[chbot] DTMF tone frequencies - why?
gb7ipd at gmail.com
Thu Sep 16 01:01:42 BST 2021
That nails it - Thanks Stuart, I'll sleep better tonight knowing what the
original rules were ;)
On Thu, Sep 16, 2021 at 11:41 AM Stuart Brown <stuartbrown2 at gmail.com>
> I found an interesting write up here
> (while waiting for a compile to finish)
> On Thu, 16 Sept 2021 at 10:52, Robin Gilks <gb7ipd at gmail.com> wrote:
>> Greetings all
>> I've used DTMF tones for several projects coding transmitters (usually
>> with sine wave lookup) and receivers (usually with a simple Goertzel
>> decoder) but the actual frequencies I've taken for granted as a part of the
>> spec (ETSI ES 201 235-2).
>> My question is, why these frequencies ? apart from being in the speech
>> band for signalling over telephone wires.
>> Why 697, 770 etc and why not 700, 777 and so on. Looks like the
>> frequencies are 10.5% apart in each of the low and high ranges and they
>> avoid 50, 60 & 400Hz harmonics (from PSUs) as far as I can see.
>> It all looks pretty arbitrary and just happened to be what someone at
>> Bell chose for the original TouchTone system. I'm sure someone in the group
>> could give some historic context to these common beeps we hear in our ears
>> so often !!
>> Robin Gilks
>> Chchrobotics mailing list Chchrobotics at lists.ourshack.com
>> Mail Archives: http://lists.ourshack.com/pipermail/chchrobotics/
>> Meetings usually 3rd Monday each month. See http://kiwibots.org for
>> venue, directions and dates.
>> When replying, please edit your Subject line to reflect new subjects.
> Chchrobotics mailing list Chchrobotics at lists.ourshack.com
> Mail Archives: http://lists.ourshack.com/pipermail/chchrobotics/
> Meetings usually 3rd Monday each month. See http://kiwibots.org for
> venue, directions and dates.
> When replying, please edit your Subject line to reflect new subjects.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Chchrobotics