Dtmfout

PHM102

Hi i am doing a project using the DTMFOUT. We followed the circuit shown on the manual however it did not work. We can hear that pluse tones is generated in the background but the circuit does not call. (As in the calling party phone did not ring) Is there any guidelines whereby we can follow to troubleshoot?

DTMFOUT 0, 500, 100, [noparse][[/noparse]9, 3, 3, 8, 2, 5, 9, 9] 'Our country uses 8 digits

P.S: We did not connect the sidactor as we were told that it was not needed (Unless there is a power surge)

Thanks in advance

Regards,
Gavin

Chris Savage

Gavin,
·
·· It may be a matter of the level of the sound coming from the interface.· Perhaps it is not loud enough for your local phone company switch to ‘hear’ the tones properly.· You may need a better connection or need to revise your current one.

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Chris Savage
Parallax Tech Support

PHM102

Hi instead of using the 600 - 600 Ohms transformer we are using the 3K - 3K ohms transformer. Is this possible as we could not get the 600 - 600.

PHM102

Chris Savage (Parallax) said...
Gavin,

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com[noparse]:office:[/noparse]office" /><o> </o>

<SPAN style="mso-spacerun: yes"> It may be a matter of the level of the sound coming from the interface.<SPAN style="mso-spacerun: yes"> Perhaps it is not loud enough for your local phone company switch to ‘hear’ the tones properly.<SPAN style="mso-spacerun: yes"> You may need a better connection or need to revise your current one.

Thanks for the speedy reply, could you explain what do you mean by the level of sound coming from the interface? (If possible could you provide us with some examples) Pardon us for our ignorance as we are still new in this area.

Regards,
Gavin

PJAllen

The 3k:3k that you are using is likely resulting in an impedance mismatch.· What it boils down to is that your tones aren't loud·enough to register with your Central Office [noparse][[/noparse]CO].·

As an alternative, perhaps you might consider connecting the Stamp-DTMF output to an audio amplifier and holding a speaker to the handset (like an old acoustic coupler.)

** Post Edit **· Back in the Bad Old Days, in the era of pay phones, there were little hand-helds which you'd hold to the phone that used just this approach.· On a similar note (haha) you might be able to amplify the Stamp-DTMF output to compensate for the mismatch (by brute force, so to say.)


Post Edited (PJ Allen) : 11/5/2006 5:09:59 PM GMT

PHM102

Thanks for the reply i will look into in

PHM102

I just managed to get a 600 - 600ohms transformer and tried out the circuit but it fails to work. When the phone line is plug into the circuit, we could hear echos on the another phone of mine. The dialing tones are very soft and is almost impossible to hear. Anyone know what is the problem? Or we have to connect it to an audio amplifier such that it can register with the CO?

DaveG

Gavin,

You might try reducing the series 1K resistor to 220 ohms.

Dave G

Chris Savage

Which Stamp Model are you using?

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Chris Savage
Parallax Tech Support