[aprssig] Wanted: tone-based reset module schematics

[Brad [VE3BSM]]

One of the digipeaters I upgraded to UIDIGI last summer had a small circuit
card mounted in the TNC. I didn't pay much attention at the time, but it
turns out to be a small reset circuit for the TNC. Basically, it listens on
the audio input for a specific tone for 2 seconds, at which point it trips
the reset line of the TNC. It's used to recover from a severe lockup of the
TNC (which it turns out UIDIGI sometimes suffers from). I had to use it once
recently and it saved me from a miserable hike up a snow-covered mountain.
 
I'd like to come up with something similar for the other digis I maintain.
But I haven't yet found any schematics for anything *simple* that does the
trick. I'm hoping maybe somebody here has some schematics, or a pointer to a
site with some.
 
Failing that, when Spring comes I'll hike up the mountain and
reverse-engineer what's up there, though that's not exactly my strong suit.
 
Emphasis on the "simple". This one uses a single tone and I seem to recall
it had one IC (maybe two) and only a couple of discreet components. A DTMF
decoder would do the trick (and be less prone to spurious resets,
presumably), but I really don't have the ability to get into PIC-based
designs.
 
Anybody seen anything like this?
 
Brad.
VE3BSM
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