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Here's the link:https://www.electronicsforu.com/electronics-projects/mobile-phone-detector-using-lm358 , i'm trying to do this as a project for my classes, it's supposed to light up the diode when cell phone is dialing.Please post a link to the source of the circuit. As shown it will not do anything. Assuming that ANT.1 is an RF signal, that signal will be shunted to the power ground by C1 and shunted to the circuit reference by C2. The output at pin 1 will sit at approx 1.5 V. The voltage across the LED will be less than 1.0 V, not nearly enough to cause it to illuminate.
My guess is that the circuit is acting as a comparator or AM detector. The problem is that a 358 is a relatively slow and low-gain part. It can barely amplify audio, let alone RF.
If what is coming in ANT.1 already is amplitude detected and coming from a low-to-medium-impedance output stage of something and is a large enough signal, then this circuit will do something. Note that there are three *big* IFs, and all must be true.
BUT - given the number of cell phones everywhere, and the fact that all of them are transmitting almost constantly whether or not anyone is actually talking into them, what is it you are trying to achieve?
ak
It just might do that, if it's very close to the phone and if C1 and C2 are both rubbish capacitors with a high enough equivalent series resistance.it's supposed to light up the diode when cell phone is dialing.
Do you think this one might be better https://circuits-diy.com/how-to-make-a-simple-mobile-phone-call-detector-circuit/ ? or https://www.electronicshub.org/cell-phone-detector-circuit/It just might do that, if it's very close to the phone and if C1 and C2 are both rubbish capacitors with a high enough equivalent series resistance.
The LM358 per se is good for < 1 MHz only. I guess the RF is rectified and thus demodulated at the input protection circuit of the opamp or possibly by the input transistors themselves. The demodulated signal in the audio range is then amplified and used to drive the LED.I'm still struggling with an LM358 amplifying a 9.0-to- 2.4 GHz signal, but it appears to be all the rage.
I would not straightforwardly deny the possibility of this circuit to do what it is supposed to do.The circuit in this thread does not work because it was designed or copied by a kid in India who has not learned any electronics yet.