First beta WTPA 2 release date got announced on the Narrat1ve Forum today. I promise to have pictures of a more-or-less-working printed circuit board HERE by July 1st. I’ve already got a rep at Future who I think can save me some dough in parts sourcing, which is good, and I’ve got initial hardware specs (RAM, rotary encoders, new MCU etc) done. The board is starting to come together too. Once all that happens the firmware will start to get changed and I’ll make sure the pretty case fits and looks nice.
Normally I hate solderless breadboards, but I was kindof inspired by doing recent work with Adafruit that they were OK for iterating through low frequency, proof-of-concepty kind of stuff.
And a good thing I was, too. WTPA2 was slated to have a VCO as a sample clock source, bringing that feature back from the murky WTPA v0.98 days. However, a standard 4046 clock had some troubles, at least as I breadboarded it.
Using a 5v supply, and a CV at the VCO input of 0-5v, and varying the values of the VCO resistors and caps I wasn’t able to get much better than a decade of frequency out of the part. I scribbled these numbers all down on various post-its that no longer make a lot of sense to me, but getting an FMax of 20KHz and an Fmin of <100Hz seemed pretty much impossible, both experimentally and once I bothered to do the math problems in the datasheet. Moreover (and I'd seen this before with the 4046 in video synth stuff) once the CV gets too close to 0v or too close to the positive rail, the oscillator tends to either stop or jump up in frequency.
If you haven't already, it's worth referring to the 74HC4046 datasheet while reading this pontification, at the very least to convince yourself that I am not totally making this up.
This is not the most rigorous breakdown, I know, but it was enough to convince me that a standard 2 resistor, 1 cap, and and CV style 4046 VCO was not going to hack it without some kind of magic. I’d been curious about the LM331 V-to-F so I got its datasheet and did some more scratchpad math and convinced myself that it was a lot more likely to come close to what I wanted without serious massage. It’s quite a bit more expensive than the 4046, but at least it’s physically smaller.
So one of my clients (Holly Hunt) was gearing up for a big week at ICFF and installed this Solid State Chandelier I designed for them. In nerd terms it’s basically a collection of individual light elements which have a handful of Aluminum core PCBs running these kickass high power LEDs. Nothing complicated, although it had to pass a bunch of UL stuff and required some fiddling with thermal management. And making Aluminum PCBs which I hadn’t done before.
Anyhoo, the chandelier came in to their showroom and was all kinds of screwed up. Turns out it was (mostly) just some solder pads that got lifted in transport, but it was pretty stressful for about a day. I schlepped out to Midtown and fixed it, and spent a lot of time worrying about getting solder (or nerd cooties) on really expensive couches made of goatskin and whatnot.
The pic above is the chandelier hanging precariously on some support chains so I can work on it. All the acrylic has been removed.
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!]
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.
