Designing a pulse-to-tone converter - UK Vintage Radio Repair and Restoration Discussion Forum

xantaus · 13th Nov 2010, 3:49 pm

Is there a set of instructions around for making your own pulse to tone converter? For the cost of the one linked (and maybe a little more expensive) I'd enjoy creating one myself.

Thank you everyone for your help so far, this whole affair has been most enlightening.

twocvbloke · 13th Nov 2010, 4:04 pm

I think the electronics of one of them converters is probably simple to put together, but I think the price they ask isn't too much, you can get one for as little as £24 like this one on ebay:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=190466576672

Just wire into the phone and off you go...

xantaus · 13th Nov 2010, 4:43 pm

Quote:

Originally Posted by twocvbloke

...I think the price they ask isn't too much

It's not the price, I nearly always prefer doing things for myself when the quality of my work is good, and the cost isn't vastly higher.

I've just quickly done some reading on dual tone multi frequency dialing, which I believe is the modern standard.

I see the converting process as thus:

count the number of pulses (cut off delay equal to slightly longer than the time between pulses on a normal dial)

This number refers to 2 separate tones, both of them must be played simultaneously. Tones must be 70ms long (is there a maximum duration?).

twocvbloke · 13th Nov 2010, 4:57 pm

I know what you mean, nothing more satisfying than seeing your own work in action, but, I just think that to make something like the rotatone, it needs more than a dab hand with a soldering iron, as it probably involves programming a microchip which senses the pulses and turns them into tones, aswell as the extra features it has, such as adding a * and # function, memory functions, I think the cost if you were to make a single one yourself (factoring in buying the tools, the programmer, the parts (usually needing to be bought in bulk)) would be more than to buy a pre-made one...

xantaus · 13th Nov 2010, 5:20 pm

I was curious as to how the extra functions worked (how do you dial a * or # if your 'phone doesn't have a way of signaling them?), but other than that I had no desire for them.

Edit: Just looked up the extra functions which involve holding the dial at the number you desire and then releasing.

Parts are annoying to acquire but I'm not sure what tools I would need? You can connect if up to a speaker and use audio software to check the tones.

While I've never worked on IC chips before I've done a lot of programming so I'm not worried on that front.

If it does turn out to be vastly more expensive to do it myself then of course I'll just buy the pre-made version.

Dave Moll · 13th Nov 2010, 5:48 pm

The way it operates is rather sneaky. Because the unit sits between the dial and the rest of the telephone, it is able to utilise both the pulsing contacts and the "dial-off-normal" switch.

If you rotate the dial and hold it (so that the DON switch is activated but no pulses are sent), the Rotatone cycles through its extended-function modes, such as "*"/"#", memory etc - indicating which mode it is in by one or more bleeps audible in the handset.

twocvbloke · 13th Nov 2010, 8:08 pm

Clever device, that's for sure...

I'm guessing that the Rotatone is only really suitable for mechanical telephones, rather than slightly more modern push-button phones that haven't got the physical switches to intercept?

terrykc · 17th Nov 2010, 7:37 pm

You'll probably need to slug the pulses to avoid errors due to contact bounce etc., but something like this would work:

Detect off-hook to start, then count pulses using a decade counter connected to a BCD decoder with the latter held in an inactive state (all outputs off).

Set a retriggerable monostable (~600mS) to detect the inter-digit gap (800mS). When the mono times out, use it to trigger another mono (100mS) to generate an enable pulse for the BCD encoder. The output of this will need further decoding using gates to generate the row and column signals of a numeric keypad. These, in turn, feed a DTMF generator chip to produce the tones.

It might be possible to simplify some of that but I've described the basic building blocks you'll need.

A question: why do you need such a device? I thought that even modern exchanges still accept LD phones?

julie_m · 17th Nov 2010, 11:33 pm

There's no point using anything but a microcontroller to do the job. Debouncing can be done in software. All the tone frequencies you need can be got by dividing down a 3.579MHz NTSC colour carrier crystal; so use this (better, 2* or even 4* this if you can get) as the µC clock, and generate your audio tones with a simple timing loop controlling two I/O pins.

terrykc · 17th Nov 2010, 11:55 pm

The original request was for "a set of instructions".

The microcontroller solution will obviously work but perhaps xantaus might prefer a hardware solution?

"I'd enjoy creating one myself ..."

At the end of the day, it comes down to what xantaus 'enjoys' best.

On the other hand, I'm the 'new kid on the block' so, perhaps, you already know the answer to that!

13th Nov 2010, 3:49 pm	#1
xantaus Retired Dormant Member Join Date: Sep 2010 Location: Northumberland Posts: 11	Designing a pulse-to-tone converter Is there a set of instructions around for making your own pulse to tone converter? For the cost of the one linked (and maybe a little more expensive) I'd enjoy creating one myself. Thank you everyone for your help so far, this whole affair has been most enlightening.

13th Nov 2010, 4:04 pm	#2
twocvbloke Retired Dormant Member Join Date: Oct 2010 Location: Colne, Lancashire, UK. Posts: 527	Re: GPO 706L not dialing out. I think the electronics of one of them converters is probably simple to put together, but I think the price they ask isn't too much, you can get one for as little as £24 like this one on ebay: http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=190466576672 Just wire into the phone and off you go...

13th Nov 2010, 4:57 pm	#4
twocvbloke Retired Dormant Member Join Date: Oct 2010 Location: Colne, Lancashire, UK. Posts: 527	Re: GPO 706L not dialing out. I know what you mean, nothing more satisfying than seeing your own work in action, but, I just think that to make something like the rotatone, it needs more than a dab hand with a soldering iron, as it probably involves programming a microchip which senses the pulses and turns them into tones, aswell as the extra features it has, such as adding a * and # function, memory functions, I think the cost if you were to make a single one yourself (factoring in buying the tools, the programmer, the parts (usually needing to be bought in bulk)) would be more than to buy a pre-made one...

13th Nov 2010, 5:20 pm	#5
xantaus Retired Dormant Member Join Date: Sep 2010 Location: Northumberland Posts: 11	Re: GPO 706L not dialing out. I was curious as to how the extra functions worked (how do you dial a * or # if your 'phone doesn't have a way of signaling them?), but other than that I had no desire for them. Edit: Just looked up the extra functions which involve holding the dial at the number you desire and then releasing. Parts are annoying to acquire but I'm not sure what tools I would need? You can connect if up to a speaker and use audio software to check the tones. While I've never worked on IC chips before I've done a lot of programming so I'm not worried on that front. If it does turn out to be vastly more expensive to do it myself then of course I'll just buy the pre-made version.

13th Nov 2010, 5:48 pm	#6
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: Designing a pulse-to-tone converter The way it operates is rather sneaky. Because the unit sits between the dial and the rest of the telephone, it is able to utilise both the pulsing contacts and the "dial-off-normal" switch. If you rotate the dial and hold it (so that the DON switch is activated but no pulses are sent), the Rotatone cycles through its extended-function modes, such as ""/"#", memory etc - indicating which mode it is in by one or more bleeps audible in the handset. __________________ Mending is better than Ending (cf Brave New World* by Aldous Huxley)

13th Nov 2010, 8:08 pm	#7
twocvbloke Retired Dormant Member Join Date: Oct 2010 Location: Colne, Lancashire, UK. Posts: 527	Re: Designing a pulse-to-tone converter Clever device, that's for sure... I'm guessing that the Rotatone is only really suitable for mechanical telephones, rather than slightly more modern push-button phones that haven't got the physical switches to intercept?

17th Nov 2010, 7:37 pm	#8
terrykc Rest in Peace Join Date: Nov 2010 Location: North Hykeham, Lincolnshire, UK. Posts: 515	Re: Designing a pulse-to-tone converter You'll probably need to slug the pulses to avoid errors due to contact bounce etc., but something like this would work: Detect off-hook to start, then count pulses using a decade counter connected to a BCD decoder with the latter held in an inactive state (all outputs off). Set a retriggerable monostable (~600mS) to detect the inter-digit gap (800mS). When the mono times out, use it to trigger another mono (100mS) to generate an enable pulse for the BCD encoder. The output of this will need further decoding using gates to generate the row and column signals of a numeric keypad. These, in turn, feed a DTMF generator chip to produce the tones. It might be possible to simplify some of that but I've described the basic building blocks you'll need. A question: why do you need such a device? I thought that even modern exchanges still accept LD phones?

17th Nov 2010, 11:33 pm	#9
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Designing a pulse-to-tone converter There's no point using anything but a microcontroller to do the job. Debouncing can be done in software. All the tone frequencies you need can be got by dividing down a 3.579MHz NTSC colour carrier crystal; so use this (better, 2* or even 4* this if you can get) as the µC clock, and generate your audio tones with a simple timing loop controlling two I/O pins. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

17th Nov 2010, 11:55 pm	#10
terrykc Rest in Peace Join Date: Nov 2010 Location: North Hykeham, Lincolnshire, UK. Posts: 515	Re: Designing a pulse-to-tone converter The original request was for "a set of instructions". The microcontroller solution will obviously work but perhaps xantaus might prefer a hardware solution? "I'd enjoy creating one myself ..." At the end of the day, it comes down to what xantaus 'enjoys' best. On the other hand, I'm the 'new kid on the block' so, perhaps, you already know the answer to that!