This little board adds MIDI in and out via 3.5mm (1/8“) TRS connectors, along with an expression pedal input. It's all simply connected to the pi-Stomp Core board with a 5 conductor ribbon cable.
TRS connectors were chosen because they have a much smaller footprint, are easier to plug/unplug and seem to be the future of serial MIDI.
You can use simple TRS to DIN adapter cables for connecting to equipment with the classic 5-pin DIN connectors.
Just make sure they are listed as “Type A” which have the more common connection scheme than “Type B”. You can also build your own.
This should be a very straight forward build. One could likely assemble without instructions, but it's still a good idea to view the photos and assemble in the approximate order shown. At least note that the Diode and IC are polarized.
|R1-R4||220 Ohm Resistors (1/6W 3mm)|
|R5||33 Ohm Resistor (1/6W 3mm)|
|D2||1N4148 Diode (there is no D1)|
|MIn||3.5mm (1/8”) TRS Jack|
|MOut||3.5mm (1/8“) TRS Jack|
|Exp||6.3mm (1/4”) TRS Jack|
|S1||8-pin DIP Socket|
|U1||6N137 or 6N138 OptoIsolator|
The diode footprint is wider so bend the legs a few mm from the diode body
It's polarized. The Black band on the diode should correspond to the band on the board silkscreen.
Since the connections to the pi-Stomp board are by a male header, you'll typically want to connect it with female jumpers. You could install a male header onto the MIDI board then attach with female-female headers, or use a jumper cut to the length you desire and solder that to the MIDI board.
Installed into a 1590J enclosure. For mounting the Expression jack, it's generally best to have one washer on the inside, one on the outside along with the beveled washer and threaded shank.
“-”, “+”, Rx, Tx are connected to the equivalent pins on the pi-Stomp board and “Exp” to Analog input 7.
For the Expression pedal, an “adc_input” definition should be added to the “analog_controllers” section of ~/data/config/default_config.yml. Feel free to chose another midi_CC msg number (0 trhu 127)
analog_controllers: - adc_input: 7 midi_CC: 77 type: EXPRESSION