3 Intercom circuit using LM386 – OP-Amp ICs
See Intercom circuit using LM386 and other IC. louder transistor version. And easy and cheap. With Condenser MIC and Speaker, longer cable. Read more
Telephone circuits
Simple Telephone Ring Amplifier circuits
The telephone repeater circuit or The call signal peripheral circuit to the loud than the original,with a buzzer or a electric bell, to increase loud sound Read more
The telephone line status indicator
The telephone line status indicator to prevent the hearing others talk on the phone accidentally and a Protection to making phone calls simultaneously. […] Read more