputs. degenerative feedback in the emitter power the circuit. Switch S1 is a power- A typical example of using a pick- and a boot-strapped bias divider to on/off switch. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • s e p t e m b e r 2 0 1 0 • 1 1 7 circuit ideas ELECTRIC WINDOW/FENCE CHARGER T.K. HAREENDRAN tors R2 and R3, preset VR1 and capaci- edi tor C3. The amplitude of the output s.c. dwiv H ere is the circuit of a simple pulse can be varied to some extent by electric window charger. adjusting variable resistor VR1. You With a couple of minor circuit can vary the frequency from 100 Hz variations, it can be used as an electric to 150 Hz. drives pnp transistor T1 into conduc- fence charger too. A standard 12V, 7Ah X1 is a small, iron-core, step-down tion for the duration of the time period. sealed maintenance-free (SMF) UPS transformer (230V AC primary to 12V, The collector of T1 is connected to the battery is required for powering the 1A secondary) that must be reverse base of driver transistor T2 through re- entire unit. connected, i.e., the secondary winding sistor R5. When transistor T1 conducts, Any component layout and mount- terminals of the transformer should T2 also conducts. When T2 conducts, a ing plan can be used. However, be connected between the emitter and high-current pulse flows through the try to keep the output terminals of ground and the output taken across the secondary winding of transformer X1 transformer X1 away from the circuit primary winding. Switch S1 is used for to generate a very high-voltage pulse board. Timer NE555 (IC1) is wired as power ‘on’/‘off’ and LED1 works as a at the primary winding. a free-running oscillator with narrow power-‘on’ indicator. LED2 is used to This dangerously high voltage negative pulse at the output pin 3. The indicate the pulse activity. can be used to charge the window pulse frequency is determined by resis- The output pulse from pin 3 of IC1 rails/fences. Ordinary silicon diode D1 (1N4001) protects T2 against high-voltage peaks generated by X1 inductance during the switching time. You can replace X1 with another trans- former rating, and, if necessary, replace T2 with another higher- capacity transistor. The circuit can be used to charge a 1km fence with some minor mod- ifications in the output section. Caution. Take all the relevant electri- cal safety precautions when assembling, test- ing and using this high- voltage generator. 1 1 0 • S e p t e m b e r 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m circuit ideas eLeCTrOnIC BICYCLe LOCK T.K. Hareendran J2 are two standard RCA sockets. A edi home-made security loop can be used s.c. dwiv T he electronic bicycle lock de- to link these two input points. Around scribed here is a worthwhile 50cm long, standard 14/36 flexible alternative for bicycle own- wire with one RCA plug per end is Fig. 3: Lock fitted on the bicycle tone generator UM3561 (IC1). IC1 Fig. 1: Circuit of electronic bicycle lock remains enabled until power to the circuit is turned off using switch S1 ers who want enough for the security loop. or the loop is re-plugged through J1 to make their Fig. 1 shows the circuit of the and J2. bicycles ‘intelli- electronic bicycle lock. It is powered Assemble the circuit on a general- gent’ at reason- by a compact 9V battery (6F22). purpose PCB and house in a small tin- able cost. One Key lock switch S1 and smoothing plate enclosure. Fit the system key lock of the benefits capacitor C2 are used for connect- switch (S1) on the front side of the en- of building it ing the power supply. A connected closure as shown in Fig. 2. Place RCA yourself is that loop cannot activate IC1 and there- sockets (J1 and J2) at appropriate posi- Fig. 2: Lock box the circuit can fore the speaker does not sound. tions. Now, mount the finished unit in be used for vir- When the loop is broken, zener diode place of your existing lock (as shown tually any make of bicycles. ZD1 (3.1V) receives operating power in Fig. 3) by using suitable clamps and In the circuit, input jacks J1 and supply through resistor R2 to enable screws. w w w. e f y M ag . co M e l e c t ro n i c s f o r yo u • M ay 2 0 0 9 • 8 5 circuit ideas ElEctRonic candlEs edi s.c. dwiv Raj K. GoRKhali gate trigger circuit components. It is H ere is a simple circuit that basically half-wave AC power being can produce the effect of supplied to the electric bulb. candle light in a normal The third part is the power sup- to provide better flickering effect in electric bulb. A candle light, as we ply circuit to generate regulated 5V the bulb. all know, resembles a randomly DC from 230V AC for random signal The random signal triggers the flickering light. So, the objective of generator. It comprises a stepdown gate of SCR1. The electric bulb gets this project activity is to produce a transformer (X1), full-wave rectifier AC power only for the period for randomly flickering light effect in an (diodes D3 and D4), filter capacitor which SCR1 is fired. SCR1 is fired electric bulb. (C9), followed by a regulator (IC5). only during the positive half cycles. To achieve this, the entire circuit The random signal generator of Conduction of SCR1 depends upon can be divided into three parts. The first the circuit is built around an 8-bit the gate triggering pin 3 of IC2, which part comprises IC1 (555), IC2 (74LS164), serial in/parallel out shift register is random. Thus, we see a flickering IC3 (74LS86), IC4 (74LS00) and the as- (IC2). Different outputs of the shift effect in the light output. sociated components. These generate a register IC pass through a set of logic Assemble the circuit on a general- randomly changing train of pulses. gates (N1 through N5) and final out- purpose PCB and enclose it in a suitable Fig. 1: Circuit diagram for electronic candle The second put appearing at pin 6 of gate N5 is case. Fix bulb and neon bulb on the part of the circuit fed back to the inputs of pins 1 and front side of the cabinet. Also, connect consists of SCR1 2 of IC2. The clock signal appears a power cable for giving AC mains (C106), an electric at pin 8 of IC2, which is clocked by supply to the circuit for operation. The bulb connected an astable multivibrator configured circuit is ready to use. between anode of around timer (IC1). The clock fre- Warning. Since the circuit uses Fig. 2: Pin configurations SCR1 and mains quency can be set using preset VR1 230V AC, care must be taken to avoid of C106 and 7805 live wire, and and VR2. It can be set around 100 Hz electric shock. 1 4 2 • J a n ua ry 2 0 1 0 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m ElEctronic card- lock systEm T he circuit presented here can be on and other photo-transistors will as buffer with Schmitt trigger. All outputs be used as a lock for important be in off state. When transistor T1 is (Q1 through Q7) of this IC are connected electronic/electrical appliances. on, its collector voltage falls, making to IC2 (ULN2003) which is used as relay When card is inserted inside its mecha- transistor T9 to cut-off. As a result, col- driver. IC2 consists of seven highcurrent nism, depending upon the position of lector voltage of transistor T9 as also relay drivers having integral diodes. Ex- punched hole on the card, a particu- pin 2 of IC1 go logic high. This causes ternal free-wheeling diodes are therefore lar appliance would be switched on. The card is inserted just like a floppy disk inside the disk drive. This card should be rectangular in shape with only one punched hole on it. The circuit uses eight photo-transistors (T1 through T8). When there is no card in the lock, light from incandes- cent lamp L1 (40-watt, 230V) falls on all the photo- transistor detec- tors. Transistor T8 is used as enable detector for IC1 (74LS244). When light is incident on it, it conducts and its collector voltage goes low. This makes transistor T16 to cut-off, and its collector voltage goes high. This logic high on pin 18 (output Q1) also to go high, not required. its collector terminal will inhibit IC1 switching LED1 on. Simultaneously, When an input of this IC is made logic as long as light is present on photo- output Q1 is connected to pin 1 of IC2 high, the corresponding output will go transistor T8. (ULN2003) for driving the relay cor- logic low and relay connected to that pin IC1 will get enabled only when the responding to appliance 1. Similarly, gets energised. This switches on a specific card is completely inserted inside the if card for appliance 2 is inserted, only appliance and the corresponding LED. lock mechanism. This arrangement en- output pin 16 (Q2) of IC1 will go high- Once a specific card is inserted to sures that only the selected appliance is making LED2 on while at the same switch on a specific relay, that relay switched on and prevents false operation time energising relay for appliance gets latched through its second pair of of the system. 2 via ULN2003. The same is true for contacts. Thus even when the card is You can make these cards using a other cases/appliances also. removed, the specific appliance remains black, opaque plastic sheet. A small The time during which card is pres- on. The same holds true for all other re- rectangular notch is made on this ent inside the mechanism, the system lays/appliances as well. The only way to card to indicate proper direction for generates musical tone. This is achieved deenergise a latched relay after removal insertion of the card. If an attempt with the help of diodes D1 through D7 of the corresponding card is to switch off is made to insert the card wrongly, which provide a wired-OR connection at the corresponding switch (S1 through it will not go completely inside the their common-cathode junction. When S7) which would cut-off the supply to the mechanism and the system will not any of the outputs of IC1 is logic high, desired relay. be enabled. the commoncathode junction of diodes The +5V and +12V supplies can be When card for any appliance (say D1 through D7 also goes logic high, obtained with conventional arrangement appliance 1) is completely inserted in enabling IC3 (UM66) to generate a mu- using a step-down transformer followed by the mechanism, the light will fall only sical tone. rectifier, filter and regulator (using 7805 on photo-transistor T1. So only T1 will In this circuit IC1 (74LS244) is used and 7812 etc). ELECTRONICS PROJECTS Vol. 22 13 14 ELECTRONICS PROJECTS Vol. 22 circuit ideas electronic Dice USing At89c2051 DebDoot Sheet counter variable, which, on being inter- T o his simple circuit demonstrates rupted by an external trigger, latches sani the the capability of an AT89C2051 the counter value and displays a ran- microcontrol- dom number through its output ports. ler chip to function This method is similar to the one used as a random number in PCs or calculators for generating ran- generator based on dom numbers at any instance. and uses an 18MHz crystal to generate the flying counter The application of this dice is the clock (refer Fig. 2). Switch S1 con- principle. The pro- Fig. 1: Suggested similar to the one used in a game of nected at pin 1 is used as a reset switch. gram in the chip con- LED arrangement dice. The random numbers generated Interrupt occurs at pin 6 of IC1 on logic for electronic dice stantly updates the display are not displayed numerically, but 0. Switch S2 connected to pin 6 (INT0) represented by of IC1 is used to trigger an external in- the number of terrupt to make pin 6 low. It is used as glowing LEDs. input to generate the random number. The LEDs are The random number is indicated by the dot repre- glowing of the LEDs (LED1 through sentation on the LED7) connected to port pins P1.2-P1.7 face of a dice. and P3.7. Suggested LED TL0 and TH0 act as free-wheeling arrangement for counters in auto-increment mode and the electronic constantly count up from the initial dice display is value. When the interrupt occurs, the shown in Fig. 1. value from the counter is latched and The use of glowing LEDs indicate the random IC AT89C2051 number generated by the microcontrol- (IC1) module ler chip. Assembly language is used for in the design is programming the chip. The Assembly quite simple. It code listing is self-explanatory. operates off 3- EFY note. The source code is in- Fig. 2: Circuit for electronic dice using AT89C2051 5.5V DC supply cluded in this month’s EFY-CD and w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • J u n e 2 0 1 0 • 1 0 5 CIRCUIT IDEAS ELECTRONIC HORN S.C. DW IVEDI ASHOK K. DOCTOR IC LM3900 (IC1). IC LM3900 has four independent op-amps (A1 through A4) H ere’s a simple circuit of an with a large output voltage swing. It a low-frequency squarewave genera- electronic horn that is built can work at up to 32V DC. tor. Op-amp A2 works as an integra- around quadruple op-amp The first op-amp (A1) is wired as tor, while op-amp A3 works as a comparator. A2 and A3 together When power is switched on, a ba- 9V. To generate several different work as a ‘wandering voltage gen- sic tone is generated by transistor T2 tones, connect its point A1 to pins erator’ op-amp. Op-amp A4 is wired and transformer X1, which is fre- 1, 3, 4, 5, 8, 9, 10, 11, 12 and 13 of IC1 as a buffer and its output provides quency-modulated by the wandering and point A2 to pins 1, 2, 3, 6, 8, 11 base current to npn transistor T2. npn voltage generator, which, in turn, is and 13. transistor T2 and audio output trans- influenced by the low-frequency The circuit can be used as an auto- former X1 form a voltage-controlled squarewave generator. mobile horn by using about 10W au- oscillator. The circuit works off regulated dio amplifier. WWW.EFYMAG.COM ELECTRONICS FOR YOU • JANUARY 2007 • 109 CIRCUIT IDEAS AUTOMATIC LOW-POWER SUNIL K UMAR EMERGENCY LIGHT S.C. DWIVEDI current through diode D5 and limit- ing resistor R16. By adjusting preset H ere is a white-LED-based VR1, the output voltage can be ad- emergency light that offers justed to deliver the required charg- the following advantages: ing current. 1. It is highly bright due to the use When the battery gets charged to of white LEDs. 6.8V, zener diode ZD1 conducts and 2. The light turns on automatically charging current from regulator IC1 when mains supply fails, and turns off finds a path through transistor T1 to Fig. 2: Pin configurations of LM317, BD140 when mains power resumes. ground and it stops charging of the and BC548 3. It has its own battery charger. battery. When the battery is fully charged, The LED driver section uses a to- off. On the other hand, when mains charging stops automatically. tal of twelve 10mm white LEDs. All fails, the base of transistor T2 becomes The circuit comprises two sections: the LEDs are connected in parallel low and it conducts. This makes all charger power supply and LED driver. with a 100-ohm resistor in series with the LEDs (LED1 through LED12) glow. The charger power supply section is each. The common-anode junction of The mains power supply, when available, charges the bat- tery and keeps the LEDs off as transistor T2 re- mains cut-off. During mains failure, the charging sec- tion stops working and the battery sup- ply makes the LEDs glow. Assemble the circuit on a general-pur- pose PCB and enclose in a cabinet with Fig. 1: Automatic high intensity LED-based emergency light enough space for battery and built around 3-terminal adjustable all the twelve LEDs is connected to switches. Mount the LEDs on the cabi- regulator IC LM317 (IC1), while the the collector of pnp transistor T2 and net such that they light up the room. LED driver section is built around the emitter of transistor T2 is directly A hole in the cabinet should be drilled transistor BD140 (T2). connected to the positive terminal of to connect 230V AC input for the pri- In the charger power supply sec- 6V battery. The unregulated DC volt- mary of the transformer. tion, input AC mains is stepped down age, produced at the cathode junc- EFY lab note. We have tested the by transformer X1 to deliver 9V, 500 tion of diodes D1 and D3, is fed to circuit with twelve 10mm white LEDs. mA to the bridge rectifier, which com- the base of transistor T2 through a 1- You can use more LEDs provided the prises diodes D1 through D4. Filter kilo-ohm resistor. total current consumption does not ex- capacitor C1 eliminates ripples. Un- When mains power is available, the ceed 1.5A. Driver transistor T2 can de- regulated DC voltage is fed to input base of transistor T2 remains high and liver up to 1.5A with proper heat-sink pin 3 of IC1 and provides charging T2 does not conduct. Thus LEDs are arrangement. 126 • JANUARY 2008 • ELECTRONICS FOR YOU WWW.EFYMAG.COM circuit ideas FlaSher For Deepawali s.c. dwiv edi Sunil Kumar The output of IC1 drives transistor T1. Working of the circuit is simple. H ere is the circuit for a port- When output pin 3 of IC1 goes high, able electric lamp-cum-LED transistor T1 conducts to fire TrIAC1 currents. flasher. It uses a 25W, 230V and the bulb glows. Bulb L1 turns off In brief, the bulb and the LEDs AC bulb and nine LEDs. When the when output pin 3 of IC1 goes low. flash alternately depending on the bulb glows all the LEDs remain ‘off,’ The collector of transistor T1 is con- frequency of IC1. Flashing rates of the and when the LEDs glow the bulb nected to anodes of all the LEDs (LED1 bulb as well as LEDs can be varied by remains ‘off.’ through LED9). So when T1 is cut-off adjusting potmeter Vr1. Connect the The circuit is built around timer IC the LEDs glow, and when T1 conducts power supply line (L) of mains to bulb 555 (IC1), which is wired as an astable the LEDs go off. Current-limiting resis- L1 via switch S1 and neutral (N) to multivibrator generating square wave. tor R4 protects the LEDs from higher MT1 terminal of TrIAC1. A 12V, 200mA AC adaptor is used to power the circuit. Using switch S1, you can switch off the bulb permanently if you do not want it to flash. Assemble the circuit on a general-purpose PCB and en- close in a circular plastic cabinet keeping the bulb at the centre and LEDs at the circumference. Drill holes for mounting the ‘on’/‘off’ switch. Use a bulb holder for bulb L1 and LED holders for the LEDs. Also use an IC socket for timer IC 555. Warning. While assembling, testing or repairing, take care to avoid the lethal electric shock. w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • N o v e m b e r 2 0 1 0 • 1 1 5 CIRCUIT IDEAS FLYING SAUCER IVEDI S.C. DW ASHOK K. DOCTOR T his unidentified flying object (UFO) is nothing but an elec- tronic toy depicting the fantacy. It comprises three separate sections, viz, rim flasher, dome flasher and sound generator. The rim flasher is a simple sequen- tial circuit built around timer IC 555 Fig. 1: Rim flasher (IC1) and decade counter IC CD4017 (IC2) as shown in Fig. 1. IC1 is wired as an astable multivibrator whose out- put is fed to clock pin 14 of decade counter IC2. All the eight outputs of IC2 are connected with two LEDs each. These 16 LEDs (LED1 through LED16) are arranged round the rim of a fly- ing-saucer-like toy. The colour of LEDs used may be yellow, pink orange or even white to give a good colour ef- fect. The dome flasher circuit is built around a 14-stage ripple-carry binary counter and oscillator IC CD4060 (IC3) as shown in Fig. 2. Three outputs are used here. Three groups of LEDs with six LEDs in each are arranged such that each group flashes at a different rate. Preset VR1 (47-kilo-ohm) is used to Fig. 2: Dome flasher vary the flash cycle. These 18 LEDs (LED17 through LED34) are arranged around the grove (disk) of a general-purpose PCB or veroboard, which is covered by a transparent dome. Use different- coloured LEDs for each group to cre- ate the required light effect. Red, blue, yellow or green LEDs will create a nice effect. If a transparent dome is not pos- sible, drill holes around the top to fix the LEDs. The sound generator is built around two 555 timers, two transis- tors and some discrete components as shown in Fig. 3. Timer IC5 is config- Fig. 3: Sound generator WWW.EFYMAG.COM ELECTRONICS FOR YOU • JULY 2007 • 95 CIRCUIT IDEAS ameter each. Make sure that bowls have rims to facilitate fixing of LEDs with small screws. For fixing the LEDs, refer to Fig. 4. Assemble the rim flasher, dome flasher and sound generator cir- cuits on separate gen- eral-purpose PCBs and mount these on the deep bowls along with batter- Fig. 5: Assemble unit of unidentify bird ies and speaker. PCB1, pin 5 of timer IC4. The rectangu- PCB2 and PCB3 are for rim flasher, Fig. 4: Fittings of LEDs on rim lar-wave output at pin 3 of timer dome flasher and sound generator, re- ured as an astable multivibrator. The IC5 is fed to transistor BC548 (T1) to spectively. charge-discharge cycle of capacitor C8 operate timer IC4, which is also an The assembled flying (47µF) generates a sawtooth waveform asymmetrical multivibrator. If a 75- saucer is shown in Fig. 5. When you which rises rapidly but falls slowly. ohm-impedance speaker is available, switch on the circuit, rim LEDs and This waveform is fed to the base of there is no need to use resistor R16 (68 dome LEDs flash, and at the same transistor T2 (BC327), which is an emit- ohms). time, a sound is generated. This gives ter follower. Its output is used to con- For assembling the circuit, use two the simulated effect of an unidentified trol frequency modulation. It is fed to deep, plastic bowls of about 20 cm di- flying object. 96 • JULY 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM circuit ideas Four-StaGe FM tranSMitter s.c. dwiv edi PradeeP G. the pre-driver stage. You can also use transistor 2N5109 in place of 2N2219. T his FM transmitter circuit uses The preamplifier is a tuned class-A RF frequency generated. You can also use four radio frequency stages: amplifier and the driver is a class-C a 12V battery to power the circuit. a VHF oscillator built around amplifier. Signals are finally fed to the Assemble the circuit on a general- transistor BF494 (T1), a preamplifier class-C RF power amplifier, which de- purpose PCB. Install the antenna prop- built around transistor BF200 (T2), a livers RF power to a 50-ohm horizontal erly for maximum range. driver built around transistor 2N2219 dipole or ground plane antenna. Coils L1 through L5 are made with (T3) and a power amplifier built Use a heat-sink with transistor 20 SWG copper-enamelled wire wound around transistor 2N3866 (T4). A con- 2N3866 for heat dissipation. Carefully over air-cores having 8mm diameter. denser microphone is connected at the adjust trimmer VC1 connected across They have 4, 6, 6, 5 and 7 turns of wire, input of the oscillator. L1 to generate frequency within 88- respectively. Working of the circuit is simple. 108 MHz. Also adjust trimmers VC2 EFY note. This transmitter is meant When you speak near the microphone, through VC7 to get maximum output only for educational purposes. use of frequency-modulated signals are at maximum range. this transmitter with outdoor antenna obtained at the collector of oscillator Regulator IC 78C09 provides stable is illegal in most parts of the world. The transistor T1. The FM signals are am- 9V supply to the oscillator, so variation author and EFY will not be responsible plified by the VHF preamplifier and in the supply voltage will not affect the for any misuse of this transmitter. w w w. e f y M ag . co M e l e c t ro n i c s f o r yo u • M a r c h 2 0 1 0 • 1 0 3 CIRCUIT IDEAS FULLY AUTOMATIC EMERGENCY LIGHT DR C.H. VITHALANI built around 3-terminal adjustable regulator LM317. IVEDI S.C. DW T his simple automatic emer- In the inverter section, NE555 is gency light has the following wired as an astable multivibrator that advantages over conventional produces a 15kHz squarewave. Out- emergency lights: put pin 3 of IC 555 is connected to the 1. The charging circuit stops auto- Darlington pair formed by transistors minals of each side of the tubelight matically when the battery is fully SL100 (T1) and 2N3055 (T2) via resis- and then connect to the secondary of charged. So you can leave the emer- tor R4. The Darlington pair drives fer- X1. (You can also use a Darlington pair gency light connected to AC mains rite transformer X1 to light up the of transistors BC547 and 2N6292 for a overnight without any fear. tubelight. 6W tubelight with the same trans- 2. Emergency light automatically For fabricating inverter transformer former.) turns on when mains fails. So you X1, use two EE ferrite cores (of When mains power is available, re- don’t need a torch to locate it. 25×13×8mm size each) along with plas- set pin 4 of IC 555 is grounded via 3. When mains power is available, tic former. Wind 10 turns of 22 SWG transistor T4. Thus, IC1 (NE555) does emergency light automatically turns on primary and 500 turns of 34 SWG not produce squarewave and emer- off. wire on secondary using some insula- gency light turns off in the presence The circuit can be divided into in- tion between the primary and second- of mains supply. verter and charger sections. The in- ary. When mains fails, transistor T4 verter section is built around timer To connect the tubelight to ferrite does not conduct and reset pin 4 gets NE555, while the charger section is transformer X1, first short both ter- positive supply though resistor R3. IC1 (NE555) starts producing square wave and tubelight turns on via ferrite transformer X1. In the charger section, input AC mains is stepped down by transformer X2 to deliver 9V-0- 9V AC at 500 mA. Diodes D1 and D2 rectify the output of the transformer. Capacitors C3 and C4 act as filters to eliminate ripples. The unregulated DC voltage is fed to IC LM317 (IC2). By adjusting preset VR1, the output voltage can be adjusted to deliver the charging voltage. When the battery gets charged above 6.8V, zener diode ZD1 conducts and regulator IC2 stops delivering the charging voltage. Assemble the circuit on a general-purpose PCB and en- close in a cabinet with enough space for the battery and switches. Connect a 230V AC power plug to feed charging voltage to the battery and make a 20W tube outlet in the cabinet to switch on the tubelight. 100 • FEBRUARY 2007 • ELECTRONICS FOR YOU WWW.EFYMAG.COM circuit ideas Generator rooM liGht s.c. dwiv edi Manuj Paul erator room light, while Fig. 2 shows the battery charger circuit, which is IC1 remain high, making output pin 3 A t night when power fails, one optional and can be omitted if the gen- of IC1 low and transistor T2 cut-off. So finds it difficult to reach the erator is self-start type and has built-in lamp L1 connected between the collec- generator to start it. Here is battery. tor of T1 and the positive terminal of the circuit for a generator room light At the heart of the generator room 12V supply does not glow. that automatically turns on at night, light circuit (Fig.1) is a light-dependent As the ambient light fades dur- facilitating easy access to the generator. resistor (LDR1) that senses the ambi- ing sunset, the resistance of LDR1 During daytime, the light remains off. ent light as well as light from glowing increases. As a result, the voltage drop Fig. 1 shows the circuit for gen- LED1. across LDR1 increases and npn transis- tor T1 conducts. Pins 2 and 6 of IC1 go low to make its output pin 3 high, and lamp L1 glows. You can replace incan- descent lamp L1 with bright white LEDs using proper current-limiting resistors. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Install the unit near the gen- erator. Arrange LED1 and LDR1 such that during the availability of mains, light emitted from LED1 falls di- rectly on LDR1. Also, make sure that during daytime the ambient light falls on the LDR. For powering the battery Fig. 1: Circuit for generator room light charger circuit (Fig. 2), 15V AC secondary voltage is During derived from step-down transformer daytime, sun- X1. For fast charging of the battery, light or light you may increase the current rating of from LED1 transformer X1. reduces the The charger charges the battery resistance through a thyristor (SCR1) when the of LDR1. As battery voltage is low. The thyristor a result, the gets a regulated gate voltage from the voltage drop zener diode, and goes to tickle charg- across LDR1 ing mode when the battery voltage decreases and nears the zener voltage. npn transistor Assemble the charger circuit on a T1 does not general-purpose PCB and enclose in conduct. The a suitable cabinet. Use two crocodile collector of T1 clips (red for positive and black for and therefore negative) for connecting the battery Fig. 2: Battery charger circuit (optional) pins 2 and 6 of terminal to the charger circuit. 8 4 • J u ly 2 0 0 9 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m
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