[aprssig] Re: APRS Standard Connectors?

Scott Miller scott at opentrac.org
Wed Nov 30 11:55:51 CST 2005

> I guess if the pin is typically an output and the voltage available
> would seem to be just a "stuck high/low" condition it would be fairly
> safe.

Right, the key is to stick with RS-232 compatibility.  The spec allows +/- 
25 volts.  As long as you keep the signal directions right, everything 
should be OK.  Having the handshaking lines stuck high doesn't hurt anything 
since you're not using them anyway.

I did run into a problem with one OpenTracker test board, where the 1-wire 
bus was provided both on a modular jack AND pin 7.  In diagnostic mode, you 
can have it query the bus for all device IDs and output them to the console. 
But even with handshaking disabled in the terminal program, I found that 
having the RTS line going nuts with 1-wire bus traffic caused weird 
dropouts.  The fix for that board was to cut the trace to pin 7.  Presumably 
in units that don't have the modular jack you'd have a custom cable with 
that line split off to the 1-wire devices, so it wouldn't be an issue.

Scott, N1VG

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