LED Controller board, rev. B

I tried checking out the new (rev. A) controller board earlier this week, with no success.  A bit of diagnostics showed that the ground layers weren't switching and further research provided the reason: the SOT-89 package for the transistors didn't match the pins of other packages for the same device.

I'm not sure how I ended up making this mistake, though I suspect what happened is that I originally did the schematic assuming a different package, and failed to verify the pinning after making the change.

The picture shows the cube with the prototype boards (brown), with the SMT rev. A board behind (green).  Mostly for a size comparison.  Unfortunately, there probably aren't any packages of similar size and matching pinning that I could use to replace what I have.  This means that I'll have to make another order of boards, which will at least have all the tweaks I've done since learning from my mistakes on the rev. A board.  Hopefully, there won't be further mistakes requiring new boards as at $100 per run, the cost adds up in a hurry.

Mad "Scientists"

I think I now know why the "mad scientist" archetype in movies and such always has a maniacal laugh when they achieve their goal.  It's almost compelling, really, and it has little to do with madness.  That sense of accomplishment at having achieved a goal towards which a great amount of effort has been put is quite an emotional rush.  Last night, I populated my LED cube controller board as much as I could.  Today, I turned it on for the first time.  While it didn't work 100% perfectly, I was at least able to program the microcontroller and verify that the start-up sequence was working properly.  This is a bit like building a computer from scratch (and I don't mean by ordering a motherboard and such, I mean by building the motherboard yourself) and turning it on and seeing it go through its boot sequence for the first time.

For me, it was a major accomplishment.

The project is far from done.  The empty spots visible on the card need to be filled.  In fact, that's one of the first of several mistakes that have been uncovered in the design.  The original parts meant to go in those locations turned out to be too large to fit.  I've since found a suitable replacement which I should be receiving tomorrow.  Before that, I received the parts kit only to find that the black switches were not, as I'd inferred from the data sheet, illuminated (the white button is, however, a nifty but expensive control).  I've also found that I drew the traces to the ISP (programming) connector incorrectly (which I worked around by running wires from the connector to the right pins on the programmer), the pads that I drew for the filter capacitor (bottom right, glared out orange piece next to the power connector) were less-than-ideal, and there wasn't quite enough physical space between the switches.  Also, I didn't quite solder one of the components to the white push-button well enough but that was very easy to fix.

If I do end up having a second revision of the board made, I'll almost certainly replace the 0402 devices (mentioned in an earlier post) with larger, easier to see, easier to manipulate, and harder to lose 0603 devices.  I can now say "I did it!" (WRT those tiny devices), but I can also say "I don't want to have to do it again!"

The Realm of the Tiny

I've been working for the past few weeks on a surface mount version of the controller circuit described in this instructable for an LED cube.  "Surface Mount" means that the electronic components are soldered directly onto copper "pads" on a printed circuit board, as opposed to "through hole" devices, where a wire or lead goes through a hole that goes all the way through the board.

I've just soldered (properly, this time) two "0402" package capacitors onto the board.  This package size describes devices that are 1mm x 0.5mm (0.04" × 0.02").  After finishing those two pieces, I kinda stared, wide-eyed, at it all.  The accompanying picture shows the result.  I left a needle on the board for size reference.  The needle is 1.5" long, and it was really too big to be of much use holding the component in place.  The components in question are actually probably pretty hard to see, even in this close-up picture.  The needle point is close to the center, just above the label "C5", and the component is just below that.  The two silver dots are the pads and the little brown bit in the middle is the capacitor.  The second one is just above the "C4" label.

Work is still progressing on populating the board.  I'm probably not going to do any more on it for a few days as one of the parts I ordered turned out to be too big to fit on the board the way I designed it.  I've ordered a smaller replacement that should fit, but the uncertainty keeps me from doing much more work.  If I do get the urge to work on it more, I'll definitely check the pad layout very carefully against the specs for the new chip.

Congressional Science Policy

Step 1: Cut funding to scientific research
Step 2: Cut funding to scientific research
Step 3: Cut funding to scientific research
....
Step 15: Eviscerate scientists when they fail to predict destructive weather.
Step 16: Get reelected thanks to your tough stance on.... whatever.