Looking for DTMF generator dedicated IC

Thread Starter

rhaggart1

Joined Apr 25, 2020
13
Hi all,

I'm currently reworking an old touch-tone telephone, which involves redesigning the circuit to avoid the whole telephone line high voltage AC circuitry etc.

In my first prototype I got on fine using an IK semiconductor 91214b IC to do DTMF generation, with the keypad keys connected as inputs and the output connected to the handset speaker. However, it's relatively difficult to obtain
There will be a central microcontroller (likely an Arduino Nano or Pi Zero) and I could theoretically just use this for DTMF, but it would involve using up a bunch of I/O which I'd rather not!

Ideally, I'd like to have the DTMF generation on a separate chip, but I'd also like it to be surface mount so I can hide it away on the 'keypad' side of the circuit board and save the other side for everything else that will be eventually packed in.
However, I'm really struggling to find anything suitable, it seems they're mostly not manufactured anymore. There are plenty of decoders, but looking through RS/Farnell/Digikey etc I can't find any generators.

The only generators I've found have to be interfaced with an MCU (e.g. MT8888CS1), and I'm happy enough using something like this (it might even provide even more flexibility). But I don't know how I'd interface my 10 number keys with it, without using whatever my central microcontroller ends up being, so if anyone has any insight here that would also be appreciated!

Thankyou!
 

Thread Starter

rhaggart1

Joined Apr 25, 2020
13
Have you looked into this DTMF generator chip?
https://www.ti.com.cn/cn/lit/an/bpra068/bpra068.pdf?ts=1676962367890&ref_url=https%3A%2F%2Fwww.google.com%2F

Also, what gives you the impression that you would need a lot of I/O to generate tones with an Arduino or similar? It seems one digital output would be enough.
ah sorry maybe I wasn't clear - I would need an input for each row and column so 7 inputs total (4r, 3c)

and thankyou for that link - it definitely sounds like what I'm after so I'll have a more detailed read through it when I find some time today!
 

DickCappels

Joined Aug 21, 2008
10,246
I feel certain that if you look around you can find a DTMF algorithm that can be used to write code to generate DTMF with a AVR controller (or other of your choice). One output pin and probably some input interface - in otherwise, make your own DTMF generator is you don't mind spending time and energy necessary to carry the project through.
 

Thread Starter

rhaggart1

Joined Apr 25, 2020
13
I feel certain that if you look around you can find a DTMF algorithm that can be used to write code to generate DTMF with a AVR controller (or other of your choice). One output pin and probably some input interface - in otherwise, make your own DTMF generator is you don't mind spending time and energy necessary to carry the project through.
I think I've decided to try and use some shift registers to interface with the central controller to reduce the number of inputs required. I think it provides best flexibility and easily obtainable components
 

RPLaJeunesse

Joined Jul 29, 2018
255
If you can accept a DIP part the TP5089N (aka LM5089 and likely originally the MK5089) is readily available as NOS from multiple sources on eBay. Keypad in, proper DTMF out, 3.5-10V supply, 3.579545 MHz crystal controlled. Has muting output to kill the microphone when outputting DTMF. Note that this part requires the keypad to pull the selected row and column down to Vss, it has built-in pullups on these 8 active-low inputs. Also makes it possible to use an 8-line uC port to activate it. A full telephone schematic is in the MM5395N datasheet, a very similar part that only requires SPST keypad switches. Also available on eBay.
 
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