Circuit Schematic Diagram Door Phone Intercom




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. 



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