This intercom circuit based on IC LM380 audio amplifier requires very few external components. So the circuit is very easy to assemble.
Circuit diagram of the intercom is shown in Fig. 1. In addition to audio amplifier LM380 (IC1), it uses a condenser microphone (MIC1), an 8-ohm, 0.5W speaker and a few other components.
Fig. 1: Circuit diagram of super-simple intercom
Assemble the same circuit on two separate units. In order to use these units as intercom, extend the output (LS1) of the first unit to the second unit placed in a remote location and vice versa. Set the required sound level by adjusting potmeter VR1. Press switch S2 momentarily to generate an audio tone in the speaker (LS1).
The circuit works off a 9V DC battery. Alternatively, you can also use a 9V unregulated power supply.
Construction and testing
A PCB layout for the intercom is shown in Fig. 2 and its components layout in Fig. 3.
PCB layout for the intercom
Components layout for the PCB
Download PCB and component layout PDFs: click here
To test the circuit, you need two units of the same circuit. Extend LS1 from the first unit to the second unit, and LS2 (not shown here) from the second unit to the first unit.
To talk over the intercom, press switch S2 to ring up the person sitting on the remote side where the second unit is placed. Then you can speak into microphone MIC1. The person at the other end should be able to hear you through LS1. Similarly, when he rings you up, you should be able to hear him through LS2.
Use shielded wires for connections to both the units.