The current implementation supports 4 pushbuttons and 1 toggle switch (usually bank switcher) and a hard-coded range of MIDI sequences. Hardware i s based on a single ATtiny2313 microprocessor.

Original design intended to retrofit an analog Vox VFS5 footswitch to control an Axe-Fx II effect processor by Fractal Audio Systems. However the housing might be custom made as well or fit into any other pushbutton-based device.

Hardware Specs

Hardware is designed to work with a power supply of 7 to 25V DC which is suitable for a standard 9V DC power supply or battery which is common for effect pedals.

The logic is powered by a Atmel/Microchip ATtiny2313 processor, which can be swapped with about any AVR controller providing 8 I/O ports and a USART interface. MIDI signal is directly connected to the USART output (active low) of the controller and the 5V DC supply of the board through two 220 Ohm resistors.

Pin on Controller	Pin on MIDI Jack	Function
X5.1	2	Ground
X5.2	5	Signal through 220 Ohm
X5.3	4	+5V through 220 Ohm

The provided layout is perfboard compatible with a more or less minimal layout to fit into the footswitch casing without removing the original PCB.

Footswitch Layout and transmitted MIDI codes

Label	BANK	CH1	CH2	CH3	CH4 (Tuner)
LED	⭕ (1 green, 2 red)	-	-	-	-
Button	⭗	⭗	⭗	⭗	⭗
MIDI Codes	Bank 1: 0xB0 0x00 0x00 0xC0 0x00 Bank 2: 0xB0 0x00 0x01 0xC0 0x00	0xC0 0x00	0xC0 0x01	0xC0 0x02	0xB0 0x0F 0x7F

As documented, the CH4 Button does not enable Channel 4 as expected, but sets the effect processor into tuner mode (which bypasses the output, so implicit mute). Thus you effectively control 3 channels on each bank 1 and bank 2.

The LED is green for Bank 1 and red for Bank 2. When in tuner mode the LED flashes in the current color with a frequency of about 2 Hz.

Final Example

Below two pictures of the final prototype implementation handsoldered on a perfboard. Placed inside a VFS5 next to the original parts.

License

The project is licensed under GPL v3 license.