Where are the DTMF tones generated in a WE 2500 phone?

[MaximRecoil]

I was looking at the keypad assembly on my WE 2500 (made in the early '80s), and there doesn't seem to be a mechanism within the keypad assembly itself for generating tones; all I saw in there was a series of leaf switches, springs, and associated mechanical devices for activating the right leaf switches when a number key is pressed. Does that mean that the tones are generated in the network? I noticed that its network looked different than the typical 425B or 425E network in a rotary WE 500.

[Phonesrfun]

They are, indeed, generated in the dial.  There are two tuned circuits, one for each of the high and low tones.  It is done with a single transistor which oscillates at two frequencies simultaneously.  The tuned circuits each have coils that have multiple taps which are switched in by all those leaf switches.

There is no functional difference between a 425B and a 425E network.  Only the addition of a couple terminals to facilitate connecting the dial.

[MaximRecoil]

Thanks for the information. I've been trying to figure out a way to use the internals of a WE 2500 in an old Intellicall 3003 payphone to make it into a coinless phone, but I guess the only way to do it would be to get one of the "dumb" metal payphone keypads that are designed to simply cover a plastic keypad and push its keys when the metal keys are pressed; and fabricate some sort of a mount for it.

What about the newer copies of 2500 phones made by e.g. Cortelco, Avaya, Premier, etc.? I believe those simply use a circuit board beneath the keypad (like a typical modern remote control or gamepad), doing away with the complex leaf switch arrangement (my Intellicall payphone keypad is like this; i.e., just a circuit board beneath the keys that doesn't seem to have any components on it). Do those also generate the tones right on the circuit board or do they do it elsewhere?

[Phonesrfun]

All touchtone keypads generate the tones all by themselves.  The more recent ones use an IC chip made just for that purpose,  The keypad itself is just the matrix that tells the chip which key was pressed, and the chip responds accordingly with the proper two tones.

[MaximRecoil]

The IC that generates the tones in my Intellicall keypad must be surface mount then, because there's no sign of an IC or any other component on the side of the PCB that's visible; there is just an electronic ringer, a 20-pin connector, and several terminals:



Since it generates its own tones, does that mean it could be wired to the network of a 2500 phone (provided the pinout could be figured out) and work properly?

[dpaynter1066]

That used to be the case,  With the introduction of telephones on a chip, the keypads on some newer phones (and pay phones) are just a switch matrix now.

For instance, the  U3761MB Universal Telephone IC integrates all functions necessary to build a standard telephone circuit: speech circuit, dialer with re-dial, notice function (save), ten two-touch as well as three one-touch memories, and tone ringer.  This chip was introduced in 1997.

Others use a dedicated dialer chip to decode the keypad matrix into touch tones and use external networks.

Payphones.com sells a board that does what you want.
http://www.payphone.com/Armored-Phone-Circuit-Board.html

Or why not just call Intellicall and ask them about it?

[HarrySmith]

There is an instruction sheet about wiring a touch tone keypad to any old phone. It was written by a long time member of one of the phone clubs. The strange thing, I thought, was only 2 wires are used! I have it saved somewhere at home, I will try to find it and post it here.

[MaximRecoil]

That used to be the case,  With the introduction of telephones on a chip, the keypads on some newer phones (and pay phones) are just a switch matrix now.

For instance, the  U3761MB Universal Telephone IC integrates all functions necessary to build a standard telephone circuit: speech circuit, dialer with re-dial, notice function (save), ten two-touch as well as three one-touch memories, and tone ringer.  This chip was introduced in 1997.

Others use a dedicated dialer chip to decode the keypad matrix into touch tones and use external networks.

Thanks for the information. Very interesting.

Payphones.com sells a board that does what you want.
http://www.payphone.com/Armored-Phone-Circuit-Board.html

Yes, but it isn't compatible with my keypad. It uses a 7-pin keypad connector, and my keypad has a 20-pin connector. Also, if possible, I'd like to use Western Electric internals. I know that the 2500 is a good phone from experience, and I know nothing about the quality of that expensive little PCB from payphone.com that was probably made in China.

Or why not just call Intellicall and ask them about it?

I've tried a few times over the past few days and no one answers the phone.

There is an instruction sheet about wiring a touch tone keypad to any old phone. It was written by a long time member of one of the phone clubs. The strange thing, I thought, was only 2 wires are used! I have it saved somewhere at home, I will try to find it and post it here.

That would be great.

[HarrySmith]

Found it!


I did not realize it is 44 pages! It is also in an old word format. I do not know if the attachment will work for everyone. If you are interested and cannot get it, let me know and I can email it to you.

[Jester]

To Harry et. al.

I ran across this info. on the ATCA website years ago & posted a link in another thread. If you have trouble opening Harry's attachment (which I didn't), try the link;
http://atcaonline.com/ttpad.html

[MaximRecoil]

Thanks for the document. It is a good thing to know how to do that. Unfortunately it won't help with what I want to do, because I'm pretty sure my Intellicall keypad is just a switch matrix, as mentioned by dpaynter1066.

As far as I can tell, I only have two options for making that payphone work as a coinless phone the way I want it to:

1. Buy a "dummy" metal keypad (link) which is designed to have a plastic keypad mounted directly behind it, and fabricate some sort of a mount for it and a 2500 keypad behind it. Then I could easily use the rest of the 2500's internals.

Or:

2. Buy a payphone-type keypad with a 7-pin connector that is compatible with the coinless circuit board that payphone.com sells (like this one - [link] which would mount right up to my payphone as-is), and of course, buy their coinless circuit board as well. The problem with that is: it would be about $100 for those two items, and I'd be stuck with a proprietary little circuit board of unknown quality for a phone. Will it give good quality calls? Will it stand the test of time? If/when it goes bad, will "payphone.com" even still be around? On the other hand, I know I can find 2500 internals indefinitely.

[HarrySmith]

I recall seeing a lot of 5 or 6 payphone keypads listed on eBay, they do not sell and are consistently relisted. The seller also lists & relists other lots of payphone parts. I do not recall the seller and did not search today but they are always there when I do my phone searches. They were not expensice IIRC.

[MaximRecoil]

I recall seeing a lot of 5 or 6 payphone keypads listed on eBay, they do not sell and are consistently relisted. The seller also lists & relists other lots of payphone parts. I do not recall the seller and did not search today but they are always there when I do my phone searches. They were not expensice IIRC.

You mean these - link? I wonder if one of those could be wired up to 2500 internals? Do you (or does anyone else) know if it could? The mounting bracket for them is the same as on my Intellicall; i.e., drop-in fit.

I wish they were being sold individually ... I don't need 4 of them. The seller says he/she has a bunch of them, so maybe I'll send a message and see if he/she will sell just one.

[HarrySmith]

Those are the ones. Yes, they always say they have a bunch of whatever parts they have listed, must have gotten ahold of a bunch of dismantled payphone stuff. I would think they would sell one, can't hurt to ask. As far as wiring, I am not familiar with them. The guy who wrote that piece on wiring a keypad to a rotary phone, Stan Schrier and Mike Davis from the lists are the experts on that stuff. I do not think they are here but you can find them on the lists.