[aprssig] Wanted: tone-based reset module schematics

Robert Bruninga bruninga at usna.edu
Tue Feb 7 08:36:17 EST 2006

Actually, this is what PCSAT uses too.  A simple
555 timer with a transistor hooked to the PTT line.
If it doesnt get hit once every few minues, the 555
times out and resets the TNC>..

>>> ron.tonneson at gmail.com 02/06/06 10:29 PM >>>

I have a design that I use on my digipeaters.  It is not quite that simple but it does the same job and does not need 
you to do any tones.  It monitors the RF output of the transmitter, if is stays on to long or does not come on at least 
once every 12 minutes or so it will cycle the power to the radio and TNC.  My design is documented on the Yahoo UI-Digi 
group at: http://groups.yahoo.com/group/uidigi/files/APRS%20Monitor/ If you are not on that group I can put the info in 
an email attachment for you.

Ron - K0QVF

Brad [VE3BSM] wrote:

> 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.
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