DTMF and PIC 16F628A

[ultramegaok]

Hi ultramegaok

I have done a lot of development accessing the PSTN using Pics and PBP Pro
First of all, the DTMF tones out of a PIC are dreadful as produced on the pin - you need to clean them up with an active low pass filter. This will remove all t he nasty higher order stuff that clogs it and will produce a pretty good DTMF waveform. Using a single opamp 2nd order filter, I was able to shape and send tones without problems, and have them accepted at destination. And yes, clock at 20Mhz minimum to make the waveforms acceptable

Eish! (as we say in South Africa before the World Cup). You need an audio transformer and what is called an "active Gyrator" with a single transistor to match to a PSTN line. Will gladly send design tips

You want to receive DTMF with a PIC? Good luck. It's vastly more complicated, so rather use an industry standard IC like the MT8870 decoder IC. The Microchip website has an application note that decodes DTMF, but it looks like complicated software

Will gladly send u the details on the low pass filter if that interests you.

regards

Angus Anderson
KwaZulu Natal, South Africa

Thanks for the information Angus, could you share the low pass filter circuit that you use before...my project is only to send DTMF (just Dialing)

my email is [email protected].


Greeting from Mexico!!!!

I think my futbol team is going to be in the inaugural game against your team in the wolrd cup

[abdulmueed]

Thanks for the information Angus, could you share the low pass filter circuit that you use before...my project is only to send DTMF (just Dialing)

my email is [email protected].


Greeting from Mexico!!!!

I think my futbol team is going to be in the inaugural game against your team in the wolrd cup

please if you got the solution please tell me too i am also stuck.. i also have to generate DTMF dail tone to call through phone line using pic.. i am using pic 16f877a with 20mhz crystal.. in my programmer i have dtmfout instruction.. i can write dtmfout porta.0, [3] and it will generate dtmf for numbe 3 at porta.0 and it is generating tones but those tones are not working properly.. with ptcl and even if i try to decode those tones using mt8870 the ic is not decoding the tones i don't know about how to filter those please mail me too about how to filter or how to make it work
my email is
[email protected]