CELL PHONE DETECTOR

It is the most common electronics equipment used in the cell phones. With the advancement in communication technology, the requirement of the cellphone has been increased the manifold. A cell-phone typically transmits and receives the signal in the frequency ranges of 0.9 to 3GHz. This article provides a simple circuit which can detect the presence of an activated cell phone by detecting these signals.

 

PRINCIPLE


The circuit behind this project is based on the principle of using a Schottky diode to detect the cell phone signal. The mobile phone signal is lying in between the frequency ranges in between of  0.9 to 3GHz. The Schottky diode has a unique property of being able to rectify the low-frequency signals, with the low noise rate. When an inductor is placed near the RF signal source, then it receives the signal through the mutual induction. Then the signal is rectified by the Schottky diode. This is the low power signal can be amplified and used to power any inductor like a LED in this situation.

 

CIRCUIT DIAGRAM


 

cellphone-detector-550x257

 

 

COMPONENT


  • LED = Blue LED
  • V1 = 12V
  • R6 = 10 Ohms
  • L1 = 10uH
  • IC1= LM339
  • R1 = 100Ohms
  • R5 = 100 Ohms
  • R4 = 200 Ohms
  • R3 = 3K
  • C1 = 100nF
  • Q1 = BC547
  • R2 = 100K

Cell Phone Detector Circuit Design:

Cell Phone Detector Circuit Design:

The detector circuit consists of an inductor, a diode, a capacitor and a resistor. Here an inductor value of 10uH is chosen only. A Schottky diode BAT54 is then chosen as the detector diode, which can rectify low frequency the AC signal. The filter capacitor is then chosen in a 1oonF ceramic capacitor, it is used to filter out the AC ripple. A load resistor of the 100 Ohms is used.

Amplifier Circuit Design:

Here a simple BJT BC547 is used in the common emitter mode. Since the output signal does have the low value, the emitter resistor is not required in this case. The collector resistor value is then determined by the value of battery voltage, then the collector-emitter voltage and the collector current. Now the battery voltage is chosen to be 12 V (since maximum open source collector-emitter voltage for BC 547 is 45V), the operating point collector-emitter voltage is 5 V and the collector current is 2 mA. This gives a collector resistor an approx of 3 K. Thus a 3 K resistor is used as Rc. Then the input resistor is used to provide bias to the transistor and it should be of larger value, so as to prevent the flow of the maximum current. Here we can choose a resistor value of 100 K.

 

Mobile Phone Tracking Circuit Operation:

In the normal condition, when there is no RF signal available, then the voltage across the diode will be negligible. Even though this the voltage is then amplified by the transistor amplifier, yet the output voltage is less than the reference voltage, which is  now applied to the inverting terminal of the comparator. Since the voltage at a non-inverting terminal of the OPAMP is less than the voltage at the inverting terminal, the output of the OPAMP is now a low logic signal.

 

APPLICATIONS


  1. This circuit can be implemented in the various areas like it can be used at examination halls, meetings to detect a presence of mobile phones and prevent the use of cell phones.
  2. It can be used for detecting the mobile phones and are used for spying and can also check the  unauthorized transmission of audio and video.
  3. It can also be used to detect the stolen mobile phones is a major problem with the people.

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