[OZAPRS] Maxon DM-2550 and TinyTrak3

Michael Carey michaelcarey at internode.on.net
Mon May 28 17:55:21 EST 2007

Hi Everybody,
I'm turning a TinyTrak3, Maxon DM-2550 and a Garmin GPS-15 into a 
transportable APRS tracker. So far my plan is to jam the whole lot, plus 
a small gel battery into a small Pelican case.
I've made up a small LM-317 based regulator for the DM-2550, providing 
the transceiver with 10V. I also planned on using the carrier detect 
output from the DM-2550 to stop the TinyTrak3 from stomping on other 
It's about here I have come across something weird... I'm powering the 
TinyTrak3 from the same 10V regulated supply as the DM-2550. If I apply 
power to the regulator (connected to both the DM-2550 and the TinyTrak3) 
the DM-2550 goes into a non-operational state, no transmit, no receive. 
I originally thought it was the fault of the DM-2550 and Garry was happy 
to swap it over, but it's the same story with the replacement.
I've got a WXtrak/DM-2550 combo in a half built Peet Bros based weather 
station which seems to exhibit the same problem, but _only_ after I 
connected the CD line of the TinyTrak3 to the DM-2550. Without the CD 
line connected, there is no problem.
If I unplug the DM-2550 and connect it up again, things are OK and will 
be as long as the power supply in maintained. And here is the weird 
part... if I run the combination from a 9.6V NiCd battery pack, I have 
no problems. If I power the TinyTrak3 from a seperate supply (prior to 
the regulator circuit for instance), it's OK as well.
Has anyone in the list seen this problem with the DM-2550 before?
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