doorphone intercom

Posted on Feb 5, 2014

An 8 ohm speaker is used both as a microphone and also an output device. The BC109C stage amplifies in common base mode, giving good voltage gain, whilst providing a low impedance input to match the speaker. Self DC bias is used allowing for variations in transistor current gain. An LM386 is used in non-inverting modeas a power amplifier to boost voltage gain and drive the 8 ohm speaker.

doorphone intercom
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The 10k potentiometer acts as the volume control, and overall gain may be adjusted using the 5k preset. The double pole double throw switch, reverses the loudspeaker positions, so that one is used to talk and the other to listen. Manually operating the switch (from inside the house) allows two way communication. Make a PCB in very easy steps. ! Create your PCB design using PCB designer software like Eagle, print out your design on photo paper or glossy paper with laserjet printer. Stick the printed design on the PCB (copper side) and then heat it using hot iron plate. The ink will stick on the PCB and it will be ready for etching process. Note: If you don`t have laserjet printer, then you can print the design on standard paper. Copy the printed design at Copy Service around your location (with glossy paper).

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