Intercom System

Discussion in 'The Projects Forum' started by urb-nurd, Jul 11, 2015.

  1. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    A friend has asked me to hook up an intercom system for him.

    I was wondering if i could save a little time and see if anyone could suggest a method to implement this?

    Here is the specs

    remote room monitor


    Device must contain a loudspeaker with a microphone alongside switches to disable and control gain (gain control does not have to be exposed to user).
    If the loudspeaker is enabled, the loudspeaker should amplify and also output audio signal from receive circuit on telephone connection.
    If the microphone is enabled, the microphone should output an audio signal strong enough to traverse a distance of ~20m without excessive distortion on transmit circuit on telephone connection.


    Device shows volume level of received audio signal even when loudspeaker disabled

    I know a fair bit about microcontrollers and could approach the situation from that stantpoint, but i wondered if there are already pre-existing IC's that i could slap together.

    Any help is greatly appreciated!
  2. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    Just been reading a few instructables and i see a-lot about modifying telephones for this purpose.

    I can deal with the mic and speaker amplification with controllable gain, and i can make a circuit for volume level display easy enough.

    I just lack knowledge on telephone lines. Is it as simple as hooking up the wires from the connector to the circuit?

    I will research more when i get home, i feel this is pretty rudimentary stuff that is throwing me off as i am a youngster of the digital age haha i hardly remember old telephones

    EDIT: just browsing on my phone, is this as simple as taking audio in and audio out from the connectors and simply amplifying and conditioning appropriately?
    Last edited: Jul 11, 2015
  3. ian field

    Distinguished Member

    Oct 27, 2012

    There's an intercom circuit here:

    You can build from scratch as shown in the manual, or you can buy a ready assembled audio amplifier module and add the changeover switching and speakers. Or for less assembly work than the EE circuit - you could build your own audio module with one of the many audio chips that are available.

    The one in the Philips kit uses the speakers to double as the microphone, the amplifier uses a common base input stage for its low input impedance to match better to the speaker. This is a neat trick that you could add on to any of the other options.