I'm making a synthesizer, please check my work, and help out

Community Jobs and Paid Consultancy
1

I'm building an analog synthesizer with digital control from a custom Arduino board. I'm handling most of the hardware and software design, but I'm looking for an engineer to assist with various hardware and software tasks including:

  • Check work on an existing PCB that I've designed in KiCad
    • I'm offering $250 for this. It's a rather crazy analog design, four oscillators on one SMT board, about 400 total components. I messed up, and I'm literally paying for my mistakes here, because although I have a schematic for one oscillator, I unfortunately did not design this PCB directly from a schematic. So, the only way to check my work is by hand, against the schematic that I have. The only net class I have defined is ground. I just want someone to sanity check that the PCB is hooked up as the schematic is, I'm not as much looking to make large changes to the design or layout. But, I'm always open to feedback and critique, and I'm certainly no expert, as you can maybe tell by looking at my board.
  • Design custom Arduino layout and board definition using ATSAMD51J or similar chip
    • I'm happy to pay your hourly rate for this (and all other) work. I'm prototyping with an Adafruit ItsyBitsy M4, and need more pins. Unfortunately, I think I may need every pin on an ATSAMD51J, so I'm flexible and will use whatever works. This is a low-power synth running at 6V, so the regulator on the ItsyBitsy M4 is perfect. The only other things on the digital board will be two DACs that will connect to the microcontroller via I2C.
  • I need help connecting to both I2C devices simultaneously via DMA.
    • I've been using the I2C_DMAC Arduino library which has been great, but I haven't been able to get it to work with both DACs together. The problem may be that I'm also accessing the internal DACs via DMA (Adafruit_ZeroDMA library).

I'll provide detailed specifications, schematics, and business requirements as necessary for each task. I'll consider candidates with any amount of skills and experience in circuit board design and microcontroller programming. I'm by no means an expert, my degree is in design and media arts, and although I got my start in hardware on Arduino, I'd say I'm better at analog design than I am at microcontrollers at this point. I'd love your help, I have a lot else to do to finish the synth, and I'd really rather not do these specific things myself :blush:

For now, I'll leave an artsy picture of the PCB layout, of course I'll provide full KiCad files for the gig. And a pic of an early prototype of the synth.

butterfly copy
butterfly copy1920×761 363 KB

IMG_8476 copy
IMG_8476 copy1920×1440 217 KB

2

Rather than designing a custom board I'd think you'd come out ahead to use the Adafruit ItsyBitsy M4 with headers and just put sockets on your PCB for it.
How many pins do you need? It might be easier to use a board with more pins.

3

Try contacting mitxela.com on his forum mitxela.com forum or direct In case it wasn't obvious... His work is intense software - projects - mitxela.com

4

I need 51 pins, but also needs to be powered by 6V so adafruit grand central won't do unfortunately, and I'd rather not multiplex the itsybitsy. I'll be producing about 100 synths at a time so even at that small volume custom boards could be about half the price. Definitely a nice-to-have though, I could probably make it work with a stock board.

5

can you share that?

My two pennorth - if you can use readily available modules like the Adafruit ItsyBitsy M4 and integrate them into your PCB it would make development and debugging easier and your end product more maintainable.

6

sure! It's a tunable VCO where you can sweep a knob to fade between triangle, sawtooth, and pulse waves.

I appreciate the feedback about using readily available modules. Unfortunately I can't find a stock board that fits my requirements of 51 IO pins and 6V battery power input. Also, I'm not very experienced, but I assumed that in the long run at scale I could save a lot of money and time by making my own board, including having the factory flash them.

VCO copy
VCO copy1920×1222 195 KB

8

I designed and built a VCO / VCF / VCA module with a 4 decade range back in the 80's using CA3080 OTA's and one of the earliest jfet op amps - LF356. It was intended to be part of a modular analog synth but never got completed although it saw use in our acoustics lab at Rutherford college (now UNN in UK)

My suggestion was to use multiple modules and do distributed processing so the number of pins wouldnt be an issue.

That seems a very complicated board to perform what appears to be a relatively simple function. ?

9

super cool! These NE5517 OTAs I'm using are wonderful, I can't believe I can run them so well at +/-3V.

Do you mean the VCO I shared? Yeah it's certainly overdoing it, I just really wanted to be able to sweep a knob to morph between triangle, sawtooth, and pulse waves similar to a moog sub phatty. I couldn't find any schematics online that mixed between more than two sources, so I ended up just doing a bunch of op amp math to control VCAs for each wave in order to mix them across the sweep. Works great on a breadboard, so I'm hoping it will work at least as well here haha.