The MidiFoot is a USB MIDI controller with a single button. It sends hold pedal (CC#64) messages on MIDI channel 15, but with a rotating pattern of 16 values for each press and release so you can map the messages to different things. This allows it to be used as a momentary or toggle button, and even play 4, 8, or 16-note patterns. It uses an ATTiny85 to emulate a class-compliant USB MIDI device using the V-USB library, so it’s inexpensive and doesn’t need any drivers installed to work on most computers. The PID=1508 and VID=5824 have been generously provided by Objective Development. Much credit to Martin Homuth-Rosemann for developing V-USB-MIDI, on which this is based. The MidiFoot is a creation of Geek Funk Labs, where you can find a complete bill of materials, links to obtain kits/builds, etc.
The ranges of values to map for each function are shown in the list below.
- 16-step pattern (this is the full sequence): 70, 0, 100, 30, 85, 15, 115, 45, 75, 5, 105, 35, 80, 10, 110, 40
- 8-step pattern: 70-75, 0-5, 100-105, 30-35, 80-85, 10-15, 110-115, 40-45
- 4-step pattern: 70-85, 0-15, 100-115, 30-45
- Toggle switch:
- On: 70-85
- Off: 100-115
- Momentary switch:
- On: 64-127
- Off: 0-63
You will need an AVR-C environment installed to build from source. A Raspberry Pi is quite useful as a build environment, as you can compile code and flash AVRs using the SPI interface on the GPIO header. The included Makefile assumes you are doing this - modify the AVRDUDE variable if you are using a different programmer. To install the necessary tools for compiling and flashing on the Pi, enter
sudo apt install gcc-avr avr-libc avrdude
Make the following connections to program the ATTiny85:
| RPi Physical Pin | ATTiny85 |
|---|---|
| 23 (SCLK) | 7 (SCK) |
| 21 (MISO) | 6 (MISO) |
| 19 (MOSI) | 5 (MOSI) |
| 22 (GPIO25) | 1 (RESET) |
| 2 (5V) | 8 (VCC) |
| 6 (GND) | 4 (GND) |
You must also connect a 16MHz clock source (quartz oscillator) to pins 2&3 (XTAL1&2) on the ATTiny, and ground each pin through a 22pF capacitor. To compile the software, flash the chip, and set the fuses, enter
sudo make flash && sudo make fuse
You can send whatever messages you wish by modifying the code in midifoot.c and recompiling and flashing as described above. Modify the midiPkt array to change what messages are sent - the comment above the declaration explains the formatting of MIDI packets. If you change the total number of messages, update MSG_COUNT to reflect the new value.