DEVELOPMENT OF SOLAR POWER BASED ASAS

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					                                                    DEVELOPMENT OF SOLAR POWER BASED ASAS



                                1. INTRODUCTION
           A variety of factors including the increasingly ageing population require more
care services to be delivered to users in their own homes. As a result, the development of
home care systems has been a crucial research field for both academics and engineers.
However, most research work was focused on home-care health services for patients such as
hi-tec home-care environment, smart-phone-based support system, wireless application
protocol, mobile telemedicine system, etc .

              For elder or disabled people who are still in a good health condition, a friendly
living environment, e.g., moderate indoor sunlight, is in- deed an indispensable issue.
Therefore, one of the solutions can be achieved by an automatic shutter control system. This
study proposes a local-loop shutter action control module with open architecture based on the
well-known microprocessors , i.e. Intel 8051 . Every shutter action can be carried out
according to the condition of pre-defined sunlight strength. A suitable shutter action using the
solar power can be thus achieved accurately and rapidly.

             This paper is organised based on the automatic sunlight adjusting system for
homecare. It introduces a profile of the proposed system architecture, focusing on the
hardware system and the software system using the microprocessor (8051) is provided. The
proposed system can keep sunlight moderate as desired in the indoor room. Once the solar
battery power is insufficient to support the system, the system power can be switched to AC
source immediately using the AC/DC switching system (ASS). This mechanism in deed
extends the green power applications and is very feasible for general facilities that require no
large power. Real practical performance results are presented to demonstrate the effectiveness
of the proposed approach in term of simple, flexible and efficient performance.




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                              2. SHUTTER PROFILE




                                        Fig.1 Shutter Profile

       This is the shutter profile used instead of windows and a spiral shaft is used here. Two
12V DC motors are placed to control the shutter up-down action and shutter blade rotating
action respectively. This system works based on the pre-defined sunlight strength given as
microcontroller program. Initially the sensor signal converter is to convert the sensor signal
into two digital signals that are read by the microprocessor.
         After signal processing, the microprocessor can provide appropriate motor control
signals and select a PWM (pulse width-modulation) signal for the DC motor speed operation.
The shutter position controlled by the DC motor is thus adjusted to reach the moderate
condition. The shutter full open and full close situation can be detected by the position-
limited circuit. When the output signals from the light sensor signal converter, are received
by the microprocessor, the motor driver will be activated. The system also provides a 4-speed
PWM signal selection as well as the motor control signals. The motor can perform the
function like start, speedup, slow-down, brake or stop under a desired speed. Consequently,
the sunlight amount controlled by the shutter height can be always kept at a desired
comfortable level.




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3. ARCHITECTURE OF SOLAR POWER BASED ASAS




                           Fig.2 Architecture of ASAS
        When the output signals from the sensor signal converter are received by the
microprocessor, the motor driver will be activated properly soon after the signal processing.
The system also provides a 4-speed PWM signal selection as well as the motor control
signals. The motor can perform the function like start, speed-up, slow-down, brake or stop
under a desired speed. Consequently, the sunlight amount controlled by the shutter height can
be always kept at a desired comfortable level.


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                                      4. WORKING

 Its architecture consists of two crucial parts:
                           1. AC/DC Switching System
                           2. Shutter Control System
The AC/DC Switching System includes
       solar power battery
       AC power
       AC/DC converter
       AC/DC Power Switching (APS) Circuit.

4.1 AC/DC Power Switching Circuit

       The AC/DC Power Switching (APS) Circuit plays the key role in the AC/DC
Switching System and mainly consists of three parts:
                               Sub-switching Circuit
                               Voltage Level Checking (VLC) circuit
                               Main-switching Circuit.
       The DC power supply (Vcc = 10V) for VLC circuit is from either the solar power
battery or AC/DC converter, depending on the status of N.C. and N.O. switches of the Sub-
switching Circuit. The action of N.C. and N.O. switches in the Sub switching Circuit is
simultaneously operated by the relay in the Main-switching Circuit.




                               Fig.3 AC/DC Power Switching Circuit

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 Vref = Vin× [ 100k÷(27k+100k) ]

      = 0.79Vin                                                                           (4.1.1)

Set the upper limit Vu as the inverting input of the Upper limit Comparator as follows.

Vu = Vcc × [ 100k÷(1.3k+100k)]

   =10× 0.987

   = 9.9V                                                                                 (4.1.2)

Set the lower limit Vd as the non-inverting input of the Lower-limit Comparator as follows.

VL = V × [ 100k÷(6.6k+100k)]

  = 10 × 0.938

  = 9.4V                                                                           (4.1.3)
Both the outputs of the Upper-limit and Lower-limit comparators are connected with the
inputs of SR Flip Flop. Therefore, the battery power starts to be used when the battery
voltage is beyond 12.53 V, and it works continuously until its voltage is down to 11.89 V.
This battery power is given to the shutter control system.

4.2 SHUTTER CONTROL SYSTEM
      This constitutes:

   1. A group of Cadmium Sulphide Light Sensors
   2. Light Sensor Signal Converter
   3. Shutter Up-Down Control System
   4. Shutter Blade Control System

     Each System consists of

                      8051 microcontroller
                      4-speed PWM Circuit
                      Motor Driver
                      DC Motor
                      Position limited Circuit




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                      Initially, the 5-selective switch provides an optional resistor to choose
                      an applicable light sensing range. The light sensor signal converter
                                                                                  converts the
                                                                                  sensor signal
                                                                                  into two
                                                                                  digital




                        Fig. 4 Shutter Control System Architecture


signals (VL and VH) that are read by the microprocessors (8051 (A) and 8051 (B)). The 8051
(A) is to control the shutter up-down action, and 8051 (B) is to control the shutter blade


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rotating action. Each microprocessor can provide its appropriate motor control signals and
select a PWM (pulse width-modulation) signal for the DC motor speed operation. The shutter
full open and full close situation can be detected by the position-limited circuit.
        The port 3 of the microprocessor is employed to send out the control signals to the
shutter control circuit, shown in Fig.2. Table 1 indicates the defined function between the
port 3 and motor operation. The lowest two bits , i.e., port bits 3.0 to 3.1 , are to control the
motor action. The bits (u, v) can be (0,1) and (1,0) for motor forward and reverse control,
respectively. Another four bits , i.e., port bits 3.2 to 3.5, are used for the motor speed
selection. On the other hand, the position signal from the position-limited circuit can be read
by p 1.4 and p 1.5.
                Table 1. Function definition of the port 3 and motor operation
        P3.7 P3.6       P3.5    P3.4    P3.3    P3.2   P3.1    P3.0    Motor
                                                                       Function
        x       x       X       X       X       X      0       0       Motor brake
        x       x       X       X       X       X      1       1       Motor stop
        x       x       0       0       0       1      u       v       ¼ motor speed
        x       x       0       0       1       0      u       v       2/4 motor speed
        x       x       0       1       0       0      u       v       ¾ motor speed
        x       x       1       0       0       0      u       v       Full motor
                                                                       speed


        When the output signals from the light sensor signal converter, shown are received by
the microprocessor, the motor driver will be activated. The system also provides a 4-speed
PWM signal selection as well as the motor control signals. The motor can perform the
function like start, speedup, slow-down, brake or stop under a desired speed.

        Consequently, the sunlight amount controlled by the shutter height can be always
kept at a desired comfortable level. The sensor signal converter consists of two detector
circuits, i.e., strong sunlight detector and weak sunlight detector. The sunlight sensitivity can
be adjusted by the 5-selective resistors (10k, 12.5k, 15k, 17.5k, 20 k). In the strong sunlight
detector, the transistor Q1 will be operated beyond the uppermost limitation of strong
sunlight situation, i.e., Vcds ~ 4.IIV , referring to the equation .




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                              Fig.5 Sensor Signal Converter

        Under this circumstance, Q1 is turned on so that Q2,Q3 and Q4 are soon conducted,
and the path of 1 k is thus short-circuited. Consequently, the motor will then drive the shutter
down until a moderate sunlight condition is reached, i.e., Vcds < 3.9V , referring to the
equation . During the shutter-down period, VH is kept at a high level (5V) , but VH remains
at a low level (0V) in the other situations. Consider that the sunlight is at a weak situation,
i.e.,Vcds < 3.8V . The output signal (VL) of the weak sunlight detector will be pulled up at a
high level (5V). Therefore, the shutter is driven up to attract more sunlight until Vcds ~ 3.9V
, referring to the equation . Once Vcds ~ 3.9V, the VL will be soon changed into the high
level (5V), referring to the equation. The shutter-up action then stops unless , < 3.8V again.
Accordingly, the moderate sunlight, i.e., 3.8V < Vcds < 4.IIV, can be maintained in this case.


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As above, it indicates that both detectors can balance the sunlight strength between 3.8V and
4.11 V. The definition of sunlight strength is presented in Table 2.

                      Table 2. Definition of sunlight strength

                 Sensor Signal                                Sunlight Strength
   Vcds ≥ 4.11V                                      Strong
   3.8 V< Vcds < 4.11 V                              Moderate
   Vcds ≤ 3.8V                                       Weak


Q1 is activated when its base voltage is beyond the following voltage (VQ1H), and Q1 will be
kept operated until the base voltage is down below VQ1L.

VQ1H =

     = 4.11V                                                                            (4.2.1)

VQ1L =

     = 3.9 V                                                                            (4.2.2)
Similarly, Q5 is activated when its base voltage reaches the following voltage (VQ5H ), and
Q5 will remains to be operated until the base voltage falls down below VQ5L.

VQ5H =

     = 3.9V                                                                       (4.2.3)

VQ5L =


     = 3.8V                                                                            (4.2.4)

For safety consideration and position fixing purpose, the boundary of shutter action
movement is restricted using the position-limited circuit. The limit switches (LS0 and LS




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are to detect the shutter uppermost and lowest status.




            Fig.6 Position Limit Switch




               Fig. 7 Profile of sensor signals over motor operation status




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  5. SOFTWARE OF THE SHUTTER PERFOMANCE




                        Fig. 8 Flowchart of shutter control program




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Soon after the output (digital) signals (VL,VH) converted via the sensor signal converter are
read by the microprocessor, the shutter control system is then activated using the shutter
control program, shown . Note that (A) and (B) are the connection labels. The shutter control
procedure is described briefly as follows.
(a) Check the strength of sunlight.
(b) If the sunlight is moderate, i.e., (VL, VH ) = (1,0) , the shutter stops and go to step (e).
Wait for a time delay and go back the step (a). Otherwise, continue next step.
(c) Check if the sunlight is strong, i.e., (VL, VH) = (I1,1). If yes, pull the shutter down for a
short period time and stop the shutter. If no, the sunlight is located at a weak
situation. Therefore, pull the shutter up for a short period time and stop the shutter.
(d) Go to the blade rotating program.
(e) Check the system is required to stop. If yes, stop the system. Otherwise, go back to step
(a) after time delay .
          The blade rotating program included in the shutter control program is to adjust the
blade degree to alter the amount of indoor sunlight , and it is described briefly
as follows.
(a) Rotate the blade degree toward a close direction for a short period time. Check if the
sunlight is moderate. If yes, stop the blade rotating and go to step (e). Otherwise ,go to next
step.
(b) Check if the blade touches the down-limit. If yes, stop the blade rotating and go next
step. Otherwise, go back step (a).
(c) Rotate the blade degree toward an open direction for a short period time. Check if the
sunlight is moderate. If yes, stop the blade rotating and go to step (e). Otherwise, go to
(d) Check if the blade touches the up-limit. If yes, stop the blade rotating and go next step.
Otherwise, go back step (a).
(e) Go to Label B.
(f) Delay 0.01 sec.
(g) Check if the LS0 is touched (p1.0=0). If yes, go to step
(s). Otherwise, reverse the motor using full speed and go
to next step.
(h) Delay 0.01 sec.
(i) Check if the LS0 is touched (p1.0=0). Otherwise, decrease D=D-1 and go to next step.
(j) Check if the D=0. If yes, reducing the motor speed using 3/4 speed and go to next step.
Otherwise, go back to step(g).

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(k) Delay 0.01 sec.
(l) Reducing the motor speed to 2/4 speed and go to nextstep.
(m) Delay 0.01 sec.
(n) Check if the LS0 is touched (p1.0=0). If yes, go to step




                          Fig.9 Flowchart of blade rotating program




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                               6. PWM GENERATION

 6.1 Pulse Width Modulation

            Pulse Width Modulation (PWM) is a common technique for speed control which
can overcome the problem of the poor starting performance of a motor.

A good analogy is bicycle riding. You peddle (exert energy) and then coast (relax) using
your momentum to carry you forward. As you slow down (due to wind resistance, friction,
road shape) you peddle to speed up and then coast again. The 'duty cycle' is the ratio of
peddling time to the total time (peddle + coast time). A 100% duty cycle means you are
peddling all the time, and a 50% duty cycle means you are peddling only half the time.

PWM for motor speed control works in a very similar way. Instead of supplying a varying
voltage to a motor, it is supplied with a fixed voltage value (such as 12V) which starts it
spinning immediately. The voltage is then removed and the motor 'coasts'. By continuing
this voltage on/off cycle with a varying duty cycle, the motor speed can be controlled.

The waveforms in figure 1 help to explain the way in which this method of control
operates. In each case the signal has maximum and minimum voltages of 12V and 0V.

      In waveform 1a, the signal has a mark-space ratio of 1:1. With the signal at 12V for
       50% of the time, the average voltage is 6V, so the motor runs at half its maximum
       speed.
      In waveform 1b, the signal has a mark-space ratio of 3:1, which means that the output
       is at 12V for 75% of the time. This clearly gives an average output voltage of 9V, so
       the motor runs at 3/4 of its maximum speed.
      In waveform 1c, the signal has a mark-space ratio is 1:3, giving an output signal that
       is 12V for just 25% of the time. The average output voltage of this signal is just 3V,
       so the motor runs at 1/4 of its maximum speed.

By varying the mark-space ratio of the signal over the full range, it is possible to obtain any
desired average output voltage from 0V to 12V. The motor will work perfectly well,
provided that the frequency of the pulsed signal is set correctly, a suitable frequency being
30Hz. Setting the frequency too low gives jerky operation, and setting it too high might
increase the motor's impedance.

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                      Fig.10 PWM Waveforms


6.2 PWM motor control

        The control of electric motors is something which interests nearly everyone
involved with Meccano model building. Every model has its own motor requirements with
regard to the space available, the power of the motor, its speed, whether it must stop and
start frequently, and the need for reduction gearing.

On the face of it, simple methods of control are perfectly adequate, with a regulated voltage
supply, a simple on/off switch, and the means to reverse the motor. Speed can be controlled
with a wire-wound potentiometer (variable resistor) or a circuit such as the Darlington Pair
Speed Control.

In reality, these methods can provide very unrealistic results. The main problem is poor
starting performance, the motor tending to jump almost instantly from a stationary position
to what is often more than half speed. The main cause of this seems to be the starting
characteristic of the motor itself which when under load seems reluctant to start.

          A motor has a relatively low resistance when it is stationary. As the speed control
is advanced, the current through the motor increases, but the voltage across the motor
remains quite low. The speed control therefore has to be well advanced before the voltage
and power fed to the motor are high enough to overcome its reluctance to start. As the



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motor speed and the load on it changes, there are changes in its internal resistance. Speed
regulation is not very good under these circumstances, particularly at low speed.


6.3 PWM Generation Circuit

          The concept of PWM inherently requires timing. Two 555 timer ICs and some
potentiometers can be used to generate a PWM signal, and since PWM provides a digital,
on/off signal, it is also easy to use a PC or micro-controller to create the signal; however
this is beyond the scope of this article.

The circuit in figure 2 uses two 555 ICs and is actually a combination of two types of
circuit. The first is a free running multivibrator (astable) with an adjustable frequency
around 30Hz. The output of this circuit then triggers a pulse shaping (monostable) circuit
which adjusts the width of the pulse. The circuit produces a duty cycle in the range of
approximately 0.3% to 97%.

The speed of the motor is controlled with a single potentiometer (variable resistor). It is
possible to run a Meccano M5 motor to test the circuit, and it will run from dead still to full
speed using the potentiometer speed control and a 6V battery as the sole power source. If
you have a 12V motor, you can of course use a 12V power source.

The motor is switched on and off via a TIP31C transistor (shown in figure 3) which can
handle motors rated up to 3A at 100V, or a total power of 40W. If you are using a high
power motor, make sure there is a heat sink bolted to the transistor.

The nature of this circuit means that the motor can never be fully switched off. However,
the minimum 0.3% duty cycle should be low enough to effectively stop the motor running.

When you first switch the circuit on and move the speed potentiometer slowly from its
minimum position to its maximum position, you will probably find that the speed of the
motor increases linearly, then suddenly drops slightly before increasing again. This is due
to the pulse width becoming longer than the time allowed for it by the 555 astable.

The frequency preset of the 555 astable circuit solves this problem by allowing the
frequency of the signal to be adjusted so that the speed potentiometer can achieve its full
range. To calibrate it, set the speed potentiometer to its maximum position, then adjust the

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frequency preset so that the motor runs as fast as possible. If you have a multimeter that
can measure frequency, you can check the modulation frequency at pin 3 of the 555 astable,
and confirm the range of the duty cycle at pin 3 of the monostable.




                        Fig.11 LM 3524


Features


                                                -down




                                             -amp
                           se suppression)




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Description

        The LM3524D family is an improved version of the industry standard LM3524. It
has improved specifications and additional features yet is pin for pin compatible with existing
3524 families. New features reduce the need for additional external circuitry often required in
the original version.

The LM3524D has a ±1% precision 5V reference. The current carrying capability of the
output drive transistors has been raised to 200 mA while reducing VCEsat and increasing VCE
breakdown to 60V. The common mode voltage range of the error-amp has been raised to
5.5V to eliminate the need for a resistive divider from the 5V reference.

In the LM3524D the circuit bias line has been isolated from the shut-down pin. This prevents
the oscillator pulse amplitude and frequency from being disturbed by shut-down. Also at high
frequencies (≃300 kHz) the max. duty cycle per output has been improved to 44% compared
to 35% max. duty cycle in other 3524s.

In addition, the LM3524D can now be synchronized externally, through pin 3. Also a latch
has been added to insure one pulse per period even in noisy environments. The LM3524D
includes double pulse suppression logic that insures when a shut-down condition is removed
the state of the T-flip-flop will change only after the first clock pulse has arrived. This feature
prevents the same output from being pulsed twice in a row, thus reducing the possibility




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                                  7. COMPONENTS USED

                 Table 3. components of working model.

     ITEM NO.     INSTRUMENT NAME            SPECIFICATIONS
     1           Microprocessor              Intel8051
     2           Motor Driver                SI-5300: Full Bridge PWM
                                             Control DC Motor Drive
     3           PWM Generation Circuit LM3524:Regulating Pulse
                                             Width Modulator
     4           One-shot Circuit            LM 555: Single Timer
     5           DC Motor                    12V 71 RPM
     6           Limit switch                15 A 1/2 HP
     7           Digital IC                  IC 7408 ,    IC 7432
     8           Transistors                 9013 (npn) and 9012(pnp)
     9           Light Sensor                Cds
     10          Solar Battery               12V
     11          Buffer                      IC 741




7.1 FULL-BRIDGE PWM MOTOR DRIVER

          SI-5300 incorporates two high side Pch MOSFETs two low side Nch MOSFETs
and a control IC in one package. Overcurrent protection function for each power Switch and
thermal shutdown function for control IC. Also, the dead time (20μS) is set in the control IC
to prevent turning on the high side MOSFETs at the same time




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                 Fig. 12 Typical connection of PWM motor driver (SI- 5300)
      Two Pch MOSFETs for high side power switches two Nch for low side and one
control IC are integrated into one package.
Enables to drive a motor by DC drive at upto 5A DC or by pulse drive at upto 16A .
       PWM input is 20khz maximum and phase changeover frequency is 500 hz maximum
. Input signals for input one and input two control the output of each phase with normal
reverse, brake and free run mode. In order to prevent shoot through current during phase
changeover ,the control IC set the dead time. Dead time 20µs typically.
      Versatile protection functions are over current protection for each power switch ,
thermal shutdown(TSD), DIAG output function: outputs the diagnosis during abnormal
operation . Applications are driving various dc motors , throttle valve for automotive
application. Features encorporates two high side Pch MOSFET two low side Nch
MOSFETs,and a control IC in one package. Overcurrent protection function for each power
switch the thermal shutdown function for control IC . Also the dead time 20 us is set in the
control IC to prevent timing on the high side MOSFETS at the same timing.
7.2 CADMIUM SULPHIDE LIGHT SENSOR

                 The Mind storms Light sensor is based on a silicon photo transistor that is
mostly sensitive to Infrared light. It has trouble with low light levels since the built-in LED
light source leaks into the detector. Radio Shack sells a package of 5 Cadmium Sulfide (CdS)
photoresistors, catalog number 276-1657, for only $2.29 that provide a more visible range of

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spectral sensitivity and also a wider range of photo sensitivity than the LEGO Light Sensor.
The picture below shows prototype constructed with the Dean Husby cut up LEGO Electric
Plate method. The sensor is used by setting the sensor type to 0 and reading the Raw values
from 0 to 1023. It may seem confusing, but the brighter the light the lower the Raw value.




                    Fig. 13 Cadmium sulphide light sensor

      The plot below shows how the CdS photoresistor is the most sensitive to visible light. The
       only disadvantage to CdS photoresistors is that they are relatively slow to respond to changes
       of light levels. They can take several seconds to change to a new value. Here is a plot that
       tells you what RCX Raw values to expect to see given the light level. The measurements with
       the CdS photoresistor held next to a photographic light meter and plotted the light meter
       readings to units of light intensity or Foot Lamberts and common descriptions of the light
       conditions. Also shown is a plot relating the LEGO Light sensor reading to the CdS Raw
       reading.
      The cadmium sulfide (CdS) or light dependent resistor (LDR) whose resistance is
       inversly dependent on the amount of light falling on it, is known by many names
       including the photo resistor, photoresistor, photoconductor, photoconductive cell, or
       simply the photocell.
      A typical structure for a photoresistor uses an active semiconductor layer that is
       deposited on an insulating substrate. The semiconductor is normally lightly doped to
       enable it to have the required level of conductivity. Contacts are then placed either
       side of the exposed area.




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                                   Fig.14 Cds spectral response
       The photo-resistor, CdS, or LDR finds many uses as a low cost photo sensitive element
and was used for many years in photographic light meters as well as in other applications
such as smoke, flame and burglar detectors, card readers and lighting controls for street
lamps.
       Providing design engineers with an economical CdS or LDR with high quality
performance, Token Electronics now offers commercial grade PGM photoresistor.
Designated the PGM Series, the photoresistors are available in 5mm, 12mm and 20mm sizes,
the conformally epoxy or hermetical package offer high quality performance for applications
that require quick response and good characteristic of spectrum.
Token has been designing and manufacturing high performance light dependent resistors for
decades. Our product offerings are extensive and our experience with custom photoresistor is
equally extensive. Contact us with your specific needs.
Features :
        Quick Response
        Reliable Performance
        Epoxy or hermetical package
        Good Characteristic of Spectrum




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Applications :
      Photoswitch
      Photoelectric Control
      Auto Flash for Camera
      Electronic Toys, Industrial Control
7.3 8051 MICROCONTROLLER
         Despite it’s relatively old age, the 8051 is one of the most popular microcontrollers
in use today. Many derivative microcontrollers have since been developed that are based
on—and compatible with--the 8051. Thus, the ability to program an 8051 is an important
skill for anyone who plans to develop products that will take advantage of microcontrollers.
The 8051 has three very general types of memory. To effectively program the 8051 it is
necessary to have a basic understanding of these memory types. On-Chip Memory refers to
any memory (Code, RAM, or other) that physically exists on the microcontroller itself. On-
chip memory can be of several types, but we'll get into that shortly.
          External Code Memory is code (or program) memory that resides off-chip. This is
often in the form of an external EPROM. External RAM is RAM memory that resides off-
chip. This is often in the form of standard static RAM or flash RAM. Code Memory Code
memory is the memory that holds the actual 8051 program that is to be run. This memory is
limited to 64K and comes in many shapes and sizes: Code memory may be found on-chip,
either burned into the microcontroller as ROM or EPROM. Code may also be stored
completely off-chip in an external ROM or, more commonly, an external EPROM.
Flash RAM is also another popular method of storing a program. Various combinations of
these memory types may also be used that is to say, it is possible to have 4K of code memory
on-chip and 64k of code memory off-chip in an EPROM. When the program is stored on-chip
the 64K maximum is often reduced to 4k, 8k, or 16k. This varies depending on the version of
the chip that is being used.
        Each version offers specific capabilities and one of the distinguishing factors from
chip to chip is how much ROM/EPROM space the chip has. However, code memory is most
commonly implemented as off-chip EPROM. This is                  especially true in low-cost
development systems and in systems developed by students. Programming Tip: Since code
memory is restricted to 64K, 8051 programs are limited to 64K. Some assemblers and
compilers offer ways to get around this limit when used with specially wired hardware.
However, without such special compilers and hardware, programs are limited for 64K .


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                                Fig.15 Block diagram of 8051
         External RAM As an obvious opposite of Internal RAM, the 8051 also supports what
is called External RAM. As the name suggests, External RAM is any random access memory
which is found off-chip. Since the memory is off-chip it is not as flexible in terms of
accessing, and is also slower. For example, to increment an Internal RAM location by 1
requires only 1 instruction and 1 instruction cycle.
         To increment a 1-byte value stored in External RAM requires 4 instructions and 7
instruction cycles. In this case, external memory is 7 times slower. What External RAM loses
in speed and flexibility it gains in quantity. While Internal RAM is limited to 128 bytes the
8051 supports External RAM up to 64K. Programming Tip: The 8051 may only address 64k
of RAM. To expand RAM beyond this limit requires programming and hardware tricks. You
may have to do this "by hand" since many compilers and assemblers, while providing support
for programs in excess of 64k, do not support more than 64k of RAM.
         This is rather strange since it has been my experience that programs can usually fit in
64k but often RAM is what is lacking. Thus if you need more than 64k of RAM, check to see
if your compiler supports it-- but if it doesn't, be prepared to do it by hand
7.4 DC MOTOR

         A DC motor is designed to run on DC electric power. Two examples of pure DC
designs are Michael Faraday's homopolar motor (which is uncommon), and the ball bearing
motor, which is (so far) a novelty. By far the most common DC motor types are the brushed
and brushless types, which use internal and external commutation respectively to create an
oscillating AC current from the DC source so they are not purely DC machines in a strict
sense.




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Brushed DC motors

        DC motor design generates an oscillating current in a wound rotor, or armature, with
a split ring commutator, and either a wound or permanent magnet stator. A rotor consists of
one or more coils of wire wound around a core on a shaft; an electrical power source is
connected to the rotor coil through the commutator and its brushes, causing current to flow in
it, producing electromagnetism. The commutator causes the current in the coils to be
switched as the rotor turns, keeping the magnetic poles of the rotor from ever fully aligning
with the magnetic poles of the stator field, so that the rotor never stops (like a compass needle
does) but rather keeps rotating indefinitely (as long as power is applied and is sufficient for
the motor to overcome the shaft torque load and internal losses due to friction, etc.)

        Many of the limitations of the classic commutator DC motor are due to the need for
brushes to press against the commutator. This creates friction. Sparks are created by the
brushes making and breaking circuits through the rotor coils as the brushes cross the
insulating gaps between commutator sections. Depending on the commutator design, this
may include the brushes shorting together adjacent sections—and hence coil ends—
momentarily while crossing the gaps. Furthermore, the inductance of the rotor coils causes
the voltage across each to rise when its circuit is opened, increasing the sparking of the
brushes. This sparking limits the maximum speed of the machine, as too-rapid sparking will
overheat, erode, or even melt the commutator. The current density per unit area of the
brushes, in combination with their resistivity, limits the output of the motor. The making and
breaking of electric contact also causes electrical noise, and the sparks additionally cause
RFI. Brushes eventually wear out and require replacement, and the commutator itself is
subject to wear and maintenance (on larger motors) or replacement (on small motors). The
commutator assembly on a large motor is a costly element, requiring precision assembly of
many parts. On small motors, the commutator is usually permanently integrated into the
rotor, so replacing it usually requires replacing the whole rotor.

        Large brushes are desired for a larger brush contact area to maximize motor output,
but small brushes are desired for low mass to maximize the speed at which the motor can run
without the brushes excessively bouncing and sparking (comparable to the problem of "valve
float" in internal combustion engines). (Small brushes are also desirable for lower cost.)
Stiffer brush springs can also be used to make brushes of a given mass work at a higher
speed, but at the cost of greater friction losses (lower efficiency) and accelerated brush and

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commutator wear. Therefore, DC motor brush design entails a trade-off between output
power, speed, and efficiency/wear.




        Fig.15 dc motors
A:shunt
B:series
C:compound
f = field coil

There are five types of brushed DC motor:

A. DC shunt wound motor

B. DC series wound motor

C. DC compound motor (two configurations):

       Cumulative compound
       Differentially compounded

D. Permanent Magnet DC Motor

E. Separately excited (sepex)

Brushless DC motors

        Some of the problems of the brushed DC motor are eliminated in the brushless design.
In this motor, the mechanical "rotating switch" or commutator/brushgear assembly is
replaced by an external electronic switch synchronised to the rotor's position. Brushless
motors are typically 85-90% efficient or more (higher efficiency for a brushless electric
motor of up to 96.5% were reported by researchers at the Tokai University in Japan in
2009),[17] whereas DC motors with brush gear are typically 75-80% efficient.

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          Midway between ordinary DC motors and stepper motors lies the realm of the
brushless DC motor. Built in a fashion very similar to stepper motors, these often use a
permanent magnet external rotor, three phases of driving coils, one or more Hall effect
sensors to sense the position of the rotor, and the associated drive electronics. The coils are
activated, one phase after the other, by the drive electronics as cued by the signals from either
Hall effect sensors or from the back EMF (electromotive force) of the undriven coils. In
effect, they act as three-phase synchronous motors containing their own variable-frequency
drive electronics. A specialized class of brushless DC motor controllers utilize EMF feedback
through the main phase connections instead of Hall effect sensors to determine position and
velocity. These motors are used extensively in electric radio-controlled vehicles. When
configured with the magnets on the outside, these are referred to by modellers as outrunner
motors.

          Brushless DC motors are commonly used where precise speed control is necessary,
as in computer disk drives or in video cassette recorders, the spindles within CD, CD-ROM
(etc.) drives, and mechanisms within office products such as fans, laser printers and
photocopiers. They have several advantages over conventional motors:

      Compared to AC fans using shaded-pole motors, they are very efficient, running
       much cooler than the equivalent AC motors. This cool operation leads to much-
       improved life of the fan's bearings.
      Without a commutator to wear out, the life of a DC brushless motor can be
       significantly longer compared to a DC motor using brushes and a commutator.
       Commutation also tends to cause a great deal of electrical and RF noise; without a
       commutator or brushes, a brushless motor may be used in electrically sensitive
       devices like audio equipment or computers.
      The same Hall effect sensors that provide the commutation can also provide a
       convenient tachometer signal for closed-loop control (servo-controlled) applications.
       In fans, the tachometer signal can be used to derive a "fan OK" signal.
      The motor can be easily synchronized to an internal or external clock, leading to
       precise speed control.
      Brushless motors have no chance of sparking, unlike brushed motors, making them
       better suited to environments with volatile chemicals and fuels. Also, sparking



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       generates ozone which can accumulate in poorly ventilated buildings risking harm to
       occupants' health.
      Brushless motors are usually used in small equipment such as computers and are
       generally used to get rid of unwanted heat.
      They are also very quiet motors which is an advantage if being used in equipment that
       is affected by vibrations.

        Modern DC brushless motors range in power from a fraction of a watt to many
kilowatts. Larger brushless motors up to about 100 kW rating are used in electric vehicles.
They also find significant use in high-performance electric model aircraft.




                            Fig.16 12V DC Toy motor




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      8. EXPERIMENTAL RESULTS
         In order verify the performance efficiency of the proposed ASAS, three cases were
involved to testify its working situation as follows.
Case 1: variation of vin over the control signal in the ac/dc switching system
         Based on the Vin (battery voltage) is varied from 11.6V to 13.6V, and its respective
control signal status is presented in Fig. . At the beginning, (S,R) is (0,1) when Vin is at
11.6V, and (S,R) becomes (0,0) when Vin is beyond 11.8V but below 12.6V. However, the
control signal (Q) is still at the low level (0) until V in reaches 12.6V. Whenever the control
signal switches to the high level (1), the load power changes its power connection from AC
source to the battery immediately. Once the load starts to consume the battery power, the
power connection will be remained until the battery voltage is down to 11.9V again.




                            Fig.17 Battery voltage over the control signal

Case 2: sunlight strength over shutter operation and sensor signals

        The sunlight strength over shutter operation and sensor signals are presented in Fig. .
Initially, the shutter is inactive because the sunlight is at the moderate condition, i.e., (VL,VH
) = (1,0). When the sunlight strength rises up beyond the high level, i.e., Vcds =4.11V,
(VL,VH ) changes to (0,0), and the motor thus pulls the shutter down until Vcds =3.9V. The
shutter will then remain inactive unless Vcds > 4.11V again. On the other hand, the sunlight
strength falls down below the low level, i.e., Vcds =3.8V, (VL,VH) changes to (1,1), and the
motor pulls the shutter up immediately until the moderate sunlight is reached,i.e., Vcds
=3.9V. Similarly, the shutter will then keep inactive unless Vcds < 3.8V again. During the


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moderate sunlight status, (VL,VH) remains (0, 1), and the motor is resting. Obviously, this
outcome confirms that the sunlight strength is always driven toward a moderate situation
(3.8V<Vcds < 4.11V).




                       Fig.18 Sunlight strength over shutter operation

Case 3: sunlight strength over blade operation and sensor signals

        In Fig. , it is found that initially (VL , VH) is (1,1) as Vcds> 4.11V. Therefore , the
shutter is pulled up for a short distance. Then, the blade close and open rotating action is
operated. This action continues until the sunlight reaches the moderate condition, i.e., (VL,
VH) = (1,0). When the sunlight is at the weak situation, (VL,VH) becomes (0,0). The shutter
is then pulled down for a short distance and the blade close and open rotating action is
operated to adjust the indoor sunlight amount.




                         Fig. 19 Sunlight strength over blade operation


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                                    9. APPLICATIONS
     Extends the green power applications and is very feasible for general facilities. The
       AC/DC switching system can connect the AC power immediately when the solar
       battery power is insufficient to support the entire system.
     It extends the scope for PWM based motor speed control.
     Better homecare services for patients.
     The proposed system can be simply extended to the green house environment for
       floriculture in office or building sunlight control.




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                                         10. CONCLUSION

        The automatic sunlight adjusting system for home care          using solar power is
presented in this paper. The AC/DC switching system can connect the AC power
immediately whenever the solar battery power is insufficient to support the system. This
mechanism in deed extends the green power applications and is very feasible for general
facilities that require no large power. The proposed system has also presented a local-loop
approach for real-time automatic shutter control operation. Various action signals determinate
by the sunlight detectors can be transmitted to the respective microprocessor that is to send
control signals for appropriate shutter and its blade operation.

Accordingly, moderate sunlight condition can be thus maintained properly. Actually,
practical examples have demonstrated that the proposed scheme can reach both rapid and
stable shutter action performance. Additionally , a reality of the multiple speed options has
made the proposed system working more smoothly. For further applications, the proposed
system can be simply extended to the green house environment for floriculture in office or
building sunlight control.




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                                11. REFERENCES
[1].Hsiung-Cheng Lin' , Chao-Hung Chcrr', Guo-Shing Huang' , Shin-Ming Chang'
“Development of Solar Power Based Automatic Sunlight Adjusting System for Home Care”
IEEE International Symposium on Industrial Electronics (ISlE 2009) Seoul Olympic Parktel,
Seoul, Korea July 5-8, 2009
[2]. C.H. Chen , H.e. Lin, Y.e. Liu, W.e. Hsu, S. M. Chang, "Sufficient Sunlight Supply for
Home Care using Local Closed-loop Shutt er Control System ", 2008 IEEE International
Conference on Systems, Man, and Cybernetics, 12-15 October, 2008 , Singapore, pp.2270-
2275.




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