Nerdy Texts of Analog and Embedded Systems Wizardry

So sometime at the beginning of 2010 the sick children of Chicago set up a fuss looking for their monster again. You could hear them all the way from Brooklyn. Again, my guilt was heavy. Again, I made some stuff.

An introduction of what Remoc does is in order I guess. He’s basically a bigass toy that senses when little kids touch him in different spots and plays various games with them. He laughs, he cries. He may or may not be better than Cats. He also goes to sleep at night, sings songs, and has a weird interactive thermometer. He farts a lot. When he behaves, he’s kind of fun.

His memory and play pattern live on an SBC designed by my buddy Todd Squires which we used at the old toy company and affectionately call the toybrain (version 4). The TB4 was fine.

There was no real way to salvage most of the rest of Remoc’s old brain. There was a crappy class AB audio amp I put in which got way too hot, his touchsensor circuits were noise prone and also temperature sensitive, and his LED supply tended to go out of regulation when too many lights in the thermometer stayed on, and he got confused easily about time-of-day stuff if you turned his supply off. His eyeballs were light bulbs which burnt out (that was a committee decision, but). None of this was good.

His new brain boards (above) dealt with all this stuff. 2010 saw Remoc get new MOSFETs to run all his lights, a new audio amp, and a proper RTC with a ginormous battery for backup. More importantly, he got a bunch of precision opamps and a multichannel ADC to handle input from the touchsensors.

The touchsensors were actually fun to make. They’re an AVR which generates a crystal derived square wave (laziness on my part, and tunability. The generator could have been a logic gate or any crystal clock circuit really, although the programmable chip provided fudge room which I didn’t [and hopefully won’t] need) and drives it through a resistor to whatever gnarly sensor plate you have, and then filters and rectifies what’s left. They use hand capacitance to form a variable RC filter; the output of this device is a voltage which is inversely proportional to the capacitance at the sensing node. Not perfect, but pretty good. These sensors also use 1/8″ cables to carry power, ground, and signal, cause 1/8″ cables are cheap and promised to make wiring the beast a lot easier.

The thermometer. Some SMT LEDs on a stick. Yaaaawn.

All this stuff got packed up to schelp to Chicago.

So over the last couple years I’ve been building different variations on this thing for my client/buddy Cory. It’s had many names but the one we tended to call it the most often was the “Video Game TiVo”. It’s basically an AVR with a ton of Atmel Dataflash as well as some Vregs, level translators, and RS-232 chips.

The idea with these guys is that they sit around on a video game controller and log what the user is doing, and then spit that biz back out when you tell them to. The original ones simply hung out watching or asserting the actual switch lines using WPUs and the like, and as time went by they began to actually replace the controller interface entirely and deal exclusively with serial. Depending on the game system, they can sometimes play a game back deterministically, but mostly not because of RNG and/or timing issues. Either way, they’ll record MONTHS of game and can loop arbitrarily, etc etc. They also have a fancy terminal built in for communicating with a PC and recognizing different video game consoles.

Cory wanted them so he could throw infinite gutterballs in Playstation Bowling games. They do that just fine :-)

This one was tested on a PS1 and the canonical bowling.
This January I had geared up to finally make a TON of them so Cory could just have them handy and not need to call me when he needed one, and this was the final test run before we went into production.

Though she probably would have been more interested in a Steven King book and some Calphalon pots, I decided to build a video synthesizer for my Mom for Christmas. I also built one for my girl, who is generally more into blacklights than mom and one for me, because, you know, ho ho ho.

There were lots of reasons to do this. Partially because I think it’s cool to give gifts you make and less altruistically because I was still geeked about the little varactor synth that I’d made and wanted to do a new revision of it.

This synth still generates all the housekeeping signals with an AVR (as well as the colorburst) and switches them around with a 4051 multiplexer. However, it adds a clamp circuit which allowed control of color saturation (the old version was fully saturated color all the time) and a DC offset circuit which controlled brightness (that knob was also at 11). Those circuits worked _OK_ but not great, and I found I generally liked the results when everything was full out. There’s also an option to invert the color carrier, which WAS cool, in an epileptic kind of way. The sync signals on this guy were not _quite_ at the right levels either.

The idea is basically the same as the last varactor synth; except there are now multiple stages of RC phase shift. Each stage uses a SMV1255 “Hyperabrupt Junction Tuning Varactor” as the cap in that RC which is driven by a control voltage. Each stage is also buffered by an XOR gate, to square the signal back up after passing through the RC. One thing I also screwed up in this design was running the chain of buffers NON-INVERTING. This meant that with big phase shifts (which also meant big attenuation from the filter) the color carrier would eventually disappear, I assume because of the asymmetrical thresholds in the gates. On a scope you’d just see the duty cycle getting farther and farther from 50% and then just disappear entirely. The big solder mess here shows the workaround I did to fix this, which helped. Using comparators would help even more. Using a different circuit topology entirely would prove to be the most helpful….

Still this synth was pretty cool. Because it was for Moms and GFs, it was designed to be standalone and not require any inputs. There’s a little prototyping area where I made some function generators to make repetitive waveforms to drive the various color stuff.

xo
TB

My first winter in Brooklyn I made this biz. It’s a video synth that I put together on a little Narrat1ve-specific protoboard (or as I call it, the Narrat1ve Big Wizard). It’s different than the last one in lots of important ways. It’s NTSC, and generates all its own sync and blanking pulses in software (that mess is coded in C for the AVR). I spend a lot of time looking at Bruce Land’s stuff, as well as the always-on-point Owen Osborn.

More importantly I figured out how to get a continuously variable phase shift of the color carrier (analog color!) using varactor diodes! This was a big step in making stuff that looked cool. Varactors are not ideal in a lot of ways, but they are sure simple.

I slapped this guy together for a talk I gave at La Superette that I got asked to do by the inimitable Kyle and Tali from Lovid. They were really cool about this talk and I had a great time!

This really beautiful and simple proto has since been deprecated by the monsters II’ve made since and is hanging around in some drawer or other. Sad, really. Ask Too $hort about it.

xo
TB

This labor of love and money was also for Cory. Basically, there are these two weird Chinese merchandise stands that get sold at places like Spencer’s, and Cory was like, make one go a few percent slower than the other one. I think originally he was thinking stepper motors or something which is why I got involved, but it was a lot more low-level (in a wedge-screw-pulley-inclined-plane kind of way and not so much an assembly language kind of way) than that.

Inside one of these things is a reversible synchronous AC motor with a toothed belt linkage. A quick test with the Variac proved that, yes, their speed was independent of input voltage. Turned out the easiest way to get the speed differential was to pull the original transmission parts and replace them with XL drive pulleys and belts. The OG stands use a 3mm (I think) Chinese pitch system which is kinda hard to find around these parts. McMaster saved the day as usual but now I get my goodies from my pulley people at B&B Manufacturing who have likely forgotten more about power transmission than I ever hope to know. One thing about McMaster, they aren’t shy about leaving other peoples’ labels on their parts :-)

Doing this meant a lot of cutting and tapping, which is fun for me because I rarely get to do it professionally. To wit:

I had to drill out the pulleys (they’re made for 0.250″ shafts and the shafts in the stands are 7mm) and got all noided about leaving tap magic on them because I was worried about the belts not liking it. This was part of the washing/drying process and won me zero points with my housemates.