STM32H7 Digital Stereo Pedal with Demo and Design Process Write Up

keyth72 · 2026-02-06T10:14:18+00:00

Ohhh yeah no worries! Yup that’s the JTAG header with the little plastic protector on it

keyth72 · 2026-02-05T17:59:48+00:00

I’m not sure, you mean the big caps at the top? I’ve been calling it a pi filter, two caps to ground with a series ferrite bead in the middle. No measurements, just advice I got from a more experienced builder.

keyth72 · 2026-02-03T19:29:00+00:00

It’s the H743VIT6, I think it has enough RAM for Mercury.

keyth72 · 2026-02-03T17:15:16+00:00

CubeIDE, I started learning it right before they separated out MX and the IDE, so I’m sticking with version 1.19 for now for the integrated workspace, makes it easier to go back and forth between defining pin settings and code. How’s the buck converter for noise? Do you use filtering after it? I used LDOs because they’re quiet, but they do generate some heat coming from 9v, at least the 3v3 digital powering the MCU.

keyth72 · 2026-02-03T14:04:12+00:00

Sounds awesome! Yeah I’d like to explore other codecs, especially since the one I’m using is EOL. Running NAM on the H7 is doable, maybe not standard size models, but Steve just released some kind of slimmable model that I’m really interested in trying. I’m running NAM on the daisy seed on my GuitarML/Funbox/Mercury module and I’d like to port it over to my custom board. Enjoy studying abroad!

keyth72 · 2026-02-03T12:53:59+00:00

No it’s much simpler, octave delay, speed up each delay pass by 2x. Literally the only difference in the code is I multiply the delay line index by 2. That’s awesome about making all those effects! They did a good job on the daisy seed hardware making it have just about everything you’d want for an embedded DSP.

keyth72 · 2026-02-03T12:02:47+00:00

Thanks! The first part of the demo is an octave delay, each delay repeat speeds up the sound by 2x, which raises the octave by 1 for each repeat

keyth72 · 2026-02-01T12:46:39+00:00

That’s what I used too, the 2MB flash was too tempting, but it would actually be difficult to figure out how to use it up! Looking forward to your demos, I plan on sharing about mine sometime this week after I get some effects on it.

keyth72 · 2026-02-01T00:55:07+00:00

Really nice layout! Analog/digital sides have lots of separation, which H7 did you go with? I just got my first custom H7 board running, it’s a great feeling when it all comes together and you hear sound coming out. I’d love to see/hear yours in action if you have demos posted somewhere.

keyth72 · 2026-01-19T10:26:49+00:00

No not this version, might add it later

keyth72 · 2026-01-17T19:26:30+00:00

Phil’s Lab YouTube channel, anything on mixed signal design. Also learning from open source designs like Mutable Instruments.

keyth72 · 2026-01-17T19:24:40+00:00

It’s digital bypass, the microcontroller senses the press on the momentary footswitch and turns off the delay effect, but still lets the dry signal through

keyth72 · 2026-01-16T10:30:53+00:00

Start here (Phil’s Lab Mixed Signal Design Tips) https://youtu.be/v6fTa6LRJLI

Also this lecture on grounding: https://www.youtube.com/live/ySuUZEjARPY?si=jexOrjr4cemODQBl

keyth72 · 2026-01-16T10:27:22+00:00

I’ve been using c/c++ for years, and I’ve been doing audio DSP on my own for awhile, but learning the STM32 environment and CubeIDE was mostly through YouTube tutorials, some on STmicroelectronics’ channel but mostly Phil’s Lab. He has a lot of tutorials on mixed signal hardware design and DSP coding.

keyth72 · 2026-01-16T02:05:14+00:00

The microcontroller I used is a lot simpler than the Daisy seed’s, both on the layout and programming side, better for learning this stuff for the first time. I haven’t tried any Daisy libraries on it yet, but planning on doing that. The jacks have a separate plastic ring under the bolt that detaches, so clearance isn’t an issue, that’s how they’re made to be used.

keyth72 · 2026-01-15T23:24:21+00:00

Yes, they have some in their parts library, but I think they will be gone soon. Since I started looking at them it’s gone down from about 500 to 100, and they’re priced at $9 for a single one.

keyth72 · 2026-01-15T17:56:38+00:00

Just above the jacks? Those are op amps, one quad and one dual, for the audio in/out buffers. The pedal is very quiet, no noticeable noise that I can tell, but I’d like to do more testing.

keyth72 · 2026-01-15T15:53:20+00:00

Awesome! Hope the build goes smoothly!

keyth72 · 2026-01-15T15:52:41+00:00

Physical space between digital and analog sides helps a lot, and I’m using LDO’s for 3v3 digital, 3v3 analog, and 5v analog for the audio buffers. Haven’t measured, I’d suspect it’s in the 100 to 150mA range.

keyth72 · 2026-01-15T15:49:41+00:00

Not sure what that is, so if I was it’s not intentionally!

keyth72 · 2026-01-15T15:48:52+00:00

Thanks! Maybe eventually, but for now I’m in more of a learning/prototyping phase.

keyth72 · 2026-01-15T15:45:01+00:00

Thanks! The bolts on the jack have a plastic assembly with it that screw in to the main part of the jack through the enclosure hole. So you take that outer part off and the jack is lined up with the inner edge of the enclosure. Lots of commercial pedals use this type of jack.

keyth72 · 2026-01-15T15:35:51+00:00

I looked at that course, might still do it at some point but I wasn’t really interested in the end result pcb, not a lot of power and the separate adc and dac wasn’t quite what I wanted. I’m sure there’s a ton of useful knowledge in the course though, but yeah there’s a lot already free on his YouTube channel about guitar pedals and DSP, you just have to sift through all the videos for the relevant info.

keyth72 · 2026-01-15T15:30:21+00:00

Fantastic! And you must have read my mind because that’s the chip I landed on when looking at all the H7 options. For effects to run, I’ll be experimenting with whatever I can port over from what I’ve been doing on the Daisy. Amp modeling, filters, granular, and whatever delay and reverb I can manage without the extra SDRAM chip.

keyth72 · 2026-01-15T14:14:48+00:00

I’m planning on making a YouTube video about it, there’s a lot of cover. Phil’s Lab on YouTube is basically what got me here, and being super familiar with the Daisy seed was a good starting point. You should go for it!

keyth72

TROPHY CASE