Electronic Spy Bug Circuit

Here we`ll discuss how to make an electronic spy bug circuit using two methods, one that consists of wire link from the transmitter to the receiver, and the other which is completely wireless and can be used to eavesdrop a particular conversation over a range of about 30 meters, over an ordinary FM radio. The circuit is basically a high gain ampli
Electronic Spy Bug Circuit - schematic

fier using the IC 741 as the heart of the circuit and also a couple of high gain output transistors. The IC 741 if configured as a non inverting amplifier which performs the function of a pre-amplifier stage. The gain of this IC 741 preamplifier stage may be varied as desired, using the pot across its input and output pin outs. The gain setting is used to set the sensitivity of the amplifier and is set to maximum so that even low volume speech conversation may be picked through it. The mic at the input transforms sound vibrations into minute electrical pulses, which is further amplified by the IC 741 to suitable levels before applying it to the output amplifier stage consisting of a standard push-pull stage. The purpose of this circuit is also the same as above, that is for catching weak sound signals or for hearing some hidden conversation, however the caught voice signals here is transmitted into the air instead of forwarding it through wire links. The frequency mainly depends on the positioning and the values of the inductor, C1, C2 and C3. The coil turn distance and diameter may be manipulated a little for optimizing best response over the FM receiver. A small antenna in the form of a 3 inches wire may be attached at the shown point for making the bug  highly responsive and generate distortion free signals. For the 741 circuit, the speaker is only positioned and used as the receiver and may be placed in some other...

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