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.