> Ah, yes, the (in)famous 567. It could be quite good at > what it was designed to do. The datasheets and application > documentation were actually very helpful.
An Amen from the crowd... > Being TTL compatible they stressed the power supply with > current spikes so a bunch of caps were needed on the supply > buss near the chip. Al, You made me do a quick flashback to an earlier time of "spikes on the power supply rails"... I'd almost buried that memory. > Their main limitation was the TC of the external timing > resistors and caps. Another Amen... I was so proud of the first circuit I built and installed on a repeater, which became intermittent after a few weeks, then stopped working after a month. Turns out the parts had aged and changed value. That circuit received a quick realignment while I built a replacement using better parts. > They would often take 14 or more cycles of the incoming tone > to detect it, especially if this tone was nearly 180 degrees > out from the free running frequency of the 567 PLL. Which is actually quite usable, especially when you have/had nothing in place before that. > (There was a kluge around this using two 567's running in > quadrature and OR-ing their outputs.) There was also more than one method to slightly steer the free running frequency to reduce the detect time. > As someone mentioned they are fairly level sensitive to > the incoming tone. There's a single op-amp audio compressor circuit (driving a clamping transistor or fet) re-drawn and posted in a few places on the web and it's pretty much a copy of the audio agc circuit I first saw parked in front of a commercial 567 tone decoder circuit (back in the 1970's). Of course I copied and used that circuit as did a lot of other people. But I never had to use one in front of a 567 circuit I built. > And they had problems with sub-harmonics. Pretty easy to deal with... If you examine the Hamtronics TD-3 CTCSS Encoder/Decoder circuit I had provided the link for, you'll notice the filter circuit built into the supporting parts of Q1. http://www.hamtronics.com/pdf/TD-3.pdf diagram on the last page. > I used the 567s successfully to decode various tones used > in commercial broadcast applications but these tones were > fairly widely spaced. And many, many hours of R&D were > involved to tame them. > This was in the middle to later 1970's when the 567 was > new technology. I would not dream of using them for > anything serious today. Probably true, but they would still work for the cause if one were motivated and paying attention to the details. Although many of the group members might discount the Hamtronics TD-3 circuit, all things considered it does work fairly well for what it is. So does/did the Yaesu version of the same circuit I have a copy of somewhere in my files. > There are much better options available. Ebay often has > decoders for under $30, sometimes less than $20. Yep, Ebay can easily discourage building anything from scratch. > 73, > Al, K9SI cheers Al, skipp
