project14 final paper

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					  Cell Phone
Controlled Audio
  Mute Switch
           by
     Baldwin Yeung
      Kavita Nagpal
       Vivek Patel
         ECE 445
    T.A. Ishaan Gupta
    Date: 12/05/2005
   Project Number # 14




            1
                                   ABSTRACT

We designed and created a project in which a detector circuit detects the electro-magnetic
field radiated from an incoming call to a cell phone to control the functioning of an audio
system. The designed circuit automatically disconnects power supply to the audio system
whenever a call is received or made by the cell phone.
        The device uses a cluster of inductors to detect the EMF radiated by the cell
phone receiver when an incoming call occurs. This signal is amplified to trigger a
monostable timer circuit. The output of the timer circuit is feed through a relay to the
audio system.
        Although our project worked as expected, there are some improvements that can
be made to make the detector circuit more sensitive. Instead of using a cluster of
inductors, we can use less number of inductors to make the circuit more compact and
small.
        One of the major advantages of our project is that it is less costly than the detector
circuits available in the market today, such as the Motorola Bluetooth detector which
costs about $200.




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                                              TABLE OF CONTENTS

1.   INTRODUCTION ....................................................................................................................1
     1.1 Purpose ...............................................................................................................................1
     1.2 Specifications ......................................................................................................................1
     1.3 Subprojects .........................................................................................................................1
         1.3.1 Cell Phone Incoming Call Detector ...........................................................................2
         1.3.2 Cell Phone Removal Detector ...................................................................................2
         1.3.3 Logical Module .........................................................................................................2
         1.3.4 Audio Mute ...............................................................................................................2
         1.3.5 Audio Device .............................................................................................................2

2.   DESIGN PROCEDURE ...........................................................................................................3
     2.1 Cell Phone Incoming Call Detector ....................................................................................3
     2.2 Cell Phone Removal Detector ............................................................................................3
     2.3 Logical Module ...................................................................................................................3
     2.4 Audio Mute .........................................................................................................................3
     2.5 Audio Device ......................................................................................................................3

3.   DESIGN DETAILS ..................................................................................................................4
     3.1 Cell Phone Casing...............................................................................................................4
     3.2 Cellular Phone Calling Detector .........................................................................................4
     3.3 Audio Mute Switch .............................................................................................................4
     3.4 Speakers and IPOD .........................................................................................................4, 5
     3.5 Audio Device ......................................................................................................................5

4.   DESIGN VERIFICATION .......................................................................................................6
     4.1 Testing ................................................................................................................................6
         4.1.1 Incoming Call Detector .............................................................................................6
         4.1.2 Cell Phone Removal Detector ...................................................................................6
         4.1.3 Logic ..........................................................................................................................6
         4.1.4 Audio Mute................................................................................................................6
         4.1.5 Audio Device .............................................................................................................6

5.   COST ........................................................................................................................................7
     5.1 Parts ....................................................................................................................................7
     5.2 Labor ...................................................................................................................................7

6.   CONCLUSIONS ......................................................................................................................8

7    REFERENCES .........................................................................................................................9

     APPENDIX A – BLOCK DIAGRAM ...................................................................................10

     APPENDIX B – FUNCTIONAL DIAGRAM .......................................................................11




                                                                 iii
APPENDIX C – SCHEMATICS ...............................................................................12, 13, 14

APPENDIX D – MONOSTABLE MODE.............................................................................15

APPENDIX E– TESTS .............................................................................................16, 17, 18,

APPENDIX F – WAVEFORMS .............................................................................19,20,21,22

APPENDIX G – PARTS AND COST ...................................................................................23




                                                   iv
v
                                  1. INTRODUCTION

We designed and created a project in which a detector circuit detects the electro-magnetic
field radiated from an incoming call to a cell phone to control the functioning of an audio
system. The designed circuit automatically disconnects power supply to the audio system
whenever a call is received or made by the cell phone.
        The device uses a cluster of inductors to detect the EMF radiated by the cell
phone receiver when an incoming call occurs. This signal is amplified to trigger a
monostable timer circuit. The output of the timer circuit is feed through a relay to the
audio system.
        This project includes two important circuits and a cell phone holder. The first is
the cellular phone detector circuit and the second is the controlled audio mute switch. The
detector circuit has an LED that lights up when an incoming call is received and it also
sends the signal to the mute switch. The cell phone holder has a switch and an array of
LEDS that are always on. Using the switch, the LEDS can be turned off whenever the
cell phone is not placed on the holder. This means that the audio system will always be
muted unless the phone is placed on the holder. The mute switch receives the signal
either from the holder or the detector circuit to turn off (mute) the audio system.

1.1 Purpose
The purpose of this project was to use our knowledge of electro-magnetic theory, power
circuits and digital system design to design a cost effective detector circuit. We chose this
project for two significant reasons. The primary reason is that no important calls can be
missed with this circuit. The second reason is the inconvenience and safety issue of
having to turn off the audio system while driving a car.

1.2 Specifications
The project is split into 5 different modules.
The device has to pick up incoming phone calls and detect if the cell phone is in the
casing. When the phone is in the casing, and there are no incoming calls, the audio
system acts normally. Due to the fact that cell phones emit EMF, the device will pick up
the signal and automatically disconnects the power to the audio system. Cell phones emit
a frequency between 850 MHz and 1.2 GHz. Since the voltage across inductor is given
            dI
by V  L  , the time varying EMF will activate the circuit.
            dt
An LED and a photodiode is used to determine if the phone is in the casing. A transistor
in conjunction with the inductors is used to amplify the signal to trigger the 555 timer
chip which requires a minimum of 2.7V. The audio system is fed through a relay which
would either connect or disconnect the voltage between the amplifier and the speaker.

1.3 Subprojects
The project was split into 5 modules, which each perform specific tasks.

1.3.1 Cell Phone Incoming Call Detector
This module was used to pick up the EMF emitted from a phone receiver. A transistor is
used to step up the voltage to trigger the logical module.


                                             1
1.3.2 Cell Phone Removal Detector
This module is used to determine if the cell phone is in the casing. The use of an LED
and the photodiode required testing of distance and ambient light.

1.3.3 Logical Module
This module was designed to perform an OR operation between the cell phone removal
detector and the cell phone incoming call detector. Additionally, a 555 timer is used to
elongate the high signal from the incoming call detector up to 5 – 6 seconds.

1.3.4 Audio Mute
This module consisted of a relay between the amplifier and the speakers. Depending on
the signal from logical module, it connects or disconnects power between the amplifier
and the speakers.

1.3.5 Audio Device
This device consisted of an Ipod, amplifier and a computer speaker. It can be modified to
be used for car audio or home entertainment system.




                                            2
                               2. DESIGN PROCEDURE

2.1 Cell Phone Incoming Call Detector Design
This was designed to pick up the incoming signal from a cell phone. Through testing we
discovered that older cell phones emit more EMF than new cell phones. We also
discovered that the EMF emitted was strongest at the cell phone’s speaker end. Initially,
we designed the circuit using two 10mH inductors. However, this produced poor results
due to the lack of sensitivity of the inductors. Hence, this problem was rectified by
replacing the two 10mH inductors by six 3.3mH in a 1  1 inch area. By increasing the
surface area of the inductance, the inductors became more sensitive to the EMF emitted
from the phone. A transistor was used to amplify the signal picked up by the inductors to
activate the 555 timer chip.

2.2 Cell Phone Removal Detector Design
This was designed by using a white LED and a photodiode to detect the removal of the
cell phone from the casing. During our testing we determined that the white LED was the
most accurate in being detected up to a distance of 5 cm. The photodiode used was
compatible in the sense that it didn’t sensed ambient light interference.

2.3 Logical Module
This was designed to perform two operations. First, it was designed to be used in a
monostable operation mode to disconnect the power to the audio system for a time period
of at least 7-8 seconds. Second, it was designed to operate in an OR gate operation
between the incoming call detector circuit and the removal detector circuit. The input of
the 555 timer was used to distinguish between the signals from the incoming call detector
or the removal detector. The output from the timer is fed through a relay to the audio
device.

2.4 Audio Mute Design
This device is essentially just a relay. It was designed to control the power supply to the
audio system. The amplifier and the speaker’s ground connection are common. The lead
of the amplifier is plugged in to one end of the relay. The remaining lead of the speaker is
connected to the other end of the relay. This would complete the relay circuit.

2.5 Audio system Design
In order to create an audio device, we connected an Ipod to an amplifier which in turn
was connected to a computer speaker.




                                             3
                                  3. DESIGN DETAILS


3.1 Cellular Phone Incoming Call Detector

This circuit is designed to detect incoming calls in a cell phone even when the calling
tone of the device is switched – off. The circuit uses a sensor coil L1 to detect the
magnetic field given off from the cell phone receiver when an incoming call occurs.
Capacitor C1 is a 63 V polyester capacitor. This is used in blocking, by passing, filtering,
timing, interference suppression, low pulse applications. The transistor Q1 amplifies the
detected signal from the sensor coil and drives the monostable input pin (2) of the 555
timer chip. Pin 4 and pin8 are connected to the 5 volt battery. The output voltage
measured across pin 3 is doubled by the capacitor C2 and the Schottky – barrier diode D2
to drive the ultra bright LED. This LED is connected to the LED 3 on the cell phone
casing.

3.2 Cell Phone Removal Detector

The casing has two LEDs and a switch on the front panel. The first LED indicates if the
audio device is ON and the second LED indicates if the audio device is OFF. The switch
activates our device and is also connected to a third LED inside the casing. When the
switch is turned ON, the third LED is turned ON. This LED is used to determine if the
cell phone is placed in the casing or displaced from the casing. It is used in conjunction
with a photo-transistor, which sends a signal to the audio mute switch to be activated
when it detects a light from the LED.


3.3 Logical Module

We used an LM555 timer to control the relay in the audio mute device. It was supplied
with a 5V Vcc. According to the datasheet, it required a minimum of 2.7V at the input to
trigger the output. In order to hold the high signal for at least 7-8 seconds to compensate
for the oscillating frequency signal from the incoming call detector, capacitor was used at
pin 6. From the monostable mode (Appendix C), we used the following equation to
determine the value of the capacitor to hold the signal for 7-8 seconds.
                        T  1.1 R  C , where the value of R = 800K.


3.4 Audio Mute Switch

This circuit automatically disconnects power supply to an audio system whenever the
mobile handset is lifted off the holder. The circuit is wired around IC LM555. LM555 is
the CMOS version of the timer NE555. It is used as a medium-current line driver with
either an inverting or non-inverting output. The Audio system is connected to the circuit
via normally opened (N/O) contacts of the relay.




                                             4
When the cell phone is in its holder, LDR1 does not receive any light from white LED1
and its resistance is high. As a result, the voltage at pin 2 of IC1 remains high to provide
a low output at pin 3. The low output of IC1 activates relay RL1 and the audio system
gets power supply via its N/O contacts. LED3 glows to indicate that the audio system is
ON.

When the handset is taken off the holder, light rays from LED1 fall on LDR1 and its
resistance decreases. As a result, the voltage at pin 2 of IC1 decreases to provide a high
output at its pin 3. The high output of IC1 deactivates relay RL1 and the audio/video
system does not get power supply. LED2 glows to indicate that the audio/video system is
OFF.

Preset VR1 is used to control the sensitivity of the circuit. Zener diode ZD1 is used for
protecting white LED1 from the higher voltage. The circuit works off a 5V car battery.
Switch S1 can be used to manually switch on/off the audio system.


3.5 Audio Device

In order to create an audio device, we connected an Ipod to an amplifier which in turn
was connected to a computer speaker.




                                              5
                             4. DESIGN VERIFICATIONS

The design of the device was based heavily the inductors ability to pick up the emf of the
cell phone. We tested the multiple distances at which the cell phone could be placed to
see if the inductors would pick up the EMF from an incoming call. The accuracy of the
led detector on our casing was tested to make sure ambient light would not trigger the
device. Finally the delay at the logic module was tested for appropriate length.

4.1.1 Incoming Call Detector

Multiple distances between the phone and inductors were tested for the strength of signal
picked up by the inductors. The data concluded that if the cell phone was held more than
6 centimeters from the inductor the signal detected was too weak to generate an adequate
amount of voltage to the logic module. Data from a Motorola V551 and LG4050 is
displayed in Appendix D and E. Waveforms of the sensitivities of the inductors at
different distances are displayed in Appendix E. As testing began it was realized that a
strength of signal was dependent on proximity to the speaker part of the phone. Thus all
tests were completed with the speaker side of the phone facing the inductors.

4.1.2 Cell Phone Removal Detector
Different color LED’s produced different results in the photodiode’s ability to detect
light. As a result the green, red, and yellow LED’s did not consistently give an accurate
reading to the photodiode up to 6cm. However the use of a white LED gave us the best
result in light detection. Despite ambient light the detector was able to correctly detect the
light from the white LED when it was shown on it. The value 6cm’s was tested due to the
fact most cell phones are between 2-3cm.

4.1.3 Logic
A value of 7-8 sec delay was achieved by placing a 1μF capacitor at pin 6 on the LM555
timer. The delay was tested to be accurate even when the cell phone was moved further
away from the inductor to the point of 6cm.

4.1.4 Audio Mute
The audio mute device was a relay with the amplifier attached at one end and speaker at
the other end. As expected the relay connected the two devices depending on the signal
generated by the timer. The relay required a 5V VCC.

4.1.5 Audio Device
The audio device was tested initially by hooking an Ipod to an amplifier and the amplifier
was attached to a computer speaker. This worked as designed.




                                              6
                                        5. COST
5.1 Parts

Our final product’s estimated cost is $29.90. We plan to market the product at $50.

5.2 Labor

We estimated our future salary at around $20 per hour. The amount of time spent
developing and researching the circuit turned out to be approximately 50 hours.

LABOR: $20/hour x 2.5 x 50 hours x 3 people = $7,500.
PARTS: $29.90
Grand Total = 29.90 + 7500 = $7,529.90
To break even, we need to sell 375 devices.
Each device makes a profit of ($50 - $ 29.90 =) $20.10. The product that is currently in
stores is called Motorola Bluetooth Car-Kit that sells for $209.99. So all in all, our
product is extremely cost efficient. However, we are not in direct competition with
Motorola because their Bluetooth product performs a host of other functions while our
device has the major function of turning off the audio system as a cell phone receives a
call.




                                            7
                                   6. CONCLUSIONS

We were extremely satisfied with the operation of our project. The Audio mute was
activated in a timely fashion. Another great advantage of the circuit was that the audio
mute circuit is activated even when the cell phone is in silent or vibrate mode. The cell
phone detector circuit also operated as expected.

There were a couple of challenges that were faced during project implementation. The
Audio remained turned off for only 3-5 seconds when the phone rang. We used a 1μF
capacitor connected to our timer o overcome this problem. Another big challenge was the
distance issue. The sensitivity of the circuit decreased as the phone was taken further
away from L1 (Inductor cluster).

There are a number of future enhancements that could be done to make the product more
marketable and business-friendly.
    The sensitivity of the device should be increased. Instead of placing the inductors
       all in one place, they should be placed at strategic locations like the seat belts.
    The problem of noise interference can be tackled by using band filters.
    Ambient Light Interference is another problem that can be addressed. Instead of
       using and LED and LED sensor, a proximity sensor can be used.
    More amplification can be used to get higher sensitivity from even smaller
       signals.
    The device can also be made more cost effective. The finished product wouldn’t
       have the mounting hardware. When orders are produced in bulk, the cost is cut
       drastically. We also combined 2 modules on a single board to make it more
       efficient.
    We implemented the circuit using a 5V power supply. Since the car has a 12 V
       supply, the values of the resistances and capacitances will have to be modified
       accordingly.
    FCC regulates the amount of EMF a phone can safely emit. Our device works on
       the principle of EMF radiated by a cell- phone; thus to make the product
       compatible with phones of the future, the circuit should be more sensitive.




                                             8
Reference:

N. N. Rao, Elements of Engineering Electromagnetics, 5th ed., Prentice-Hall, 1999.




                                         9
Appendix A-Block Diagram




  Cell Phone
  Incoming Call
  Detector
                           Logical   Audio Mute
                           Module
  Cell Phone
  Removal Detector



                                     Audio Device




                               10
Appendix B-Functional Diagram




                                11
Appendix C (i)




                 12
Appendix C (ii)




                  13
Appendix C (iii)




                   14
Appendix D – Monostable Mode




                               15
Appendix E – Tests (i)




Motorola V551




                         16
Appendix E – Tests (ii)




LG 4050




                          17
Appendix E-test(iii)

 Frequency (MHz)                  Voltage (mV)   Distance
       96.3                            15          6 cm
       97.7                           16.2       Phone off
      153.8                           47.8         1 cm
       880                            79.4         0 cm




                                           Frequency Vs. Voltage

                           1000
    Frequency (MHz) ....




                           800

                           600

                           400

                           200

                             0
                                  96.3              97.7            153.8   880
                                                         Voltage (mV)




                                                        18
Appendix F – Waveforms


(i) Phone OFF




                         19
Appendix F – Waveforms

(ii) Phone at a distance of 0cm from L1




                                          20
Appendix F – Waveforms

(iii) Phone at a distance of 1 cm from L1




                                            21
Appendix F – Waveforms

(iv) Phone at a distance of 6 cm from L1




                                           22
Appendix G – Parts and Costs

Part               Quantity    Unit Price ($)   Subtotal ($)
Inductor Coil      1           2.00             2.00
1N5819             1           1.00             1.00
BC547              1           1.00             5.00
Capacitors         5           0.50             2.50
Resistor           6           0.10             0.60
5 Volt Battery     1           2.00             2.00
LED                4           0.20             0.80
1N4007             1           1.00             1.00
SK100              1           1.00             1.00
LM555              1           5.00             5.00
Switch             1           2.00             2.00
Box                1           5.00             5.00
LED Light Sensor   2           1.00             2.00
Total                                           29.30




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