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 schematic! C1 0.1uF
Also refer to the TurboCPU Installation instructions for more guidance.