Simple intercom circuit for old analog phones

[^rooker]

This is just a quick rip-off (so I don't lose this information) from a [url="https://www.epanorama.net/documents/tel ... ercom.html]document at "ePanorama.net": "Use old phones as an intercom (Markus Wandel, 1990s)"[/url]


Very simple intercom circuit

Get two phone jacks and a 680 ohm, 1/2 W resistor. Connect the components to make the circuit below:

Code: Select all

reen              680 1/2W    +   12V    -          Red
--------------------/\/\/\------|'|'|'|'-----------------
To Phone                                          To Phone
_________________________________________________________
Red                                                  Green

With ability to "call" the other side:

Code: Select all

                              +  | | -
      +-------+------ - - --+---||||---/\/\/--+---- - -----+-------+
      |       |             |    | |     R    |            |       |
      |       |             | 24V             |            |       |
      |      ---            |                 |           ---      |
      |     |   |           +---||------------+          |   |     |
      |      --- Sonalert       C                Sonalert ---      |
      |   C   |                                            |   C   |
      +---||--+                                            +--||---+
      |      _|_,                                         _|_      |
      |      / \  15V                               15V   \ /      |
    PHONE    -+- Zener                             Zener `-+-    PHONE
      |       |                                            |       |
      |       |                                            |       |
      +-------+------------------ - - - -------------------+-------+

Source: https://www.epanorama.net/documents/tel ... ercom.html