20-04-2011, 12:16 PM
Presented by
Baldwin Yeung
Kavita Nagpal
Vivek Patel
[attachment=12458]
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.
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 by , the time varying EMF will activate the circuit.
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.
1.3.2 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. 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. 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.
, 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.
Baldwin Yeung
Kavita Nagpal
Vivek Patel
[attachment=12458]
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.
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 by , the time varying EMF will activate the circuit.
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.
1.3.2 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. 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. 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.
, 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.
