"The tuner display and drivers would be in a separate enclosure that could attach to the top and back of the main box for a unified main console, or alternatively be detached and placed anywhere in the desired sight line on the floor or a separate stand. The tuner could use a short or long cable as needed. I don't currently use any visual tuner, but I want to build it anyway, and for it to be of any use at all it needs to be placed where I gaze while playing, which is not toward the main console.
Your thoughts on this?" - Roger
I never got past the very beginner stage on the two previous Theremins I've owned (EWS, Theremini) so it's difficult for me to know how a more experienced player such as yourself will react, both short term and long, to the various features on the prototype. I remember having a lot of difficulty with finding initial pitch & staying on pitch, and felt the pitch field was just way too sensitive and non-linear. For me, ~1/3 sensitivity feels about right, and this, combined with linearization right up to the antenna, the LED tuner, pitch correction, as well as the larger target plate antennas, has resulted in my not having to pay anything beyond casual / very infrequent attention as how I'm addressing the pitch antenna.
So, while I'm quite excited to see where you might take the physical portion, I'm concerned that you won't get the full "experience" (for whatever that's worth) before changing things too much (I truly wish you could spend a month with my prototype). I realize that playing styles are quite personal, and I hope you don't think I'm strong-arming you to change yours. But I would urge you to at least have some configuration of what you end up with be roughly on par with the ergonomics of the prototype, just to give them a fair shake.
"2) We discussed earlier the viability of providing a fixed output for VCA processing into a pitch preview output (with analog conditioning). Can I assume that this would not in any way change a board layout, since this would be an FPGA change only, to re-purpose the second SPDIF converter channel (or another)? The VCA pitch-preview processing would be on a separate board."
I don't have plans at the moment to generate stereo, so yes there is a second channel available. It would be a software change, the FPGA logic is already stereo. And I bet we can do that processing in software to your satisfaction (he says to a perfectionist! :-).
"3) This may be more effort that it is worth, but if you could make good use of the 8th LCD menu space that is currently dedicated to the MAIN return on all pages, it might be nice to have dedicated central hardware button to take care of this function no matter where you are. Preferably a large, green button similar to those used as panic buttons on test equipment. I'll admit that part of this is driven by the fact that I have a large number of illuminated green push buttons leftover from my CNC mill project, but don't let that influence your opinion on this..."
Encoder 7 (the 8th encoder) and the LCD position (lower right) that corresponds to it is the UI page selector. You can see an older version of the UI it in action here (preset load and store was the main page back then): [LINK]. You can't see my hand, but I'm rotating encoder 7 to flip between UI pages. The main page is the first page, and there's a hard stop at the first and last pages, so a simple counter clockwise quick twist of encoder 7 gets you back to the main page. You won't need a button, but maybe you could use it for something else, like auto-calibration. I used to use one of the encoder pushbuttons to do auto-cal, but twisting an encoder is much easier.
"4) So for the front panel I'm planning on including the 8 encoders, LCD display, dimmer pot, power switch, maybe a couple mini jacks, and some future PP control holes. And the big green button, which is going on anyway just because I want it -I could just duplicate the encoder 8 push button function for now.
For the back there would be a phone jack audio output, maybe a duplicate or line level PP output, power adapter jack, and maybe panel mount USBs for the programmer and UART. Any other suggestions?"
I'm powering via the UART USB cable. If you want to power another way you'll need a ground somehow. You might also put resistors on the UART leads to keep them from back-powering the FPGA if you power some other way. My genuine Altera programmer also has idiotic / dangerous power cycle issues: if the programmer is powered down (USB disconnected) with the FPGA powered then the FPGA backpowers the programmer, which pulls a huge load and can damage things. Your programmer is different and so may not have these issues. I don't think you'll use the programmer very often at all, so just having access to the programming header on the FPGA board should be sufficient. I stuck my programmer inside for ease of development, but rarely use it at this point and will at some point remove it.
"5) If it works out that I can have the FPGA eval board plug onto a main board without cabling, do you have recommendations on any unused pins that should be brought out to accessible solder pads for future expansion, or any that I can be certain will not be used so that board space is not wasted?"
If it doesn't hurt to pull unused pins out to pads then I would do that. If that's too painful, then pull out however many are easy for you. Internal pin assignment is a quite flexible resource inside the FPGA. There are a few pins that have more dedicated global resources, like the PLL clock inputs. And the pins tend to be paired for LVDS if you want to use that (I'm not in this design).
Did you grab my FPGA pin spreadsheet? [LINK]? It shows what pins and their types are brought out to the board headers. No clock pins are on the headers, and I've avoided using pins 3, 7, 10, and 11 because they go to the 4 LEDs on the board (which could be desoldered to allow their use), and also avoided pin 125 which is the FPGA reset. If it's not clear, the FPGA board provides +3.3V to the rest of the system via the header pins, and the 5V pins are inputs or outputs depending on how you're powering the board (outputs if you use an external adapter plugged into the barrel connector on the board, inputs otherwise).
"6) Finally, I know you don't like to get pinned down on this, but I may want to have a little fun with the logo on my ugly prototype. Is it dLev, dLEV, d-Lev or something else? How about the "Wallin" (small print, upper left) "d____" (large print) "Digital Theremin" (medium print, under the name)? Nothing will be set in stone, unless I make the housing using some of my leftover granite tiles..."
Ha ha! Let's go with D-Lev (and maybe no "Wallin" - it's just not very sexy sounding).
