Wiring And Schematic

This is an intercom schema which use LM380 as the audio amplifier and 2 transistors as the microphone pre amplifier. The sound quality will be good enough with low cost building.

This schema consists of two identical intercom units. Each unit contains a power supply, microphone preamplifier, audio amplifier and a Push To Talk (PTT) relay schema. Only 2 wires are required to connect the units together. Due to the low output impedance of the mic preamp, screened cable is not necessary and ordinary 2 core speaker cable, or bell wire may be used.

Detail explanation about this intercom schema include the PCB layout, please visit this page

This is a 2-station simple intercom schema build based on transistors part and using common 8R mini speakers. The speaker works as microphone and generate sound, so there is no need microphone for this intercom. The "press-to-talk" switches should have a spring-return so the intercom can never be left ON, push on switch can be used for this kind of task.



The secret to preventing instability (motor-boating) with a high gain schema like this is to power the speaker from a separate power supply! You can connect an extra station (or two extra stations) to this schema design.

Build the schema into two separated boxes (for 2 stations). On each box should be use 2 ports for external power supply port (if you use external power supply, not battery) and connection port to other stations. Create some holes for speaker push on switch.