Gil Simon wrote:
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I have to dial the numbers also, so I can't use 8870 as is only receiving IC.
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Hi,

Try using some good quality filters in the inputstage!!! (active filters??). detecting tone is not an easy job,but not even impossible you can check easily the
input bcd by toggling an LED?.
If you are detecting something then it is
fine now the sure problem is the presence of 6th order harmonics do one thing
make two 6th order BP filter with switching Capacitors and place it in the input stage
this will give you very nice crystal clear waveform ,if thistime it doesnt work then
Please take out your car keep secretly the chip in your pocket go to a nearby railway
line and carefully stick it in the track with some tape and ask it to work or else you
will leave it there :)).





sanjeev