detect cell phones in examination halls, private rooms or finding a lost cell phone etc.
When we dial a number from our cell phone or send SMS and press the send button then our cell phone starts producing an RF signal to connect from the nearest tower. The circuit shown here will detect this RF signal in both incoming and outgoing call or SMS conditions and produces a beep sound.
The circuit is using two 1N34 germanium diodes for detecting the signal, two NPN 2N4401 transistors for amplifying the signal and an audio amplifier IC TDA2822M to drive a loud speaker. The gain of the circuit can be adjusted with 20K variable resistor. The 10K variable resistor is used to adjust the volume of the circuit.
The circuit can be operated from 9 to 12 volt DC. You can also use a 9 volt battery or 3 lithium coin size batteries and fit the hole circuit in a small box to make it handy and portable.
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Here is a very interesting and useful project of a sensitive cell phone detector circuit or we can also say it cell phone finder, sniffer or calling detector. The circuit is able to detect a cell phone from more than 10 feet away. The circuit can be used for a variety of purposes, for example it can be use to
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