Cell Phone Detector circuit

Cell Phone Detector is a circuit that can sense the presence of any activated cell-phone nearby and gives an indication of activated cell-phone near around of it. Basically Cell-phone detector is a Frequency Detector or a Current to Voltage Converter Circuit which catches frequencies about 0.8 - 3.0GHz (Mobile band frequencies). RL tuned circuit (Resistor–Inductor circuit) is not suitable for detecting the RF signals in GigaHertz range.

This Mobile Detector Circuit can detect incoming/outgoing calls, messaging, video transmission and any SMS or GPRS uses within the range of 1 meter. This circuit is very useful to detect Cell-phones at Cell-phone restricted places like Exam halls, meeting rooms, hospitals etc. It is also useful in detecting the unauthorised use or spying using hidden Cell Phone. It can detect the RF Transmission from the Mobile Phone and triggers Buzzer to produce beep sound, even if the phone is kept on Silent mode and this alarm continues beeping till the presence of RF signals.

Required Components:

• Op-Amp CA3130
• 2.2M resistor (2)
• 100K resistor (1)
• 1K resistor (3)
• 100nF capacitor (4)
• 22pF capacitor (2)
• 100uF capacitor         
• Bread board
• 9 Volt Battery
• Battery Connector
• LED
• Transistor BC547
• Transistor BC557
• Connecting wires
• Buzzer
• Antenna

Circuit Explanation:

In this circuit we have used a CA3130 OP-Amp IC for detecting incoming or outgoing signal around it.  Op-amp non-inverting end is connected to Vcc through 2.2M resistor and it is also connected to the ground through 100K resistor and 100uF Capacitor. Its inverting terminal is feedback from its output through a 2.2M resistor for amplify the signal. Two 100nF capacitors are connected between inverting and non-inverting terminal, working as loop antenna for the system. Two 100nF capacitors are connected in series between Pin 1 and 8 of op-amp to boost the gain of the current to voltage converter at its output pin.

Output of this op-amp is connected at the base of NPN transistor namely BC547 through a 1k resistor and a LED is connected at its emitter for indication. A buzzer is also used for sound indication by using a PNP transistor namely BC557. And a 9 volt battery is used for powering the circuit. Rests of connections are shown in the Circuit Diagram below.

Working Explanation:

This circuit consist an op-amp with some active passive components. A LED and buzzer are used for indication of presence of cellphone. Op-amp is configured as Frequency Detector or Current to Voltage Converter and its output is connected to a LED and buzzer using NPN and PNP transistors.

Working of Mobile Detector is simple. Two 100nF capacitors (C2 and C3), in parallel, are used for detecting RF signal from Mobile Phone. These capacitors are working as loop antenna for the system. When there is any call or SMS then capacitors in parallel detect the data transmission frequencies or RF signal and output of op-amp goes high or low (fluctuating) due to generated current at the input side of op-amp. Due to these fluctuations, LED turns on and off through NPN transistor according to the signal’s frequency. Now PNP transistor is also triggered with the same frequency and buzzer starts beeping until data transmission gets finished. If you are not familiar with working of Op-amps then learn more about Op-amps here.