Nerdy Texts of Analog and Embedded Systems Wizardry

Sorry for the short posts. These are long days.
The real dancing stand controller boards are here!

The real magnetic position sensing encoders, too:

The other side of those encoders is a magnet (read the datasheet if you’re curious — these parts are expensive and awesome and totally worth it), and that magnet has to be centered very precisely over the IC. Any eccentricity or slop or variation in Z height will make for bad accuracy. You wouldn’t guess from the datasheet but these parts are actually pretty forgiving. Nonetheless, I had a buddy of mine (Joe, over at BreadBox Studio) turn me some ABS magnet holders which keep the magnet aligned with the shaft of the stand. They also space the magnet off the shaft itself (the shaft is steel and screws with the magnetic field as the encoder wants to see it) and provide some registration holes. The magnets are press fit into the ABS turnings. Like so:

Thanks, Joe! Now I gotta crank out 17 and make sure they all do what they should. Wish me luck….

So Cory has a bigass show coming up at the Whitney this summer, and I’ve got SEVENTEEN!! dancing stands to build. They’re different from the last batch in that they have to run synchronously. The idea is to use a PID control loop and sync them via RF. They run on steppers, mostly because it was easy to find steppers that were torquey enough for the application and still fit under the dancing stand easily. The MCU is an Atmel, the RF link is by LINX, and the stepper driver is a TI DRV8xxx part.

Here’s the protos:

The system has a lot of slop, and I decided to do positional feedback using an absolute position sensing magnetic rotary encoder. This one is by Austria Microsystems. The specs on these are INCREDIBLE, but mounting them takes serious care to get that accuracy. I made a bunch of jigs, you can see this one all strung up under the stand’s driven leg. We’ll see how well they work…

Oh, yeah. And we made more bowling controllers. Or mostly my assistant Daniel did. These guys are really getting pretty cookie-cutter:

I feel pretty good about the protos of those stands, but my crystal ball predicts something will be screwy. We’ll see.

I went to Tokyo with my GF’s family over the New Year. It was, in a word, OFF THE CHAIN. The above is a stall in Akihabara, which defies everything I know about retail shopping. In a bin, hanging out like so many gnarly street fruits, are op-amps, AVRs, weird eeproms, name it. It was crazy. And there were streets of these. As if that wasn’t enough:

That store just sold stuff with threads. If it had cut threads, you could buy it there. If it did not, you couldn’t. Why not? I got some bags of clear polycarbonate metric machine screws, cause hey, you never know when you might need THOSE.

Obligatory picture of 5G, one of the worlds most awesome synthesizer stores. This is the tech bench. You can tell because it looks like a messy-ass tech bench.

So, because it isn’t actually in a show yet I can’t talk about what this new dancing stand is for, but it may or may not be capable of beating up Robocop. Suffice it to say, the old gearmotor has been removed from this stand and replaced with a two-pound tank which comes as a separate synchronous motor and gearhead.

This also continues the fascinating if slightly worriesome Spring 2010 trend of my clients viewing me as a one stop for assembly language and abrasives, but things are slow so I’ll take it.

The new gearmotor was similar in size to the old one, but not so similar that it didn’t mean cutting out a big piece of the steel doghouse, making some aluminum mounts to hold the motor, drilling out the timing pulleys to fit the new motor shaft, and putting a detent in said shaft to seat the set screw. I also got my first set of metric taps, so that I could use M4 screws in this guy and the hardware I put in would match the hardware from the factory. This, O art world, is the attention to detail you get when you hire C Programmers to get their thread-cutting on.

Here she is all buttoned up.

Though I have a sneaking feeling Cory doesn’t really care about what the bottom of these things look like, I kinda do. Plus I figure the dust cover, you know, keeps dust out. Plus I had just gotten these really cool carbide burs and I was excited about cutting more holes in stuff.

Perhaps one day, one of these things will have a stepper motor or optical encoder or SOMETHING with silicon in it and everything will come full circle.

So a few weeks ago I met up with my old buddies Limor and Phil at Adafruit Industries and was griping about work being slow, and they were like, design us a kit.

So I did. They wanted a headphone amp which, in their words, “didn’t suck”.
This was really exciting to me! I do a lot of contract work, but I almost NEVER get to do something that’s exclusively analog! Granted, an HPA is not exactly pushing the boundaries of silicon magic in 2010, but I’ll take what I can get. It was a blast. I got to figure out phase margins and characterize ringing and overshoot and make a cable mess (and then worry about the capacitance of it) and just generally get my party on. Plus it was a chance to flex skills in an arena that is full of a lot of crappy designs.

And though the thing is GPL’d,, they did ask me not to go into specifics here or post any schematics or juicy bits UNTIL they have the product out, so until that happens I’m afraid I can’t go into a lot more detail.

Can’t wait to see them lay it out.
Thanks guys!

ALSO — I’d be remiss in not mentioning my friend Shea who had a lot of great advice on this circuit and who has generally forgotten more about audio electronics than I’ll ever know. He re-did the Trident A Range board at Soma Electronic Music Studios when I was back in embedded diapers and let me help re-cap some modules and generally be a solder monkey. I got paid $10 an hour for that and those were still some of the most exciting electronics dollars I ever made.