DTMF decoder does't work corretly

[miro1024]

DTMF decoder does't work correctly

Hi
(sorry for my poor english)
I use decoder DTMF HT9170d in my project. I connected my device to telephone line - it worked great when it was silence on the line. The problem occured when I was talking on the phone and tried send DTMF code at the same time- HT9170d didn't answer i mean it did not recognize any DTMF(any interrupt on STD pin). Also I connected sin generator on the line and changed frequency. If frequency was between
1,5kHz-2,1kHz decoder didn't answer, if frequency exceeded mentioned range decoder again worked properly.
What could be the problem? Thanks for any advice.

 

[ftcnet]

Re: DTMF decoder does't work correctly

According to the **broken link removed** the noise tolerance is only -12 dB. Is your speech level or sine generator output too high to allow detection of the DTMF tones? There's lots of discussion on this topic at EDAboard. See: problem with dtmf decoder ht9170b

 

[miro1024]

Thanks for answer.

According to the HT9170D specs the noise tolerance is only -12 dB

If I correct convert the -12dB = 0,25. Does this mean the input singnal (speech or other noise) level should not be higher than 0,25 amplitude of DTMF?