dtmfout problem

[lerameur]

I was initially thinking of going with a specialized DTMF chip. They are hard to get around here

[skimask]

I was initially thinking of going with a specialized DTMF chip. They are hard to get around here

I wouldn't think you'd need a special chip...just maybe brush up on some filter design techniques. After all, what you're trying to do has been done probably hundreds of times before. No reason why you can't do the same thing...

And also...

Here == ???????????????

[Darrel Taylor]

I'm not sure what affect it will have on DTMFOUT, but you have ....

ANSEL = 1

Which puts PORTA.0 in Analog mode.
And that's the DTMF pin.

Might try ...

ANSEL = 0
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[lerameur]

that did not work,
everytime a DTMF comes out, its like someone was blowing air at the same time.. from what I can hear from the speaker.
if I choose to do a low pass filter, what would you suggest my cut off frequency be?

[skimask]

if I choose to do a low pass filter, what would you suggest my cut off frequency be?

Well, since DTMF freq's run from 697Hz to 1633Hz (reference Wikipedia), shooting for 1634 would be a good bet, but probably not practical. I'd tend to think that a 'brick wall' above 2KHz would do it.
And I'd also be willing to bet that the 'air' you are hearing is in fact aliasing of the fundamental tone due to the numerous harmonics caused by the square wave output of the PIC.

[Jumper]

Hi,

What do you plan to design the filter? RC? OP-amps? LC? go for a filter chip?

[lerameur]

I dont know yet, but I remember some chip requires +15 and 15- supply , I only have about 6 or 7v supply.
I tried a single stage RC, with 0.2uF and 400ohms, that did not do anything..