Simple mobile signal detector circuit

A cell phone signal detector can detect the presence of an activated cell phone from a distance of about one and a half meters. Thus, the detector can be used to prevent the use of mobile phones in exams, in secret areas, etc. Also, this device can be useful in detecting a mobile phone in spying and unauthorized video transmission.
The scheme registers any transmission from the phone, be it an SMS, a voice call or an Internet connection. As soon as a radio carrier signal is detected, the circuit lights up. Light-emitting diode, signaling high-frequency oscillations.

Detector circuit

A conventional RF detector using an LC loop is not suitable for detecting signals in the GHz frequency band used in mobile phones. Mobile phone transmission frequencies range from 0.9 to 3 GHz with wavelengths ranging from 3.3 to 10 cm.
Here the circuit uses a 22p disk capacitor (C3) to capture radio signals from a mobile phone. The length of the antenna wire of the capacitor is fixed as 18 mm with a pitch of 8 mm between the terminals to obtain the desired frequency.The capacitor along with the antenna acts as a small gigahertz gamma antenna to collect radio signals from a mobile phone.

The CA3130 amplifier is used in the circuit as a current-to-voltage converter with capacitor C3 connected between its inputs. It is a version of CMOS that uses transistor-protected P-channel transistors on the gate at the input, providing very high input impedance, very low input current, and very high speed operation. The output CMOS transistor amplifies the signal and turns on Light-emitting diode.

Cell phone signal detector assembly

I assembled the detector on a printed circuit board. Pre-drafted, etched, tinned and drilled. In general, everything is as it should be.



In principle, a correctly assembled detector does not need adjustment and starts working immediately after switching on.
The only thing is that you can play around with the output antenna to obtain greater sensitivity of the circuit to the cell phone signal.



In the end I decided to add a buzzer by soldering it parallel to the LED.

Video

Original article in English