EuroRack 6HP MCU Experimenter Module PCB Build Guide

By Kevin on December 15, 2024

Here are the build notes for my EuroRack 6HP MCU Experimenter Module.

Warning! I strongly recommend using old or second hand equipment for your experiments. I am not responsible for any damage to expensive instruments!

If you are new to Electronics, see the Getting Started pages.

Bill of Materials

EuroRack Control IO PCB (GitHub link below).
EuroRack Control MCU PCB (GitHub link below).
EuroRack 6HP Panel PCB (GitHub link below).
Arduino Nano or Raspberry Pi Pico.
Either 2x 15 way headers (Nano) or 2x 20 way headers (Pico) - PH5 headers recommended.
2x 14-way header pins and socket - PH5/9.5mm headers recommended (see below).
Header pins.
1x 1N5817 Schottky Diode.
1x 10Ω resistor.
1x 47uF electrolytic capacitor.
1x 2x8 way shrouded pin header socket (EuroRack power).
M2 mounting posts, screws, nuts as required.
Jumper/connecting wires.

Power supply circuit (Pico only):

L7805 regulator.
1x 1N5817 Schottky Diode.
1x 47uF electrolytic capacitor.
1x 100nF ceramic capacitor.

Note the above are the minimal set of components required before actually building in specific circuits.

A note on headers. I'm using "PH5 short profile" headers which don't stick out as much as normal headers. I'm matching these with 9.5mm long header pins. The difference can hopefully be seen below.

Note: there are "PH3.5" headers too, which need 7.5mm long pins, but I've stuck with the PH5.

Some typical components required for the actual circuit modules are as follows. The quantity and values will vary according to the actual circuit built of course.

BAT43 Schottky diodes.
MCP6232 OpAmp and (optional) 8-pin DIP socket (for PWM audio output).
2N3904 NPN general purpose transistors (for Gate/Trigger IN).
Resistors - various.
Ceramic capacitors - various.
Electrolytic capacitors - various.
Potentiometers, jacks, switches, etc. - as required.

Build Steps

Taking a typical "low to high" soldering approach, this is the suggested order of assembly for the MCU board:

Resistor and diode(s).
Regulator (if used).
Capacitors.
Microcontroller headers.
Eurorack power header.
PCB connecting headers.

The order of assembly for the IO board will depend on the components and circuit being built, but it is recommended that the connecting headers are soldered on before any connections are made from the rest of the board to the header.

This is the general suggested order of assembly for the IO board.

All diodes.
All resistors.
DIP socket.
- Note: one of the capacitors has to be fitted within the footprint of the DIP socket. This is probably easier to do on the rear of the board and possibly prior to fixing the DIP socket.
Disc capacitors.
Transistors or regulator.
Pin headers.
Electrolytic capacitors.
PCB connecting headers.
Inter-circuit connecting links (if not using headers).

Be sure to check the components are being soldered to the correct side of the boards. Most of the components (apart from the connecting headers) for the MCU board are on the rear. Most of the components (apart from the connecting headers) for the IO board are on the top side.

Any controls (potentiometers, switches, jacks, and so on) will have to be fixed to the header connections on the IO PCB. It is possible to use header pins and jumper wires, but a better result will probably result from using directly soldered connections. YMMV...

If using my EuroRack panels, then there are GND and VCC rails that can be used to make adding IO controls easier, but these will need to be connected to the power rails of the IO PCB at some point too.

Here are some build photos for the Raspberry Pi MCU board.

Here are some build photos for the Arduino Nano board.

Here is the build photo for the IO board.

Generally, although it might be a little tricky to solder around the header, it is still advisable to solder the headers on before making the final intra-board links.

This is because it is highly likely that some of the patch cables will need to pass over the solder-side of the headers.

Alternatively it might be possible to make the intra-pcb links on the underside of the board, meaning all soldering can be performed "from the top". In this case, it might be advisable to put the headers on first...

Testing

I recommend performing the general tests described here: PCBs.

It is strongly recommended that all unused EuroRack power connections are checked and verified that they are unconnected to each other, +12V and GND.

Then it is really down to checking the power supply is working and all of the MCU IO is correctly present on the IO board once both boards are connected.

It is strongly recommended that the board is tested on its own, completely independently of any other modules or an expensive EuroRack power supply. In fact, it is NOT recommended that these boards are used with any other modules or an expensive EuroRack power supply at all. They are designed for use with cheap, DIY systems only.

PCB Errata

There are the following issues with this PCB:

Nothing at present.

Enhancements:

I could probably switch the position of the central mounting hole and shuffle some of C500, C550, C600, or C650 which would then probably allow for a companion mounting hole on the MCU board, where this is currently some spare space on the PCB.
I thought to add some headers for power on the MCU board, but it might have been useful to include two headers - one on each side of the board - to allow simple jumpering across from one board to another, to save on the cabling requirements of every board being connected back into a EuroRack system and to pass on the 5V connection if required.
I should have some panels produced with mounting holes in the right place to fit these PCBs directly.
Alternatively a third PCB could be produced with mounting headers to connect to the audio, INPUT and OUTPUT headers of the IO board to support the mounting of pots, jacks and switches.

Find the IO and MCU PCBs on GitHub here.

Find the blank panel designs on GitHub here.