门禁电话通话电路图
In this dophone circuit,an 8 ohm speaker is used both as a mrophone and also an output device. The BC109C stage amplifies in common base mode, giving good voltage gn , whilst providing a low impnce input to match the speaker. Self bias is used allowing for variaons in transistor current gain. An LM386 is used in non-inverting mode as a power amplifier to boost voltage gain and drive the 8 ohm speaker. The 10k pontiometer ts as the volume control, and overall gain may be justed using the 5k preset. The double pole double throw switch, reverses the loueaker 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.