Updated 20 May 2019

Following on from my work on a friend’s Aerophone, I’ve built a midiBeam- based transmitter module for my EWI-USB. It looks like this:

Inside the grey box is a midiBeam2 transmitter (TX01) and a Hobbytronics Mini USB Host. The black box on top is a 5600mAh powerbank. Both items are Velcro-ed to the EWI.

I’ve previously used a Yamaha UD-BT01 low energy Bluetooth unit for transmitting the MIDI commands to my synth, but BTLE theoretically adds a minimum of 7.5msec, and about 10msec in practice, and the total latency with my new synth was too much. The midiBeam (MB) claims 0.38msec latency, which is negligible.

Surgery Required

The MB unit comes only in a DIN plug version, and the EWI doesn’t have a DIN socket, only a USB, so I had to fit in a USB MIDI host and remove the DIN plug from the MB. I wanted to power the USB host, the MB and the EWI from the one battery, so I removed the MB circuit board from its box and packaged both units in a 3-D printed enclosure like this:

From the left are: the midiBeam trasmitter, the 1000uF capacitor, the LM2936 3.3V regulator and the Hobbytronics host. I hard-wired all the connections so I could keep it as compact as possible (no internal plugs).

The circuit diagram looks like this:

The previous work done on the Aerophone midiBeam module showed that the MB needed a capacitor on the 3.3V supply because of the high in-rush current on start-up, so I incorporated that.

Result

The unit performed faultlessly. There’s no noticeable latency difference to having a cable connection. The draw on the battery is about 120mA at idle, about 150mA when in use, and the battery lasts for about 10 hours. The unit is light and compact.

Success!