Dual channel MIDI Interrupter


This is my take on Gao Guangyan’s MIDI2 interrupter. It features the MIDI2 interrupter board, an Adafruit PowerBoost 1000C LiPo battery management module and 5V boost converter, USB charging, a 1S 1200C LiPo, and a custom 555-based “burst mode” add-on board.

The burst mode board is a simple astable 555 oscillator with independent on and off time, and two ranges, a high and a low. This provides bursts from 1/s up to the same rate as the interrupter itself, providing for some interresting audio effects. The 555 OUT pin simply drives a trio of 2N3904’s, two of which enable or disable each channel of the interrupter, and the third drives an LED. Burst mode is disabled by flipping a switch, which disconnects the OUT pin and pulls the bases of the transistors up to Vcc.

The on-board 5V regulator of the MIDI2 board is bypassed to feed 5V into it directly from the PowerBoost module.

The PowerBoost was modified to provide remote mounting of the low-battery, charging, and done LEDs.

Finally, as a brute-force fix for transients on Vcc causing the ATMega microntrollers to lock up or reset when running in burst mode, a 1000uF electrolytic cap was mounted directly to the burst mode board. This also smoothed the ripple from the boost converter to <50mV.

All of this was crammed into a small aluminum box, which was then powder coated black.