Simple Door Phone Intercom Circuit Schematic (Duplex)

A door phone intercom system provides a two-way conversation that is cost free. It can be very useful in hospitals, hotels and as a free of cost communication to a friend’s house.Earlier I had already published another two way communication intercom circuit but it had the disadvantage of switching (same speaker is used both as mic and speaker based on the switch positions).

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

                                                                Click on the image for enlarged veiw

Components Required

  1. Condensor mic X 2
  2. Resistors(4.7K,330×2,100k,33k)
  3. Capacitors(.22uF,100uF,220uF,10uF,470pF,470uF)
  4. Zener diode 3.3V
  5. UM66 IC
  6. Push button
  7. Speaker
  8. IC 1895

Working

  • 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….;)

Components Pin out

13 thoughts on “Simple Door Phone Intercom Circuit Schematic (Duplex)

  1. Hi Boss,

    I would like to use this as door phone. So the visitor press the button and will release immediately but I want to talk to him for a while. How is it possible?….Can you pl help me?…What changes do i need to do on this circuit. Will this work for 30 meters range?

    Thanks,
    Shine K P

  2. I appreciate your knowledge on electronics projects. u have learned a lot from here. am doing a final year project which I have designed to turn on/off electrical appliances remotely using DTMF instead of a microcontroller but am facing problems on making the whole thing work. please help me

    • You may use 330 pF or 560 pF, since this capacitor does not seem to be a critical component. I think it is a high cut-off filter in the negative feedback path used to suppress oscillations.

  3. This circuit is theoretically possible but practically impossible! It is not clearly explained exactly how the two speakers and two microphonea are to be placed, that is, the exact layout drawing would have been very much helpful in understanding the practical usage of this circuit.

Leave a Reply

Your email address will not be published. Required fields are marked *