I’ve finally finished the MIDI USB pedal that I mentioned I was prototyping a while ago. I’ve put some build details here along with source code http://www.cutlasses.co.uk/cutlasses/?p=149 . It’s fully programmable and has an LED which flashes in time to the MIDI clock. I’m really impressed with TEENSY as a platform. So easy to get started with minimal electronics experience. Next up I want to have a go at making some TEENSY based Eurorack stuff. Starting with a simple 12-bit digital delay. Does anyone here have any experience of similar projects? I thought there’d be loads of people doing it, but I haven’t found that many. I’ve just got myself a Radio Music DIY kit (my first Eurorack module). https://www.thonk.co.uk/shop/radio-music-full-diy-kit/ Hopefully building this will set me in good stead to design and build my own.
The Neutron Sound Orgone Accumulator is a Teensy-based oscillator.
I’ve got a few small projects kicking around on them - nothing worth sharing yet, but one might become moderately meaty. It helps particularly that the Teensy 3 has a single pin DAC on it - but you might also want to investigate external DACs, possibly in the form of the Teensy Audio Board.
Ah, that looks interesting.
Is the reason you suggest investigating other DACs because the converters in the Teensy don’t sound very good? I think I remember @tehn saying something similar? My plan is to implement something on the standard Teensy, then if I actually finish it I’ll get a Teensy Audio Board to improve the resolution and potentially have better converters. I’d be interested to see what you are working on @infovore when you are ready to show something off!
Other DACs just in case you want more than one channel of it, or higher bitrate.
The Teensy 3.1/3.2 has a single pin of 12-bit DAC. This is what the Radio Music uses for its mono audio out. You might want higher quality outputs, or more of them, hence looking at other DAC chips. The Teensy Audio board, for instance, has a two-channel 16-bit DAC on it.
You can approximate analogue output using PWM from a digital pin, but it’s revolting and I wouldn’t recommend it at all.
“Something to show off” feels a way off - and when I do, it’s going to be a thing for manipulating triggers (and specifically, clock) rather than audio-rate CV.
Oh I see, thanks for the explanation. Well, mono should be fine for my initial experiments. Looks like pin A14 from the schematic…
Yep, it’s that single odd pin on the bottom row.
I bought a few to build with a while back, but that was almost a year ago now and nothing much done at all 
http://bleeplabs.com/ has some (non-eurorack) Teensy projects, which I think are open sourced (Delaydelus, Thingamagoop 3000 (?))
Besides RM and NeutronSound, I’ve also built this: https://github.com/mxmxmx/O_C/tree/asr
(There’s more Teensy projects in that repo).
MacroMachines Omni I think is basically a Teensy. But I’m not sure it’ll be open-sourced.
Bastl seems to have something in the works (Take a look at their github). Difficult to tell what though.
If you don’t mind gcc/JTAG, the NUCLEO-F303K8 seems like a nice/cheap alternative. 3 DAC channels and it’s a M4F. I think (never tried), there’s a libMaple (=quasi Arduino IDE) port.
Just put together a video of my latest DIY project. Again it’s Teensy based. This time in the Eurorack format, making use of the Teensy Audio Shield. It essentially samples small sections of live audio and lets you manipulate them. https://www.youtube.com/watch?v=Wnd8HAyvk2A
this is great! you might want to consider moving power regulation onto the board - and also some reverse polarity protection…
(I got the boards for the prototype of the thing I mentioned waaay earlier in this thread back last week. first notes from the 0.1 code: it’s really fun. can’t wait to share more).
aha - here’s a grab of what I’m currently working on:
which came back from fab last week. Amazingly, it basically is already working in simple form, and now the real job is overhauling the firmware. I imagine it won’t be a Teensy forever: the code is mainly math and logic, so I think this is going to be an ATMega directly on the board, which will be a new adventure for me. Still. My first time sandwiching two boards and it all working OK.
Cheers! I wanted to keep the circuit relatively simple as it was the first time getting a pcb fabricated, so left out any power regulation etc. It’s just connected directly to the 5v line on the Eurorack power. Seems to work for my prototype needs. I might add it to the next version of the pcb, along with more jacks for CV input, although the Teensy Audio shield hogs a lot of the analogue inputs.
Will you be putting up more details of your project soon? Looks great!!
eventually! I kinda want to have something like a 1.0, though, because the thing it’s doing is both relatively straightforward and yet… somewhat unique? I’d rather just go “here is a thing, it is done” than get a bit held up. It’s intended to ultimately be a DIY project, I think.
Good luck with your second version - more than happy to offer input/a hand. I reckon you can get several HP off that PCB if you’d like to, easily - there’s bags of space - and that’s before you put in power reg/protection. Although 5V from 12V is as simple as a regulator and a capacitor, pretty much.
More importantly, though, like I said, loving the sound and functionality as it stands.
Yeah, I could definitely do a more compact version of the PCB. I was just learning Eagle at time, man, that software has a steep learning curve! Cheers for the offer of help.
yeah, EAGLE is… challenging. Having spent ages wrapping my head around it, I’ve developed a kind of Stockholm Syndrome - I’m actually rather attached to it now, and have got quite fast to the point it’s usually quite enjoyable. I describe routing as a really, really compulsive puzzle game, to people who can’t see the charm. I still learn new things in it every day, though - always trading tips with other DIYers…
As you’ve probably found, though, the easiest way to learn it is to have a friend to teach or answer questions - the documentation online is all quite spare.
Question for the Teensy experts.
I want to build this to interface Max + Euro. Is it possible to make modifications to the code to get more than just two CC/pitch outputs? Just duplicate the code given for A21/22? My ideal would be 8 outputs from which I can send CC from Max as CV to Euro.
A21 and A22 are the only analog pins on the teensy 3.6 that go through a DAC so I think if you need more than that you’d need to add some more circuitry. I don’t know enough to help with what that would look like though.
yep, this is correct. If you want more analog outputs, you’re going to have to start adding more DAC chips to the circuit. DAC chips go up in price based on precision (number of bits of input) and number of outputs. For instance, the quad DAC in an Ornament and Crime is about $12 for the chip alone. The extra circuitry to address such things is not hugely complex, but it’s not really a beginner project.