In this intercom schematic, the 8 ohm speakers is used as microphone and listening speaker. The 10K potentiometer controls volume and the total gain can be set with de 5k R. Use a double switch with 2 ...

There’s a few open source options out there for creating electrical schematics. KiCad and Fritzing are two that will take you from schematic capture to PCB layout. However, there’s been limited ...