How can I make a 3 way latching circuit that has a master and 3 slaves like a 2 way intercom but instead, the 3 slaves can only communicate with the master one at a time. The master circuit has all the control for the flow of the communication and led indicator to show which slave is ringing. Thanks~

 

Do you just want the units to communicate only with the master and not one to another?
If not, one way is to have a central amplifier, and all intercom units than have the amp output connected via a changeover switch to the intercom speaker. When you operate the switch, the speaker is then connected to the amp input and acts like a mic. All the other intercoms can hear what is being said.
Where I worked years ago had this system and ran a couple of dozen units. It was a 120W valve amp.
Each unit will need shielded cable to stop feedback.
The speakers were connected via transformers to raise the impedance.

Another thing you can do is to use IP phones and run a telephone exchange like FreeSwitch or Asterisk on an old PC or a Raspberry Pi. That is what I have here at home. There is a software addon that allows you to use the phones in the intercom mode too.
I use SPA942 phones and it all runs on the house Ethernet. If you have a Power Over Ethernet network switch, then the phones do not need an extra power supply.

 

I guess I only need the system to communicate through the master only and I found this rather really simple circuit, is there a way to modify this to make it in line rather than being a wireless system? Also is there a way to replace those Transformer drivers in the circuit? Thanks~

 

hi Blind,
Are you asking for a simple 'wired' point to point intercom system.?
E

 

Well, something like this. Also would it be possible for the speaker to also act like a mic? Since I want the slave to consist only of one momentary switch (to dial the master) and 1 speaker while the master consist all the necessary circuits including the controls and amplifier.

 

hi,
A speaker can be used as simple, low quality microphone, but it should have a basic audio amp at the speaker end, that will amplify the speaker 'mike'

How long are the cable runs from master to slaves.?
E

 

hi,
A speaker can be used as simple, low quality microphone, but it should have a basic audio amp at the speaker end, that will amplify the speaker 'mike'

How long are the cable runs from master to slaves.?
E

I guess it would need up to approx. 50 meters.