At 5/6/2010 19:09, you wrote: >Skipp, > >I suspect that you were the exception rather than the rule, then. To me >there are better ways to do it than a 567. I remember playing with various >567 circuits back in the 70's. Never could get reliable performance. Used >them for paging frequencies. Gave up and started using commercial encoders >and decoders and never looked back. Maybe you can give the guy some guidance >to get some stability and choke down the bandwidth so that adjacent tones >don't false the thing.
The problem is if you reduce the BW to +/- half a standard tone freq., the detection time becomes unacceptably long. I tried using them for both DTMF & CTCSS detection a long time ago. Compared to commercial CTCSS decoders, they were more prone to falsing and/or talkoff. Eventually I found a cheap, reliable solution: take a ComSpec SS-32 encoder & add the decode circuitry (the SS-32 & the TS-32 use the same divider/encoder IC). I still have that decoder & it still works just as good as an actual TS-32. Though my 567s seemed to work OK as DTMF decoders, a lot of other people had problems getting them to reliably decode, probably due to the timing capacitor changing value with temperature. Bob NO6B
