After a surprisingly straightforward and pleasing construction and debugging session, the Gumstix is now on the Gumsense mark 2 :-) The Gumstix powers up fine and communicates with the MSP430 successfully.
So far I’ve found two mistakes and two slight annoyance on the board:
- I’d missed a ground connection to the output capacitor and diode of the Gumstix switchmode supply. Easily fixed by a short piece of thin blue wire soldered between the diode and a nearby grounded via.
- I’d done something weird in the Eagle schematic editor. Eagle has an annoying feature that allows two unconnected wires on the schematic to become part of the same net. That’s not so bad – normally I promote using netnames to connect different parts together. The problem is that in this case, only one of those tracks is labelled. So, I ended up with the MSP430 supply being connected straight to the voltage regulator rather than going through a schottky diode first. This meant that the button cell initially didn’t do anything. Fixing this required the cutting of 4 tracks and the addition of 2 very short pieces of blue wire.
- The first slight annoyance is that I’ve put a dual diode (BAT54C) too close to a capacitor. It all fits, it’s just a little tight.
- I neglected to put a decoupling/resevoir capacitor on the MSP430 internal reference output pin. The datasheet recommends this. I’d written it down in my list of things to do before the board went off to made too. For some reason, I just completely ignored it.
So, the blue wire count is now three. Analogue section next.
Posted at 6:55 pm on Friday 30th March 2007
One response to “And then there were three”
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That’s quite an interesting Eagle feature.
You should move to using gEDA. It doesn’t do that. No, you’d get a veritable catalogue of different interesting “features” to confuse and confound you.