08-16-2017, 09:36 PM
intercom using ic lm386 working principle
In this doorphone circuit,an 8 ohm speaker is used both as a microphone and also an output device. The BC109C stage amplifies in common base mode, giving good voltage gain , whilst providing a low impedance input to match the speaker. Self DC bias is used allowing for variations in transistor current gain. An LM386 is used in non-inverting mode as a power amplifier to boost voltage gain and drive the 8 ohm speaker. The 10k potentiometer acts as the volume control, and overall gain may be adjusted using the 5k preset. The double pole double throw switch, reverses the loudspeaker positions, so that one is used to talk and the other to listen. Manually operating the switch (from inside the house) allows two way communication.
The circuit mentioned here is a small easy to build Intercom circuit using one LM386 IC one 2N3904 transistor and few other components. LM386 is a very famous amplifier ICs mostly used by electronics hobbyists in audio circuits. In this circuit the 8 ohms speakers are used for both purposes one as speaker and second as microphone. The 10K variable resistor is used to adjust the volume and 5K variable resistor between the pin 1 and 8 is used to adjust the gain. For switch use DPDT push switches on the both sides. Also include the power on off connection with in the DPDT push switch it will save the battery connected to the circuit all the time and the battery will only connect to the circuit when some one push the switch for talking. Use 9V battery or 9V power supply with the circuit.