Tuesday, January 13, 2009


We had a little scare tonight.  Bryan was busy all night memorizing the Gettysburgh Address for a history test tomorrow, so I was fiddling with the power bus board trying to get it in my head how the STAMP microcontroller was going to control relays to power the different components.  

Well, in the process of prototyping the connection, I got two wires crossed and when I powered up the APRS board, instead of activity lights I got tiny "Psspt" and an ever so faint wisp if smoke!  That's not good.  As my engineer friend always says about electronics, "The trick is always keeping the magic smoke inside!"

I de-powered immediately and saw my mistake.  After correcting it, I checked the operation of the APRS board and it failed.  It would no longer power up.  Uh oh.

I went and fessed up to Bryan and wrote the owner of Byonics for advice.  Fortunately I got an encouraging response:

"There is a small glass diode mounted near the tab where the RF metal can sits. Just use a pair of nippers and cut it off. This is the reverse polarity protection diode. "
Basically the circuit has a small diode to protect the more expensive parts in the event of a backwards connection.  It dutifully sacrificed itself to save our board!  We will replace that diode before applying power again, and it will give Bryan and I a chance to discuss how the protection circuit worked.

Whew, that was close.  I think everything gets a diode now!

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