Submitted By:
PRAVESH JAIN
PIYUSH JAIN

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• A light-emitting diode (LED) (pronounced /ˌɛl.iːˈdiː/[1], or just /lɛd/) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962,[2] early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
• The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection.[3]
• LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliance. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current LED products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output.
They also enjoy use in applications as diverse as replacements for traditional light sources in automotive lighting (particularly indicators) and in traffic signals. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology
• I-V diagram for a diode an LED will begin to emit light when the on-voltage is exceeded. Typical on voltages are 2-3 Volt
• Efficiency and operational parameters
• Typical indicator LEDs are designed to operate with no more than 30–60 milliwatts [mW] of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt [W]. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.
• One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a luminous efficacy of 18–22 lumens per watt [lm/W]. For comparison, a conventional 60–100 W incandescent lightbulb produces around 15 lm/W, and standard fluorescent lights produce up to 100 lm/W. A recurring problem is that efficiency will fall dramatically for increased current. This effect is known as droop and effectively limits the light output of a given LED, increasing heating more than light output for increased current.
• In September 2003, a new type of blue LED was demonstrated by the company Cree, Inc. to provide 24 mW at 20 milliamperes [mA]. This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006 they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Also, Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescents and better even than standard fluorescents.[25] Nichia Corporation has developed a white LED with luminous efficiency of 150 lm/W at a forward current of 20 mA.
• It should be noted that high-power (≥ 1 W) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA. The highest efficiency high-power white LED is claimed[27] by Philips Lumileds Lighting Co. with a luminous efficacy of 115 lm/W (350 mA)
• Note that these efficiencies are for the LED chip only, held at low temperature in a lab. In a lighting application, operating at higher temperature and with drive circuit losses, efficiencies are much lower. United States Department of Energy (DOE) testing of commercial LED lamps designed to replace incandescent or CFL lamps showed that average efficacy was still about 31 lm/W in 2008 (tested performance ranged from 4 lm/W to 62 lm/W)[28].
• Cree issued a press release on November 19, 2008 about a laboratory prototype LED achieving 161 lumens/watt at room temperature. The total output was 173 lumens, and the correlated color temperature was reported to be 4689 K.[29][unreliable source?]
White light
• There are two primary ways of producing high intensity white-light using LEDs. One is to use individual LEDs that emit three primary colors[44] – red, green, and blue, and then mix all the colors to produce white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works.
• Due to metamerism, it is possible to have quite different spectra which appear white.
• LM317 is the standard part number for an integrated three-terminal adjustable linear voltage regulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output voltage between 1.25V and 37V. A typical current rating is 1.5A although several lower and higher current models are available. Variable output voltage is achieved by using a potentiometer or a variable voltage from another source to apply a control voltage to the control terminal. LM317 also has a built-in current limiter to prevent the output current from exceeding the rated current, and LM317 will automatically reduce its output current if an overheat condition occurs under load. LM317 is manufactured by many companies, including National Semiconductor, Fairchild Semiconductor, and STMicroelectronics.
• Although LM317 is an adjustable regulator, it is sometimes preferred for high-precision fixed voltage applications instead of the similar LM78xx devices because the LM317 is designed with superior output tolerances. For a fixed voltage application, the control pin will typically be biased with a fixed resistor network, a Zener diode network, or a fixed control voltage from another source. Manufacturer datasheets provide standard configurations for achieving various design applications, including the use of a pass transistor to achieve regulated output currents in excess of what the LM317 alone can provide.
• LM317 is available in a wide range of package forms for different applications including heatsink mounting and surface-mount applications. Common form factors for high-current applications include TO-220 with part number LM317T and TO-3 with part number LM317K. LM317 is capable of dissipating a large amount of heat at medium to high current loads and the use of a heatsink is recommended to maximize the lifespan and power-handling capability.
• LM337 is the negative voltage complement to LM317 and the specifications and function are essentially identical, except that the regulator must receive a control voltage and act on an input voltage that are below the ground reference point instead of above it.

Presented by
Baldwin Yeung
Kavita Nagpal
Vivek Patel

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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.