MT8880's DTMF receiving problem

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I am using MT8880 and 89c51 in my project.
I can send DTMF out.
however i found that the chip can't 100% receive the correct DTMF signal.
just 5% chance to get the correct tone.

any idea and comment?
thank you for your help in advance.


Re: MT8880's DTMF receiving problem
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You can use a scope to check the input signal for:

- clipping (signal too loud)

You can sample it with your PC soundcard and "CoolEdit" and then do
an FFT to check for:

- (reverse-)twist (one frequency louder than other frequency)
- frequency accuracy (tones too high/low)
- noise (tones don't stand out clearly enough)


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