# cell phone detector circuit

i have successfully implimented below circuit for active cell phone detection but i dont seem to understand the working of this circuit,if someone could explain it would be a great help.Thank you.

• I think they work as huge gain amplifiers. So antenna picks some electricity, charges c2 a little which than is amplified and produces some voltage difference which lights the led. – Darko Mar 22 '16 at 16:22
• It's not specifically a cell phone detector - it will likely detect any reasonably sized electric field of almost any reasonable frequency thus making it an electric field detector. Is this what you wanted to build? – Andy aka Mar 22 '16 at 17:33
• The LM358 has a unity-gain bandwidth of only about 0.7 MHz, so in this case it's not really used to amplify the GHz signal from the antenna. See this answer for further speculation and a potentially "real answer" to this question. – uhoh Aug 5 '17 at 7:02

• R3 is the amplifier feedback resistor but the usual inverting mode input resistor is missing. Therefore the input antenna will provide alternating current to the virtual earth of the inverting input. For every nA of current flowing towards the inverting input the output will decrease by $1~nA \cdot 6.8~M\Omega = 6.8~mV$ (to keep the inverting input at the same potential as the non-inverting input).