Nerdy Texts of Analog and Embedded Systems Wizardry

So, Bent 2010 is over, and as such my arbitrary deadline and excuse for spending time and cheddar on this particular device has been pulled. The above are the final circuits I presented with at the lecture.

The thing on the left is “Color Me Baddly” from the Gerbers below. It’s a color video synth (based on PLLs) which takes a CV in for the color generators (which is peculiar about its input range, to be sure). It also takes a CMOS level input which can invert the color carrier phase by 180 degrees. On the output side it spits standard composite video as well as a CMOS level color carrier (with no sync, blanking, or burst).

The PLL color tracking is pretty good! But not perfect. The PLL keeps lock over a range of a few volts in, and tracks as high as 30+ kHz, which is better than I’d hoped. It took a lot of fudging the loop filter, although the RC calculations weren’t very hard. The invert is a cool input, which originally I just made for the proto because I needed it to to get 360 degrees of color. But in general (not suprisingly) I’m finding that the more inputs you have to things like this the more weird interactions you can get between modulating signals. So I think the invert is here to stay.

The thing on the right is the “Video Mess Tool”. The circuit is different than I originally intended w/r/t the clamping circuits, which had to be made active. The crap you see over in the far right side in the proto area is that new clamp. The clamp ranges changed a little, too. The LT1203 and AD828 and AD8561 are all pretty great ICs and basically do EXACTLY what you’d expect. Even using the opamps in unity gain for the clamps (not recommended) worked without any hitches.

I think this circuit would look a lot cooler with a window comparator — something which muxed many different mess or non mess signals and was smarter about selecting when, and which had a _still_ better series of clamps for restricting signal range. A HSYNC+burst specific monostable following the comparator would also probably not be amiss, although some of the glitchiness would be eliminated. This could be selectable — “sloppy sync” vs “Teutonic Sync” or the like.

The thing in the back is a color synth I made for Christams 2009. It uses varactor diodes instead of a PLL and is its own weird animal. There are pics of that here.

So before finally throwing these guys into the mothballs for who knows what/how long, I made a couple more videos. They showcase some of the more complicated waveforms that can be generated. Neither has any audio involved; both use input from function generators. The above uses the mess tool to mux in a rainbow from the color synth into golf. The lower one is basically two synths being muxed together and inverted all around multiples of 60 Hz, which makes the trippy horizontal band.

Naturally, all this stuff looks better in person; taping an LCD screen with a webcam is not exaclty the height of majesty. And there’s a couple more tech notes on the Narrat1ve youtube channel.

This might be it for this project for awhile, so feel free to write to me or get on the forum if there’s anything else you’d like to know about!

[NOTE: Collin Cunningham of MAKE took a pretty kickass video of my lecture at Bent, and one day I’ll put it up here. Thanks, Collin!]

Xoxo, TB

So you can see this PLL video synth guy working his magick here if you look at the scope. That’s a reference colorburst on the top trace, and the bottom trace is that same signal being shifted back and forth around the reference. That’s how NTSC is fixing to get its hue on.

Doing this is the hardest part about generating a color video signal from scratch. “Real” color encoding devices (in NTSC) use something called “IQ Modulation” (really) or QAM (Quadrature Amplitude Modulation) which is what I will shoot for in the next version of this.

I mean, real devices now use processors and ASICs, but.

A close up of the board after he got stuck on some hot pink acrylic.

xo
TB

Video Mess Tool Version 0.9 is up and running! Peep the videos! There’s one here and more on teh yootoobz. No promises on revolutions/revelations — there’s still lots for me to do to make this device generate cooler output, but the concept seems to be sound.

More nerd details once I’m out of lab mode.

So if you don’t know how low I will sink to make a prototype work, now you do :-)
xo
TB

Yesterday the PCBs for the Mess Tool came in and I populated them. Like a big dummy I forgot to order the LT1203, so testing was relegated to the bench until today. This turned out to be a good thing, since of course there were legit problems which needed attention.
You can see from the pics that there’s a proto area in the mess tool. That ended up being a good thing. Part of the circuit is a set of clamps which let you keep whatever gnarly signal you’re injecting into the poor unsuspecting TV from spilling over into the sync region.

These clamps ended up being the source of some trouble — they were mushy passive clamps which put a 47k in series with a video signal, which it turns out is TOO MUCH, since all that pretty ground plane (and the IC inputs, and whatever other parasitic stuff is going on) contributes significant capacitance at color frequencies. The diodes I was using to clamp to a reference (SD103s) turn out to also have a 50pF capacitance or so at 1MHz, which again, counts for a lot.

This means that the video through the “snarled up” section tended to just get filtered away to nothing. The solution was (well, will be, I’m still building it) an active clamp which lowers all the circuit impedances and generally burns up more current.

The mux came in this morning (and Digikey was out of parts in the correct footprint, grumble) as did the boards for the synth and some low-capacitance diodes. So today will be busy. More soon.

Also. Not to get gooey, but man do I love hardware. Really. I forget that in the good old days it was me and a scope and I never ever wanted to learn to program. You know, when men were men and all that.

Xoxo, TB