i2c2midi
i2c2midi is a simple DIY 3 hp eurorack module that speaks I2C and MIDI. It's primarily build to be used together with monome Teletype. It receives I2C messages from Teletype and converts them to either MIDI notes or MIDI CC messages to control external devices like synths and effects.
Currently in prototype status: The first prototype was built using a horizontal protoboard and a LEGO 2x16 plate as front panel.
Collaboration is welcomed: Ideas, recommendations, tips and help for improvement are greatly appreciated.
Table of content
Specs
Usage
About the firmware
Schematic
Protoboard layout
Powering it from a Eurorack bus board
Repository content
Thanks
Details
- DIY eurorack module (prototype)
- 3 hp (LEGO front panel)
- Inputs: I2C 3 pin
- Outputs: MIDI TRS (Type A)
- Based on Teensy 3.2
Todo: Create a PCB and proper front panel.
Usage
After connecting the module to Teletype via I2C, use the following code in a Teletype script:
Send MIDI notes
EX 2
EX.M.CH channel
EX.M.N note velocity
Send MIDI CCs
EX 2
EX.M.CH channel
EX.M.N controller value
Note off messages
The firmware takes care of Note off messages automatically, but is currently monophonic per channel. Note off messages are sent when a new Note on message arrives or after 500 ms.
Todo: Make the note duration of 500 ms editable via I2C as well. Todo: Make it handle polyphony.
About the firmware
As of now, the firmware is written specifically for I2C messages sent from monome Teletype using the disting Ex MIDI OPs by scanner-darkly. The i2c2midi module “poses” as a second disting. Based on that setup, there are a few things to note and hardcoded within the firmware:
-
The following addresses are specifically reserved for the disting EX within the Teletype firmware:
0x41,0x42,0x43,0x44(65, 66, 67, 68). Since the module should act like a second disting EX, it is set up to listen to I2C messages on address0x42(66). This could be changed to act as the first (65), third (67) or fourth (68) disting EX instead. -
The I2C messages for the disting Ex are constructed as
<address> <command> <optional bytes according to command>. See here or here for further details. -
The “send MIDI message” command of the disting Ex is
0x4F(79) and is constructed as<address> 0x4F <status> <optional data byte 0> <optional data byte 1>. -
<status>refers to the MIDI status. MIDI note on messages have the status 144-159 for channels 1-16. MIDI CC messages have the status 176-191 for channels 1-16. -
Sending a MIDI note on (e.g. note 48, velocity 127, channel 1) therefore looks like this:
0x42 0x4F 144 48 127. -
Sending a MIDI CC (e.g. controller 1, value 60, channel 1) therefore looks like this:
0x42 0x4F 176 1 60.
The firmware uses the i2c_t3 Library for reading I2C and Arduino MIDI library for sending MIDI.
Schematic
Protoboard layout
BOM:
- Teensy 3.2
- 2 x 2.2kΩ Resistor (R1, R2)
- 2 x 47Ω Resistor (R3, R4)
- 2 x 5 generic female header pins (or proper 10 pin shrouded header)
- 2 x 3 generic female header pins
- 1 x Green Thonkiconn Stereo 3.5mm Audio Jack (PJ366ST) (Note: graphic shows different jack)
The following graphic shows the Protoboard with (right) and without components (left). Note the deliberately broken connections on the board:
Powering it from a Eurorack bus board
As of now, I went with a dirty hack to power the module directly from a Eurorack case. Please be warned – this is NOT a good solution and one should proceed with absolute caution and at their own risk!
In order to access +5V from the bus board and to power the Teensy via its VIN pin (5V-6V tolerant), I use a standard eurorack 16 to 10 pin power cable – with the 16 pin jack plugged to the bus board UPSIDE DOWN. Again, please be careful when messing with Eurorack power.
Todo: Use a 7805 5V regulator to use standard +12V from the bus board.
Standard Eurorack
REVERSED (!!!) to access +5V
Repository content
firmware— The Teensy/Arduino code that converts I2C messages to MIDI out messages.hardware— Everything hardware related- Schematic
- Protoboard layout (with and without components)
- Fritzing file
- Illustration regarding the power cabling (!)
pictures— Some pictures of the first working prototype.
Thanks
Thanks to scanner-darkly for developing the disting EX Teletype OPs and helping out on several occasions during the making of this module.