相关元件pdf下载：lm386 
in this dophone circuit,an 8 ohm speaker is used both as a microphone 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 f variations in transist current gain. an lm386 is used in non-inverting mode as a power amplifier to boost voltage gain drive the 8 ohm speaker. the 10k potentiometer acts as the volume control, 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 the other to listen. manually operating the switch (from inside the house) allows two way communication.
