IC 741 Transmitter Using Wire Connection

 

IC 741 Transmitter Using Wire Connection

In the above section we earned about wireless FM transmitter, if you are also interested to know how to make wired transmitter, in which voice could be transmitted through wires into a loudspeaker, then the following design may help

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. This push pull stage is made using a couple of high gain transistors 187/ 188.

Here, the signal received from the 741 output is suitably amplified so that it finally becomes audible over the speaker.

For the 741 circuit, the speaker is only positioned and used as the receiver and may be placed in some other room, where the eavesdropping may be intended to be carried out.

The linking of the speaker from the amplifier circuit may be done through wire connections, preferably by using thin wires and escorting the entire length up to the speaker in some hidden way, probably by laying it under the carpet or across the corners of the room.

For the wireless spy transmitter circuit everything becomes pretty simple and you just have to hide the transmitter circuit in some suitable place, like under the table, couch, sofa etc.

Parts List

• R1 = 10K,
• R2 = 10k,
• R3, R4 = 27K,
• R5 = 1.5 M,
• C1 = 104,
• C2 = 220uF/25V,
• T1 = 188,
• T2 = 187,
• MIC = electret mic,
• IC1 = 741,Power = 9 volt battery
• Headphone = 64 Ohms, or a small speaker of 8 Ohms, 2 inches