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DTMF signalling

shermans
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Registered: ‎07-09-2007

DTMF signalling

Does anyone have any knowedge about DTMF signalling ?  I need to pick someone's brains.
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8 REPLIES
VileReynard
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Re: DTMF signalling

shermans
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Re: DTMF signalling

Thanks.  Interesting and helpful but not what I need.  My problem is that I use a DTMF signaller which is causing problems and I hoped I might find someone who knew a bit more about how to create signal tones perhaps on a PC.
VileReynard
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Registered: ‎01-09-2007

Re: DTMF signalling

The two tones appear to be equal amounts of the low tone and the high tone added together (in a linear way).
You might find the attached pdf has more detailed info - USA orientated...

shermans
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Re: DTMF signalling

Again, many thanks.  I have downloaed it but it will take some time trying to digest it ! Undecided
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Registered: ‎11-08-2007

Re: DTMF signalling

About 20 years ago I wrote a simple Linux script on a Sun workstation to extract the telephone number from a networked telephone directory, and then played a series of prerecorded DTMF audio files corresponding to each digit of the phone number through the computers loudspeaker.  By holding a telephone handset next to the speaker, it would work as a simple auto-dialer.
You can easily find prerecorded DTMF audio files on the internet (for example search for "DTMF .wav"), and you should then be able to play the relevant tones to suit your purposes.
shermans
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Registered: ‎07-09-2007

Re: DTMF signalling

purleigh
Thank you so much.  That is exactly what I wanted - perfect.
The signaller is playing up by asking me to acknowledge it first before it will allow me to send the usual signals usung the telephone keypad.  It never did it before and I may not be able to "fudge" it this way, but at least I can try.  The other possibility is that cross-over / noise on the line is setting someone else's signaller off, which is what I am hearing and I hope that I may be able to fool it.  It is a very rural location along way from the exchange, and I am suspicious also that this happens when it is been either very wet or frosty.  If it is cross-over / noise, then there is no point reporting ther fault - I am talking about France and all I will get is the usual "Gallic shrug" because France Telecom still has a monopoly in rural areas.
Thanks again.
Community Veteran
Posts: 5,472
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Registered: ‎11-08-2007

Re: DTMF signalling

Did you notice within the link in Reply #1, that additional signaling special tone frequencies used in Europe may be different from those used in the UK, so that might be where you are having a compatibility problem - if you are trying to use UK tone generator on the French network.
Using the computer to play audio files, you should be able to find the European alternative tones, and see whether that fixes your problem.
shermans
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Re: DTMF signalling

Thanks, but there never has been a problem during the last ten years until recently and it has got steadily worse.  Basically, I have a DTMF tele-switch to turn the boiler on and off before and after letting.  Normally, you dialled the house from the UK, wait until it answered, entered a four digit code which was then acknowledged, and entered 1 or 0 to switch between on and off.  During the last year, I get a DTMF tone (like a fax polling) which interupts as soon as the phone is answered, even when the signaller is isolated by plugging it directly into the master telephone socket.  There can therefore be no other equipment in the house which can be causing this.  It must either be a fault with the teleswitch or, as I suspect, external interference.  It has got worse over time.  In the recent past, I would manage to get through without being interupted by the polling after several attempts, but now it is permanent.  When one of the guests called me on the telephone recently from the house, I also heard the polling, which does suggest that it is cross-over from someone else and not my signaller.  So I thought that I might be able to send an "Acknowledge" DTMF tone to see if I could stop it and then go from there.
If I have no luck, then I intend to disconnect the signaller and bring it back to the UK to try it here, which would prove whether it was cross-over or a fault with the unit.  Trying to replace it would be difficult and expensive these days because it is old technology, but it has always been to easy to use in the past.