2026-01-18 17:32:13 Agh... I keep thinking of so many little simple systems I'd like to put together. Latest one is a MIDI controller stomp box to go with my electric guitar looper pedal (and who knows, later on maybe try to get the looper functionality into my box as well, but that would be quite a lot more involved). I really, really need to get with and just get a Forth done for a Cortex M4, pick a chip, and get 2026-01-18 17:32:15 the generic circuitry (power, etc.) done once and for all so I have a launchpad for such projects. 2026-01-18 17:32:37 I mean, the HARDWARE for a MIDI stomp box is like next to nothing. Likely like $30-$40, tops. 2026-01-18 17:33:28 On the other hand, if you want a good quality eight-pedal MIDI stomp box off the commercial market you can easily pay $700-$800 for it. 2026-01-18 17:33:50 And all it does is send well-timed commands over a 5 mA current loop. 2026-01-18 17:34:18 And offer some LCD screen menu system for configuring what you want your buttons to do. 2026-01-18 17:40:53 The looper functionality, though... that would involve ADC and DAC ooperation, signal processing, buffering that audio in and out data in RAM while flowing it back and forth to/from a much larger flash-based backing store, etc. I mean, my particular pedal can store up to 13 hours of stereo audio, at a fidelity level suitable for musical performance. That's a lot of storage - you're not holding 2026-01-18 17:40:55 that in RAM. 2026-01-18 17:42:20 The ARM chip I looked at yesterday has three 12-bit ADCs that can do five million sample a second, but will do hardware handled oversampling that gets you the equivalent of 16 bits. I THINK that would be enough, provided all of my internal processing was 32-bits so that I didn't lose any of those 16 bits due to round-off. 2026-01-18 17:42:52 But I'm not 100% sure I could really get there with the on-board peripherals - it might be necessary to add more performant ADCs and DACs to rerally make it work well. 2026-01-18 17:43:45 Anyway, that wouldn't be an immediate goal. I'd start just with the eight buttons. The looper pedal itself basically is a "one button" thing - it is a PEDAL. But that really only gets you a limited amount of on-the-fly control. 2026-01-18 17:44:37 Things become enormously more flexible if you connect "several" buttons to that can do other things like shift your around memory tracks and so on. 2026-01-18 17:45:19 You can do all that stuff with the pedal alone, but not on the fly while you play - you have to reach down and turn a knob or push a panel button or whatever. 2026-01-18 18:47:38 KipIngram, onboard ADC's and DAc's seem quite noisy to me 2026-01-18 20:06:31 Yeah, I saw some chatter to that effect in some low intensity noodling I did. It's a shame - that kind of integration is so awfully nice. 2026-01-18 20:07:10 I would kind of question the wisdom in even having specs that high if they're not truly usable. 16-bit A/D is no good if there are 4-5 bits of noise. 2026-01-18 20:07:50 Obviously the chip can't do anything about outside noise, but you'd think they could at least promise not to ADD excessive noise. 2026-01-18 20:09:25 Anyway, what really drew my attention to it was how easy it would be to implement the MIDI and stomp buttons - at least that doesn't have any such issues. 2026-01-18 20:09:43 Then I just started to eye the rest of the peripheral list and get greedy. 2026-01-18 20:53:48 KipIngram, it may be that no one who tests these on-chip ADC's actually understands ADC working requirements and impliments them properly ? 2026-01-18 20:54:57 for instance the mcu ADC's dont include the required low impedance amplifier to drive the ADC input capacitor etc ? 2026-01-18 20:56:12 just that amp alone is a hard thing to impliment given the needs of low voltage accuracy and bandwidth, most op-amps are very noisy in my experience 2026-01-18 20:57:54 Ive had to make op-amps out of discrete BJT's in the past to obtain low noise audio microphone amps, to boost the signal up to levels where theyre high enough to be used 2026-01-18 20:59:41 KipIngram, this was for crystal microphones inside the specialised tooling that watchmakers used to hold mechanical watches when they were working on them and setting their timekeeping accuracy 2026-01-18 21:00:57 KipIngram, Ive never done any 'audio' electronics, I was pretty much specialised in, industrial, instrumentation,automotive and embedded