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Mimir's Well

This repository contains everything you need to build the Mimir's Well guitar pedal.


  • arduino: code for the display driver, and for writing the "yellow" EEPROMs
  • assembly: documents to help people building from a kit or PCB
  • eeprom-helper: simple tool to help when creating EEPROMs. see its README
  • pcb: gerber and dxf files, e.g. if you want to produce your own PCB
  • schematics: schematics
  • v1: a one-off prototype (which is now my most-used pedal)

Writing EEPROMs

The pedal has 2 pairs of 24LC32A EEPROMs. Each pair contains a bank of 8 programs, and has a "Yellow" EEPROM and a "Blue" EEPROM. The colors aren't significant, and just refer to the color I use when writing each chip's number on it. It's a simple way to avoid getting them mixed up.

There are lots of ways to write to EEPROMs, and this is only one of them.


This holds the program name and control labels for each program in the bank. I use this EEPROM Helper script to make the label text file, or the arduino file.

Using an EEPROM programmer:

You can write to it using these shell scripts: and

Using an arduino:

You can also write it using an Arduino sketch. You can hook it up as follows:

connecting EEPROM to Arduino for writing


This holds the FV-1 programs.

You may be be able to write the banks using an arduino and a custom sketch, but I simply use a very inexpensive EEPROM programmer. Specifically I use a USB CH341 EEPROM programmer. These can be found for about $5. You may need to find and install USB drivers.

I use the ch341eeprom commandline tool on Mac OS X to write the data to the USB programmer. If you're not on Mac you'll need to find an alternative tool.

To create these banks I do the following:

  1. Create a "hex" bank using SpinAsm assembler
    1. Unfortunately this only runs on Windows. An alternate assembler exists but I haven't tried it.
  2. Convert it to a "bin" file using the srec_cat util from the "srecord" package
    1. brew install srecord on Mac
    2. srec_cat bank-input.hex -Intel -o bank-output.bin -binary
  3. Erase the EEPROM, probably optional
    1. ch341eeprom -v -s 24c32 -e
  4. Write the bin file
    1. ch341eeprom -v -s 24c32 -w bank-output.bin
  5. Check for problems. Optional but recommended
    1. ch341eeprom -v -s 24c32 -r /tmp/eeprom.bin # read back the data
    2. diff /tmp/eeprom.bin bank-output.bin # this should not output anything

Here is a script I use for steps 2-5.

"EEPROM Helper" tool

To help streamline this process I have a really simple tool I use: eeprom helper

It's just a simple javascript page that lets me check which programs I'll be burning, then it does 2 things:

  1. Gives a snippet of arduino code or a text list of labels for the burning the Yellow chip, described above.
  2. Lists the spn files for reference, which is helpful when manually working with SpinAsm Assembler in step 1 while burning the Blue chip.