Date   : Mon, 30 Apr 2007 23:30:45 +0100
From   : andrew.chesterton@... (Andrew Chesterton)
Subject: Tone Dialling Frequencies

> -----Original Message-----
> From: 
> bbc-micro-bounces+andrew.chesterton=ntlworld.com@...
> co.uk 
> [mailto:bbc-micro-bounces+andrew.chesterton=ntlworld.com at lists
> .cloud9.co.uk] On Behalf Of Ian Wolstenholme
> Sent: 30 April 2007 21:54
> To: bbc-micro@...
> Subject: [BBC-Micro] Tone Dialling Frequencies
> 
> 
> I'm sure this should be possible, but I can't get
> it to work - can the BBC sound chip generate
> the frequencies used for tone dialling on telephones?

I'm not sure if the BBC sound chip can output 2 different frequencies
simultaniously.
Tone dialing uses a system called Dual Tone Multi-Frequency or D.T.M.F.
where a pair of frequencies are generated for each digit required. I
can't remember the exact pairings used, but a quick Google should
provide the answers.

> 
> I've got the list of frequencies for the numbers
> and the sound chip data sheet but I can't get any
> output which sounds like the right notes.  I think
> I may be going wrong somewhere with the divide
> by 4000000 bit.
> 
> Can anyone point me in the right direction, or even
> write a bit of code to do it?
> 
> The dial on the BeebMaster GPO telephone gave up
> a few years ago and since then I've been using a
> little tone generator number pad thing but it's finally
> given up as well so I either get wrong numbers or
> that lady telling me I've mis-dialled!  I thought it
> would be good if I could get one of my Beebs to
> do it!
> 
The basic DTMF generator chips are fairly cheap and don't require many
external components if you fancied doing some hardware as well. It's
quite a few years ago that I played with a design for voice dialing
phones for the blind!

> Best wishes,
> 
> 
> 
> Ian
> 
> 

Hope this helps,

Andrew.