Mobile Phone Detector Using LM358

By Kumar Abhisekh

12
16501

This mobile phone detector can sense the presence of an activated mobile phone from a distance of four to five metres. So it can come handy in an examination hall or meetings where mobile phones are not permitted.

The circuit can detect incoming and outgoing calls, SMSes, Internet and video transmissions even if a mobile phone is kept in silent mode. When it detects an RF signal from an activated mobile phone, its LED starts blinking and continues to blink until the signal stops. The author’s prototype is shown in Fig. 1.

mobile phone detector prototype
Fig. 1: Author’s prototype (a) when a call is not detected and (b) when a call is detected

Circuit and working

Circuit diagram of the mobile phone detector using LM358 is shown in Fig. 2. It is built around LM358 (IC1) and npn transistor BC548 (T1).

Circuit diagram of the mobile phone detector
Fig. 2: Circuit diagram of the mobile phone detector

When a mobile phone is active, it radiates RF signal that passes through nearby space. The signal contains electromagnetic RF radiation from the phone.

Capacitor C1 is used in the circuit to detect the RF signal from the mobile phone. When the mobile phone radiates energy in the form of RF signal, C1 absorbs it and passes on to the inputs of IC1. This is indicated by the flashing of LED1. Preset VR1 (2.2M) is used to vary the range of the circuit. Transistor T1 is used to amplify the signal obtained at pin 1 of IC1.
The circuit is applicable for 2G networks, GPRS and network search (manual/automatic). It does not detect 3G, WCDMA and HSDPA network signals so well.

Construction and testing

An actual-size, single-side PCB layout for the mobile phone detector circuit is shown in Fig. 3 and its component layout in Fig. 4. After assembling the circuit on the PCB, enclose it in a suitable plastic box.

Actual-size PCB layout for the mobile phone detector circuit
Fig. 3: Actual-size PCB layout for the mobile phone detector circuit
Component layout of the PCB
Fig. 4: Component layout of the PCB

Download PCB and component layout PDFs: click here

The circuit works off a 4.5V DC power supply.


Kumar Abhisekh is an electronics hobbyist

 

12 COMMENTS

  1. WANTS TO MARKETING OF YOUR PRODUCTS, i.e. GENERATION OF NEW BUYER’S, SO OUR SELL WILL INCREASE. EXPERINECE OF 20 YEARS IN FIELD MARKETING.

  2. Sir, plss tell me what if in case the mobile phone is neither receiving message or calls nor the data is turned on..In this scenario the person is using the phone but it won’t be detected by our detector..Is there any other circuit which will sense the mobile network..Nd also something which will sense the presence of a mobile phone which is on flight mode?

    • The circuit will not detect your mobile phone if it is not activated in normal mode or working mode. It will not detect in flight mode because this circuit can detect mobile phone only through its incoming and outgoing signals.

  3. Why it does not work well for 3G whereas 3G is also an RF signal like 2G ? And modifications in it can make it work for 3G also…?

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