I had a slow week this week and laid out and ordered a “bare metal” PCB for an ARM Cortex M3 — the NXP LPC175x series. I spend too much time messing with 8-bit MCUs. It’s 2011 after all.
I brought up an ARM7TDMI awhile back, and figured it was worth at least trying to stay current. One of these days I’ll populate this guy, and eventually hopefully even program it.
A very exciting day! It’s like this:
…and like that:
and like this and uh:
These are the gerbers for the new WTPA2 and its Flash daughterboard, and the REAL THINGS fresh off the jet from Advanced Circuits! The new kind-of-questionable-but-kind-of-awesome through-hole SRAM got here also:
So these all can go together today!!! There’s a ton of new firmware that I’m still working on to support new features, so we may not hear any crusty samples, but I’m hopeful we’ll get to see some lights blinking at least before sundown. It’s da future!
Stay tuned,
xo
TB
Just for grins, while I was waiting for the PCBs to come in, I decided to lay out a new design for color synthesis that I’d been fooling around with. This, again, is the gerber file.
The sync and blanking circuits in the above are fairly pedestrian — they’re just an AVR running at 14.318 MHz, which controls a 4051 to gate in the correct resistor values to get sync and blanking levels into 75 ohms. This part is pretty much exactly the same as the circuit from Owen Osborn’s old CA synth (which is a really elegant piece of engineering, I think). The AVR generates the colorburst and color carrier also using a hardware timer to divide the crystal frequency by 4. This means this prototype ain’t gonna do PAL. Sorry.
To my mind, the really interesting thing is the way in which color gets generated. Hue is encoded in analog composite video by _PHASE SHIFT_ of a carrier wave. Someone very smart and very good at electronics figured that out a long time ago. I’ve built synths in past which use the AD724 (lame) and varactor diodes to give continuously variable integration.
The varactors are actually a pretty badass way of doing it — they’re fast and kinda nonlinear and totally work, but it requires A LOT of stages of this to get 360 degrees of shift (enough for all the colors a TV can display). Also, (in addition to not being super cheap) the really good varactors are small SMT devices. I personally don’t care, but some of the cave-people with soldering irons who frequent this site occasionally express concern about this sort of thing and their poor tired eyeballs etc etc. Generally when this happens I turn up the Brandenburg Concertos and have my manservant pour me another Campari spritzer, but this time I decided the unwashed masses should have some cake too.
So.
It took a lot of searching and fiddling to find something that I thought would work, that was both elegant and cheap and didn’t require exotic components or a sensitive board layout or weird supply rails or whatever. I had this suspicion that a PLL could do what I wanted, cause you know, its job is to party with phase. PLLs regularly work at or above colorburst frequencies (3.58MHz) which is also good because it means they aren’t on the edge of some spec.
The other idea I had (a voltage controlled all-pass filter) was generally too hard to do at frequency ranges that high (the LM13700 won’t slew anywhere near that fast, for instance). Other than designing an OTA which works at those frequencies (on my list of things to do, along with dating supermodels, designing invincible armor and generally running Stark Enterprises) I wasn’t sure how to implement this in a simple way.
PLLs are not the easiest circuits to understand (for me, anyway). But they are cheap and ubiquitous and many very smart people have written a lot about them. Eventually I stumbled across this circuit in EDN. The description with it is brief, but pithy, and explains the essential details of what I wanted to do.
Armed with this I was able to create a new design, standing on the shoulders of great nerds past. And when UPS shows up, I’ll know how well it (as well as the Mess Tool) works out!
Xoxo, TB
The pretty pretty gerbers for a new video tool. This device will hopefully allow you to take all the precious bits of composite NTSC (or PAL, I guess) video and keep them safe, while mucking with the rest of the signal. Sync, blanking, and colorburst are separated with a level comparator, and a mux allows you to inject new signals or perturb the old one. It’s analog, and based on the AD828 op amp, the AD8561 comparator, and the LT1203 video mux/buffer. For one, I hope it works. For two, I hope it looks awesome. Stay posted!
God, it’s been so long I hardly know what to say. But I believe the big banner above says the most important thing :-)
It is with excitement and not a little trepidation that I am announcing WTPA’s booting out of workbench land and into the hard, cold world.
That’s right: The wait is almost over — the real deal kits WILL BE out for the Bent Festival in New York this April! Not my usual, waffly “soon”. But on a real, fixed, finite date!
That’s exactly one year since the proto came out, and would be embarrassingly slow if the latest WTPA wasn’t head and shoulders better than its forefather. But. Lest you think I’ve been idle, know that since my last post I have done several things:
The first run of kits will number 0-199. This figure made the most sense considering all the number crunching I did, at least for now. The retail price will be announced on or around the release date, but for the curious it will be nestled snugly somewhere between Mssrs Grant and Benjamin.
There may, at some point, be another distributor besides Narrat1ve for this kit, but they will not likely be onboard by the release date. The kit will come BYO-enclosure, although I will probably sell some parts on the site to make it easier for those of you who want a little of the guesswork taken out. The website will (has to, basically) get beautified to accomodate info for the people building the kit, and not so much my gibbering. Finally, on (or right around) the release date, you’ll be able to get ahold of the source, schematics, instructional videos, manual, and theory of operation docs all from right here.
The hot mess you see above is the test pressing of the final WTPA boards (it’s a picture of the gerber files, complements of GEDA’s Gerbv, which (sadly) unlike most of GEDA, totally rules). The real thing gets here Monday for requisite twiddling.
This is the third and last (hopefully) major hardware revision WTPA will go through. The second WTPA totally slayed the first in audio quality, latency, functionality and pretty much everything else. This last rev cleans up the rough spots that were still left on the second rev, and adds a sprinkle of small new features.
Mostly, however, it is the physically smallest and most simplified of the WTPAs to come out yet and is geared to make the kit easier to build and cheaper to sell. There is very little fat left on this design in my opinion.
Technically, WTPA has returned to single-MCU design. Shortly after I made the two-MCU rev I learned about a device called an I/O expander, which is cheaper, simpler, and more robust than a goofy UART link with a second MCU. Shortly after beginning to do battle with the I/O expander I did some much needed forehead-smacking and figured out how to rearrange the databus and replace the whole nasty expander / MCU / mess / with another parallel latch. Which of course was the Right Answer. Pie-simple, cheap, effective.
This WTPA also has its two analog subsystems (the input/output amps and the VCO / CV section) isolated with separate ground planes and ground returns to the main regulator. The last WTPA was not noisy, but I expect this one to be even better. The goofy emitter follower in the front end has been removed. This should result in better audio response, more headroom, and fewer parts.
The jitter generator has been moved into the realm of software. This does a lot for us. Most importantly, it makes the jitter work right (and sound cooler). It also introduces less HF noise onto the board, and further reduces the parts count. Finally it allows the jitter to be controlled by MIDI! This is obviously good for playability reasons, but it’s “orthoganally good” as well because the jitter clock was the only effect left exclusively in the analog domain. Other than the gains, everything on WTPA is now controllable from both the knobs and switches AND the MIDI in.
Finally, all this hardware juggling allowed me to free up a few extra pins which I assigned to a spare UART / SPI module. I have no immediate plans to expand WTPA, but if I ever did, this would be a great way to do it (say, to talk to other instruments or to add an SD card interface or the like).
This all means that the hardware is basically done changing. It also means I’m getting down to the wire on software business, too. WTPA will not go gently into the aforementioned good night — expect to see LOTS of updates here for the next month while I pull all-nighters getting this monster ready for her catwalk. There will be some ugly fixes, a huge rush of features, sample banks, scope traces, the whole nine. Exciting stuff!
And hey, thanks so much for sticking around this long. Xoxoxo.
