I 've started a project to put a Adafruit FONA Feather inside my old Western Electric Model 2500...

[G+_Chad Lawson]

I've started a project to put a Adafruit FONA Feather inside my old Western Electric Model 2500 phone.

 

At this point, I've managed to get the handset working and I have a plan for the ringer.

 

What I'm trying to do now is interface with the original keypad. It's a standard 35 type pad (3x4) and I have various schematics for the whole phone system, but I'm not quite getting my head around which of the eight wires power it and which one(s) to use to listen to the tones.

 

I have a couple DTMF ICs and a breakout board somewhere, but finding the right wires is my stopping block and I don't have the knowledge/tools to diagnose this on my own. And I don't know the right terms at this point for a deeper search.

 

I'm betting that there is a couple old-school telephony folks on here that can help.

 

Here's some of what I've found:

 

http://www.repeater-builder.com/tech-info/dtmf/bell-dtmf.html

http://www.angelaitp.com/2017/03/20/spring-break-updates/

 

The easy ditch would be to just use a more updated, all-digital keypad, but I'm trying to use as much of the original components as I can.

[G+_Paul Hutchinson]

I would remove all the electronics from the keypad assembly and open it up enough to make direct connections to the switches. It probably requires extensive mechanical and electrical modification but in the end should end up looking like the original.

[G+_Black Merc]

Paul Hutchinson don't open the switches! Those key pads were matrix connected (3x4 if I recall). A micro controller made the dual tones per key pressed... Each wire had a different signal associated with it.. #1,4,7 had a signal based on that wire connection, #7,8,9 had a signal based on that wire connection. Now, those two signals together create a tone that represents #7. Sent across the phone connection the Telco system knows what number you want.. The same is also used in ham radio...

[G+_Paul Hutchinson]

Black Merc No micro's or even IC's in 60's consumer tech, take a look at the schematic in the one of the OP's links.

 

IMO, when interfacing to an Adafruit micro-controller system, or any modern micro, it is not of any value to keep the DTMF capability vs. just hooking up to the raw 3x4 matrix of switches.