🚀 go-pugleaf

This comes up now and then and I'm always interested, but no one ever
seems to come up with a definate answer.  I'm looking for a schematic
for a touch-tone decoder circuit.  Something that simply takes audio
input and lights an appropriate LED for 0-9,#,*,A-D when it "hears"
it on the audio line.  I've done this project with a bunch (12-16)
seperate tone decoders and then used AND gates, but as everyone knows,
it's not a very good design and it is very sensitive to false readings.

I'd almost given up hope and forgotten about the project for a while when
I recieved the new All Electronics catalog (#492)...  One of the items
offered is some "revolutionary toner-transfer paper" or something.
Anyways, the picture included next to that ad is one side of a pc board
etching -- and the title is etched on it -- "TONE DECODER."  If you
look real close, you see that they are using one main chip (24 pins) to
decode everything (include 0-9,#,*,A-D), so it must specifically be for
decoding DTMF!  Now, if anyone happens to know what this chip is (and
can provide me with a nice schematic since I'm just a beginner and even
with the chip I would have a difficult time making anything useful), I
would _GREATLY_ appreciate it!  I've been wanting to have such a device
for quite a while now and have heard from many people along the way
stateing that they are also very interested.  (Note!:  Please don't
mail me and ask for me to forward any answers to you -- when this
happens, the only responses I receive end up being 20 requests for
teh schematic that I never get... -- In any case, I don't mean this to
be rude, it just won't help any -- I PROMISE that I WILL POST a summary
of all the valid responses that I receive.  So, everyone can get the
answers just by reading my final summary without having to post to
request that I mail it directly to you!)

Advanced thanks to anyone who can get me any information about this
project!

Talk to you all later...

 - John Goggan (34ii5mt@cmuvm.csv.cmich.edu)
               (or NeXT-Mail at:  john@opus.csv.cmich.edu)