Sunday, June 26, 2016

Holocircuit progress report

Well, it mostly works.

The Kapton tape arrived Saturday, and I opened up the reflow oven. Yup. A bunch of cheap paper masking tape in there. Removed all of that, replaced it with the Kapton, closed it back up. And the oven worked fine the first time, without any bad smells.

On the bad side, turns out I'd gotten a syringe of solder flux, not solder paste. And was surprisingly hard to determine this; almost all the available information and reviews assumed you were looking for flux, and explained in detail all the ways it was a good flux. And every now and then there'd be a "...and for soldering" which was vague enough to be misleading. So I won't need the oven again until a syringe (or jar) of the real stuff gets here.

Well, with the board properly fluxed and all the components stuck down, it was really no problem to go around and run some solder on to all the components with an iron. I only got one solder bridge -- although, here, the oft-lauded solder wick method completely failed to work and I had to use a solder pump to remove the excess solder.

USB through-connection worked; I was able to access a thumb drive. ICSP worked; I was able to upload the software from the previous holocron (after wasting some time replacing the ATtiny45 with an ATtiny85 -- until I realized I'd already known I needed the larger program memory of the latter, and had in fact ordered and soldered in an ATtiny85 in the first place.

I also had both LEDs the wrong way around but after that got a clean power indicator and charge indicator. And the LiPo charge circuit worked like a charm, successfully charging the battery. The mercury tilt switch did its job as well and the capacitance sensor is working even without the antenna and the NeoPixels did their magic.

However. The last part of the load sharing circuit isn't working. I've traced and tested all the leads, gone back to check the circuit and the pinout, even swapped out the MOSFET and did a new clean solder job. The MOSFET isn't switching; the LiPo won't connect. So I'm a bit depressed right now: I don't have any good ideas as to why it isn't working. It's a very simple circuit, described in at least one brochure. About the only lead I have currently is that the MOSFET I'm using may not actually be the optimal one -- but I'm not really sure which specs would need to be different (plus I'm not happy about having to table work on that part of the circuit until another order can get here from DigiKey).

And as poorly as I'm feeling this weekend, I know it will be a long week in hot weather (and things are a little tense at work; sales are down and we've had to lay off some people). In short, I'm unlikely to be particularly brainy next week. And I'm also realizing just how much programming I want to do on this circuit before it is ready to ship.

Not to mention the physical layer. Finishing the artwork for the laser engraver is going to take a bunch of hours yet. And although I've figured out almost everything else, I'm caught in a nasty little loop trying to find some way to make the 1/8" magnets fit properly into laser-cut slots in the nominal 1/8" acrylic.

Yes. Acrylic (like baltic birch plywood, oddly enough -- and I'm sure there's more) is manufactured in metric. 3mm estimated in this case, caliper measured 2.98mm for the piece I cut last week. And then it is sold in Imperial.

Unfortunately neither magnets nor even ferromagnetic material (aka stainless steel) is commonly sold around here in small metric sizes. And you can't grind down a magnet (not that I want to; there's too much labor in this thing already for the price point I'm trying to hit). And I can't even engrave the difference on the laser, because the needed slot is on the back side to where I'm making my other cuts from, and the software on the new machines has a rather critical flaw when it comes to lining up multiple elements that way.

Oh, yeah. And until I solve that, I can't even cut the final shell piece, meaning I can't go ahead and start painting up shell elements of my new prototype.

I'm going for an oxidized, strongly weathered copper/brass for this one. Star Wars is a used universe, after all. Basically, I'm making the "hero" version of what was seen in an animation.

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