If you are looking for a simple and low cost intercom system for home installation, you would love the explained project.
The circuit only uses a single chip for the amplification purpose and a couple of speakers along with a handful of passive components for acquiring the intending intercom application circuit.
As seen in the figure the entire circuit hovers around the IC LM380 which is another versatile amplifier IC just like it's younger brother IC LM386.
The IC is manufactured by:
However this chip is even better as it requires very few external components for implementing the amplifier actions.
In the diagram we see that the input of the IC is connected to a small loudspeaker via a small output transformer.
The output of the IC is also connected to a loudspeaker.
A DPDT switch is configured and connected to the two speakers such that the whole circuit works like a two way intercom system.
The connected loudspeakers act as a speech producing devices as well as mics for capturing sound signals for amplification to the other end.
The right end speaker is the master while the speaker connected at the other end is for remote installation.
When the switch is positioned toward the talk mode, the master speaker behaves as the mic, and the sound signal is announced and heard over the remote speaker.
When the switch is positioned toward the listen mode, all the conservation that might take place around the remote speaker is transferred and can be heard over the master speaker.
T1 is nothing but a small audio output transformer which may be easily procured from the market, the winding with lower impedance goes to the speaker while the side with the higher impedance gets connected to the input of the IC.