Looking to create a multiline, multidigit phone number telephone system/network independent of the current pstn.

Thread Starter

byaeger

Joined May 3, 2020
1
Hello! My name is Bryson, I'm just a hobbyist. I and a few of my neighbors are looking to create a multi-line, multi-digit phone number, phone system using either our existing pstn wiring in our houses or just diy/test wiring. I have all of the tools necessary. I have no clue where to start, I have looked for hours on google and other search engines on how to do this, I have a basic idea on how to make a dtmf decoder, but the dtmf decoder I saw how to do is only single digit using a MT8870. It only has 4 outputs and I saw a video of a guy saying that you could connect these 4 outputs to a microcontroller of some sort and do multi digit phone number capabilities, but he didn't show us how to specifically do that. Hope this isn't too much to ask! I just have a curious brain like all of us! Any feedback is appreciated!
 

Papabravo

Joined Feb 24, 2006
13,931
Hello! My name is Bryson, I'm just a hobbyist. I and a few of my neighbors are looking to create a multi-line, multi-digit phone number, phone system using either our existing pstn wiring in our houses or just diy/test wiring. I have all of the tools necessary. I have no clue where to start, I have looked for hours on google and other search engines on how to do this, I have a basic idea on how to make a dtmf decoder, but the dtmf decoder I saw how to do is only single digit using a MT8870. It only has 4 outputs and I saw a video of a guy saying that you could connect these 4 outputs to a microcontroller of some sort and do multi digit phone number capabilities, but he didn't show us how to specifically do that. Hope this isn't too much to ask! I just have a curious brain like all of us! Any feedback is appreciated!
Unfortunately for you the MT8870 went EOL before the end of the last century. I don't think there is a replacement.
 

ebeowulf17

Joined Aug 12, 2014
3,274
Hello! My name is Bryson, I'm just a hobbyist. I and a few of my neighbors are looking to create a multi-line, multi-digit phone number, phone system using either our existing pstn wiring in our houses or just diy/test wiring. I have all of the tools necessary. I have no clue where to start, I have looked for hours on google and other search engines on how to do this, I have a basic idea on how to make a dtmf decoder, but the dtmf decoder I saw how to do is only single digit using a MT8870. It only has 4 outputs and I saw a video of a guy saying that you could connect these 4 outputs to a microcontroller of some sort and do multi digit phone number capabilities, but he didn't show us how to specifically do that. Hope this isn't too much to ask! I just have a curious brain like all of us! Any feedback is appreciated!
You'll need something to act as a switchboard, joining the lines of any two (or more?) phones that want to connect. So, you'll need a switchboard location that all of your phone lines feed into, and an automated system to recognize off hook status, listen for and interpret a sequence of pulses or dtfm tones, and then activate relays or switches of some sort to make the connections.

This Wikipedia article, especially the section on early automated exchanges, provides a little more detail on the scope of the problem. I think this might be a bigger project than you think! If you really are up for it, it should be an interesting challenge.

https://en.m.wikipedia.org/wiki/Telephone_exchange
 

MisterBill2

Joined Jan 23, 2018
6,331
Bryson, this is an interesting project that is possibly similar to the very early phone systems of a hundred years ago. But with modern technology the system can be much more compact. Certainly it is possible, one option is to copy some system already designed and available on the market, or more likely a system no longer for sale.
But there are a whole lot of questions about requirements before going any farther. How many different phone connections do you want? How much privacy is required? Can a "party line" system be acceptable, or is there a requirement that multiple separate conversations be possible at the same time? A "party-line" system using surplus military phone equipment and a single pair will be by far the simplest and cheapest way to go, But it offers no privacy and as many participants in a single conversation as there are stations.
So you need to provide more detail on the requirements.
 
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