Circuit Schematic Diagram Door Phone Intercom

This schematic shows a doorphone circuit diagram

- 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.

- Self DC bias is used allowing for variations 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.

- 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.

- The 10k potentiometer acts as the volume control, and overall gain may be adjusted using the 5k preset.