Here is a simple engineering project circuit of a handy mobile phone detector circuit (sniffer). The pocket-size mobile communication detector or sniffer can sense the existence of mobile. So you can use it to avoid the use of mobile phones in private rooms, examination halls, etc.
The circuit can detect incoming and outgoing calls, SMS, MMS, GPRS usage, and video transmission even when you set the mobile phone aside in silent mode. Here, the instant bug detects RF (Radio Frequency) transmission signal from a mobile phone, it produces a beep sound alarm.
Circuit Diagram of Mobile Phone Detector Circuit
Components Required of Mobile Phone Detector Circuit
- Resistors (100kΩ; 10kΩ; 15kΩ; 18kΩ x 2; 2.2kΩ; 56Ω x 2)
- Potentio meters (1MΩ; 22kΩ)
- Capacitors (47µF, 25V; 0.1µF; 10µF, 25V x 2; 100µF, 25V x 8; 4.7µF, 25V)
- Diodes (1N3491; 1N4148)
- Transistor BFR96
- IC TL071
- IC LA4440
- Loud speaker (8Ω, 6W)
- Areal (You can use a simple wire piece)
Working Priciple of Mobile Phone Detector Circuit
- This circuit can notice the use of GSM mobile phone in mobile restricted areas such as Examination hall or confidential rooms etc.
- It can sense the activity of mobile phone from a distance of 8 meters or more.
- The sniffer keeps monitoring the RF (Radio frequency) level in the region and gives warning if the RF level increases due to mobile phone activity.
- If you place two similar units of sniffers, the range is improvable.
- The circuit is able to detect all forms of mobile phone activity even when it is in silent mode. The circuit is designed as a sensitive RF detector. There, the RF signal diode 1N34 forms the major element.
- With the help of a resistor and a capacitor the signal diode picks up the RF energy in the area.
- In the standby mode, the output from the diode is around 0.6mV. It rises to 60mV in the presence of RF signal.
- Since the voltage from the sensor diode is too weak, three stages of amplification are required to give warning indication through speaker.
- Output signal from the diode is pre amplified by the transistor BFR96. It is a high frequency (Microwave frequency) low power transistor with huge current gain (approximately 15dB at 0.5GHz) and bandwidth.
- The pre amplified signal is fed to next amplifier stage built around IC TL071, it is a low noise JFET input op amp with low input bias and offset current. The biFET technology gives high slew rate to the IC.
- Here the TL071 is designed as an inverting amplifier; the inverting input of op amp receives the pre amplified signal from the first part.
- The Potentio meter can be adjusted to vary the gain of op amp circuit.
- The amplified signal is then passed through a capacitor and diode; with the help of this arrangement we can introduce more stages to extend the range.
- The next potentiometer is used to vary the signal amplitude, then it is fed to amplifier stage built around IC LA4440, it is a two channel audio power amplifier with inbuilt dual channels for stereo and bridge amplifier applications.
- In dual mode the IC LA4440 gives 6W, where as in bridge mode it provides 19W. It has good ripple rejection of 40dB, small residual noise, built in over voltage and surge voltage protection, and pin to pin protection.
- In our circuit this IC is wired as bridge mode with only one input.
- The loudness of the circuit can be adjusted by changing the potentiometer.
- When the mobile phone is activated within the range of eight meters, a loud motor sound is heard through the speaker.
- Use good quality 8Ω, 6W speaker in order to get clear warning sound.
- The RF reception and performance of the circuit is dependent on many factors such as output power from the mobile device, orientation and position of the cell phone.
On an interesting note, the mobile phone detector circuit is also useful for detecting the use of the mobile phone for spying and activities.