Update 24th of May 2024: I've made a new version of the frontpanel which looks a lot neater!

Update 27th of January 2024: I found a hardware issue with respect to the MIDI IO (luckily before I shipped any), that's why I retired the product so suddenly. In the mean time I solved the culprit and made a new hardware revision which means that it's back in stock (with a lower price)! Also check out the new documentation link I added; I made a number of firmwares with demonstration videos :)

What is it?

The Toepler (named after a German scientist) is a digital module for 3U Eurorack systems, positioned as a software development platform. The core of the module consists of a Atmega32u4 and is compatible with Arduino and the well-known Mozzi Library. The size is 14 HP. Overview of connections:

• 1x USB Type B (for USB MIDI and flashing firmware)
• 1x MIDI TRS In
• 1x MIDI TRS Out / Thru (selectable from firmware)
• 3x Button (one of which is a reset)
• 4x LEDs (1x Power, 3x PWM Controllable)
• 2x Trigger In
• 1x Trigger Out
• 4x CV In (3 of which have an scale and offset, 4th can also be used as audio in)
• 1x Audio Out (14-bit Dual PWM, DC-coupled)

A schematic and example code can be found under Documentation. The frontplate is made from aluminum. The SMD components are already soldered onto the board but you have to source and assemble the through-hole components yourselves in case you select the 'Kit' option:

• 8x Thonkiconn mono jacks
• 2x Thonkiconn Stereo jack
• 3x pushbuttons with at least 15mm shaft
• 3x 100kOhm potentiometer
• 3x 10kOhm potentiometer
• 6x 3mm LED (color of choice)
• 1x USB-B KUSBVX-BS1N-B fromKycon
• 1x 2x3 pinheader (for flashing the bootloader)
• 1x 2x7 pinheader (for eurorack power supply)

Why did you make it?

Initially I made this module for myself. I wanted a development platform with which I could experiment with various Arduino libraries and use them in a broad context and also interface. I am quite happy with the end result and made a few more than I need myself, so I'm looking to sell these to cover some of the development costs. If there is enough interest, I have designed it such that I can do more production runs easily.

What makes it special?

The broad range of connectivity allows it to be used as a swiss army knife in a wide range of situations. MIDI and Mozzi also allow the module to be truly polyphonic. The most obvious use case is a digital VCO but audio effects such as a Wavefolder, Clipper, Chorus or Pitch Shifter are also possible.

The user can tailor the firmware to his/her own needs and the possibilities are endless. The fact that the reset button and USB-B are accessible from the frontpanel allows for easy development of new firmwares.