Ok, I have my Zynaptik board now… I am not likely to hook up the midi ports externally, but I just had a thought… I could try and use them internally as an input … am i right in thinking i can wire from an ESP32/ESP82866/Arduino directly as follows? :-
gnd
5V - via a 220 ohm resistor
signal - via a 220 ohm resistor
like this …
https://www.arduino.cc/en/tutorial/midi
but without the socket?
I’m keeping well out of this. I’ve dished out enough bad advice on Opto Isolators to not even dare to comment, but yes MIDI can do nasty outragous things like that, but don’t esxpect ANYONE to play with you or provide you with a MIDI station clock 
I believe so. Check out Alph45tar’s https://github.com/alf45tar/PedalinoMini. There’s a simple schematic in the Readme that’s essentially done the same way.
Could you elaborate a bit more?
I got confused between the 8 & 6 pin opto isolators on this thread Where to edit wiring for a minimal Zynthian. I’d assumed the 6N138 & the H11L1 were equivalents.