If you are in the UK or EU (ouch), here is a source for a DIY MIDI IN/OUT/THRU bare PCB that can be used with the TurboCPU. No DAC option, but otherwise it’s pretty similar to the MTG MIDI board. Two wires need to be flipped and a couple parts I substituted with my preferred values, but it’s the only viable TTL-to-MIDI board I’ve seen anywhere that sticks to the spec just like the MTG one does. All the Arduino one’s I’ve seen suck.
Here is the bare board:
Here is the schematic:
Here it is connected to a test setup on my bench:
Power (red) and ground (black) go “straight through”, but the Tx/Rx data lines need to be crossed (yellow, blue). I also changed a few components. Here is the parts list I used:
R1, R2 470R Make sure to use high efficiency LEDs R3 4k7 R4 - Not used, leave empty R5 to R9 220R IC1 74LS14 IC2 6N137 Different IC than the schematic! C1 0.1uF
Also refer to the TurboCPU Installation instructions for more guidance such as wiring the jacks.