I want to send midi between two boards and since it's both microcontrollers I thought I could do this without the optocopuler part.
So I just hook up in to the out or do I need a resistor inbetween?
Midi between boards
mongrol
#2
I do this between a Teensy and Axoloti using RX/TX UART ports. No resistors or optocoupers needed since it's just plain old serial. I'm a cowboy though so perhaps I'm doing it wrong. 
If the annotation in your image is correct, you need a pullup resistor (anything in the range of 3k3-22k) on both data lines to make the open collector circuit work.
Google "open collector" if you want to know why.
valmir
#5
Keep us updated please, that something that I'll surely want to do in my future multi axos setup!
Same thing here, I'm planning a two axoloti system controlled by a QuNexus and a QuNeo.
As the axolodi does not support hubs, i plan to connect the QuNexus and QuNeo to each axoloti.
They will share the MIDI USB information through the MIDI din.
Surely the multi axoloti SPI x3 communication will be a great feature, a game changer. But i guess that it is not easy to develop and debug with all the stuff that needs to be synch'ed to avoid glitches...
Blindsmyth
#7
Midi via the pins works great so far, but I'm also looking forward to the spi solution.
I think another way to approach this is to use something like an Arduino (which does support usb hubs) as a router...
e.g. Arduino <-> usb hub <-> axo 1... axo N
the usb hub, the Arduino could then be programmed to take messages from various axo boards and forward them to others. (depending upon the topology you want).
I like this approach as its flexible, usb is fast, and also can power the axo boards off the hub (also the Arduino too).
I'm doing something similar with a BeagleBoneBlack/Bela, but overkill for just this. its not bad, whats quite nice, is to program the axos, all I need to do is unplug the usb host from the BBB, plug it into the computer, and I now have all axos connected to the computer for programming.
valmir
#9
Nice! Surely I'll remove some dust from my long forgotten Pi and try it when I get my 2nd (and 3rd) axo!
Any suggestion for a gui-less program to do this on Raspbian? Pi will be the host and forward usb controllers messages to the axos... I guess...
Blindsmyth
#10
@logsol is kind of doing that with the c.h.i.p, have a look here
The Idea is nice because you can create a more star shaped data flow.
The only thing I'm a bit unsure is how to create user interfaces with several layers of buttons and leds. Would you do that on several axoloti boards in paralel or do that on the pi/chip/arduino and spit out different cc/notes for different shift layers...