The main component used here in this two way intercom circuit is an 1895 IC. It is a 1 watt audio amplifier. Here we are using two condenser mics and two speakers for communication. Calling tone is generated by using melody generator IC UM66.
This door phone intercom system is commonly used for short range applications but can also be extended for long range with the help of audio repeaters. This can be made wireless by connecting fm transmitters and receivers. May be next time we will try to publish one of wireless type.
Here are some of the advantages of these intercom systems for home:
- Low noise communication.
- It is a duplex intercom, so the two persons can talk simultaneously.
Door phone intercom schematic
- Condensor mic X 2
- Zener diode 3.3V
- UM66 IC
- Push button
- IC 1895
- Two condenser mics are connected in parallel which are biased by a resistor R3.
- C2 and C1 are input and output coupling capacitors respectively. They are used to avoid DC shift.
For simplicity, let us divide the whole circuit into 3 parts- Input, Amplifier and Output sections.
- First section consists of mics and the tone generator. Output of tone generator IC UM66 is connected in parallel with the condenser mic for amplification.
- Second is the amplifier section which consists of the amplifier IC 1895.
- Output section consists of two 8 ohm speakers connected in parallel that reduces the total impedance to 4 ohms. So there is an impedance matching between the speaker and amplifier IC. Hence there is maximum power transfer (i.e. maximum efficiency).
So start building one to enjoy free calling to your loved ones….;)