flounder was conceived as a small, low-cost, diy “friend of norns" which runs on a Teensy 4.0.

It can be used as a midi controller and a standalone synth with stereo output. It was inspired by pangrus’ multi and other Teensy-based diy midi controllers like andrew’s bleached.

The schematic, BOM and gerber files are on my Github, so anyone with DIY skills can make one. It uses the same form factor as my roundabout synth, so it’s cheap to get PCBs made.

I’ve written a few programs for flounder, although I’m admittedly not a great programmer.

This is a basic midi controller with 12 MIDI-mappable knobs, a full-octave touch MIDI keyboard and octave control (using the 6 “function” buttons). This should work with anything that supports MIDI over USB. I used andrew’s code from bleached for the basis of this.

blipo_v2 / blipo_2018
The most fun thing I’ve done with flounder so far is use the 12 pots to make a digital version of Rob Hordijk’s Blippoo Box. This is a different implementation than the Supercollider/Norns one. I made this using the Teensy Audio Library and created a few custom objects along the way to make it work. Since the Blippoo Box hardware came in different iterations, I made different programs for the “v2” and “2018” versions. Disclaimer: I don’t own a Blippoo Box so am I making no claims this is an exact emulation. I did reference the Leonardo Music Journal article, Rob’s lectures/videos and many other video demos to make sure it has the right vibe.

A polysynth with an ADSR, oscmix, filter with LFO, ensemble chorus, and reverb.

A single mono oscillator and ADSR envelope, to demonstrate how the touch keyboard works. This can be a basis for a more complicated synth. It also works as a midi controller.

After soldering the PCB, this helps verify that everything is working properly by sending knob/key values to the serial monitor.

While this first version accomplishes what I was going for, there’s room for improvement.

  • At the moment, Teensy 4.0 is out of stock (along with pretty much all the Teensy models). :frowning:
    Edit: Looks like Adafruit has some Teensy 4.0 boards in stock.

  • The SMD headers on this are pretty hard to solder. See my Github page for more info on that.

  • When hitting the “black” keys on the keyboard, it’s easy to accidentally hit one of the neighboring keys, because of the way the keys extend up.

  • The last key on the keyboard (which is tied to pin 13 on the Teensy) is connected to the Teensy on-board LED, which makes it not ideal for touch. I’ve compensated for it in code, so it works fine, but if I do a rev, I’ll rethink this.

  • The touchplates are mostly on or off as far as touch sensitivity. I might look into doing pads like the Make Noise Pressure Points to enable more modulation capabilities. Of course the TeleTouch keyboard is a better option for someone looking for that.

I’d love to hear any questions, comments or feedback. If you build one, please reach out with any issues.


This looks great and the blipo sounds great :slight_smile: Horribly tempted to try and build one

Edit: if anyone in the UK is ordering pcbs for this I’d be glad to chip in and get one :slight_smile:

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Thanks for the interest Cementimental!

Here’s a test of the basic polyphonic synth I wrote for it called “pitta”. I’m not much of a programmer or keyboard player, so did my best in both haha. :slight_smile:


I’m having fun writing some more programs for this. Here’s a relabi drum machine I’m working on:


I just discovered this project. Excellent work!
Sounds great, I’m very tempted to build one.


Finally got mine built up and tested out!! Thanks so much again to @mattkuebrich !


Sounds awesome! Will definitely consider building one!


i really like this patch – it is not on github…
can you give more details about it? :slight_smile:

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Thanks! I’ll try to post the code to Github soon… it’s really fun to play with. It’s based on ideas from John Berndt’s essay on relabi. I also checked out the manual for the ADDAC Systems “VC Relabi Generator” module. Then sorta freestyled my own ideas into it.

The basic idea is that 3 sine wave LFOs that are mixed to create a rhythmic but non-repeating “relabi wave”. You can set different thresholds in that wave to trigger the different drum samples. And each of the LFOs can modulate each other. Reverb and distortion are added to the output for fun. Right now it just uses 909 drum samples.

I do have plans to keep working on the code and implement some different methods to approach the “self-erasing pulse”. Something shift-register based ala the rungler is an obvious choice.


oh my. :smiley:
hehe very excited for that!

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