Tiny stepper motors

If you’re ever in a posh car or on an expensive motorbike, you’ll sometimes notice that when you turn the ignition on, the speedo and rev counter dials do a quick self-calibration, moving their indicator needle all the way round the dial and back to zero again.

Instead of using a traditional meter mechanism (a simple coil and magnet), they use a tiny computer-controlled stepper motor. Here’s one removed from a dial:

The metal shaft sticking out used to have a little plastic indicator needle on the end. Inside, they’re more like a watch mechanism than a traditional stepper motor:

The tiny black cog in the middle is magnetic, and sits in the round gap in the metal frame just to its left.

Power up the two coils in the right sequence, and it drives the tiny cog round, in turn moving the other cogs which move the indicator needle.

These are more traditional stepper motors, though still very tiny:

I dug them out of a tiny camcorder. The shorter one controlled the focussing lens, while the longer one controlled the zoom. The little chip on the left is an Atmega168 – similar to the chip in an Arduino. With luck the chip’ll have enough power to drive the motors directly. Not sure yet what I’m gonna get the motors to do, exactly, but whatever it is it’ll be tiny and very cool. Yeah.

Secret Project #16638


Ever since I found you could get little SMD jumpers (zero ohm resistors) it’s made laying complicated circuits on single-sided circuit boards much easier. Normally if you need a signal to cross over other tracks without touching them, you have to solder little wire jumpers in to form bridges, which means a lot of careful wire measuring and stripping (you can see the red ones above). For little jumps I can use the SMD resistors – the little black oblongs with 000 printed on them. If you’re careful they can jump over 3 other tracks…

LED Boost driver

A friend found a stack of discarded LED assemblies in a skip, and threw them my way. Amongst the other bits, there were several Dialight Lumiled strips – nicely machined aluminium backplates with 6 bright white 1-Watt LEDs mounted on top. They’re designed to be run from a proprietary power supply that delivers around 19.2 volts at a tightly controlled 350mA. So, not the sort of thing you can wire up to a car battery.

I figures this was as good a time as any to start embarking on analogue electronics – gotta dip your toe in the water at some stage. So, after several hours of wading through various “solutions” on Farnell’s website, I came across a tiny little chip that claims to be designed specifically for driving blocks of 6 LEDs like this. The datasheet showed an example circuit along with the specifications of the extra components needed, so I ordered the bits and designed a little board.

It’s a boost driver, which means it can produce a higher voltage output than the voltage you put in. Power in and out are roughly the same, though; so it takes more current input than the current it can provide at the output.

I designed the PCB in Eagle, and used a free plugin/script to convert the pattern into G-code for my mill to understand. Gotta write more about my mill another time – for me, this is where it shines. It took about 5 minutes to carve out this little circuit, much much faster than etching a board in acid, the old way.

Soldering the components on was a little bit fiddly but doable. I find it helps, when soldering multi-legged components like the little SOT3-6 driver chip, to wet all the pads on the board with solder first, using solder wick to remove all but the thinnest little layer.

The board worked first time. Which shouldn’t have been surprising, given that it was the manufacturer’s design, but I never seem to imagine things will go that easily… And the little driver circuit is small enough to mount inside the lights’ cases, too, so I’m going to have to make up a batch of them.

Solar power for emergency use

I’ve had lots of questions from friends about how to set up their own emergency solar system, so that if there’s a power cut / apocalypse / etc they’ll still be able to have lights, radios and phones working. So I’ve put up a page with FAQs and a few example solar setups, from around £250. Cheaper if you already have a car battery lying around – the bare bones is really only about £150. It’s all stuff bought from eBay, and it’s a tiny fraction of what most people charge for a solar starter kit. Check out http://www.shopwiki.co.uk/l/Solar-Technology-80W-Solar-Panel-Kit—Starter – even Maplin are trying to charge £600 for a £110 panel plus a £20 charge controller. And there are shops asking for upward of £800, relying on the fact that people don’t understand how simple they are to use.

So, do it yourself! Don’t get ripped off by buying a kit (unless you buy it from me, in which case why not buy two?).

Check out https://howiem.org/solar for more info. Any questions, drop me a line and I’ll add it to the page.

Orchestral / dub-steppy track

Wrote this while I should have been working. Yes.

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Bad kerning: The Mentalist *UPDATED*

As part of my remit to kvetch about bad typography I had to mention the nasty type-it-and-fergeddit attitude by whoever does the titles for The Mentalist. Had to.

But look – we’re now 4 seasons in and someone heard me!

They’ve nudged the W and the A together to stop people driving trucks through. Look, here’s what it used to look like (for 3 whole seasons):

There are a few other kerning-based atrocities throughout the sequence (and Mr Yeoman’s credit is still a little inconsistent), but they fixed the worst one, yay!

Next question – isn’t it about time I was recognised financially for this service?