MIDI Over UART with Arduino and CircuitPython

As I began to hack the Scout Synth, I went down a MIDI over UART rabbit hole adventure with CircuitPython and Arduino.

#midi #arduino #circuitpython

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[BlitzCityDIY]

hi hello hey there- a lot of comments about what the problem is communicating with the Scout directly with UART from another MCU. if you watch until the end, you'll see that there is not a problem to solve because it's working and i address that both devices need to be on the same shared power and ground connections in order for UART comms to work directly.

i didn't think about this when i first started down this rabbit hole, since as i pointed out the feather and qt py worked without issue since they were both getting power from the same USB ports on my laptop and honestly i haven't worked too much with devices communicating via UART directly. i figured other folks starting out also wouldn't think about this which is why i went through everything step by step to demonstrate the troubleshooting and to illustrate it plainly. i also have circuit diagrams in the github repo showing this as a reference.

[MattGT]

Is it possible you are missing a ground connection? Try adding a ground wire between the QT Py and the Scout. I see the QT Py RP2040 has jumper wires to the + & - rails of the protoboard, but I am not seeing anything except the UART wire on the Feather or the Scout. That would explain issues on battery, or working for a limited time as the ground voltages float away. If so, it is an easy fix. You already did all the hard stuff!

Thanks for sharing this, and all of your projects. I also enjoyed seeing it on the Adafruit Show and Tell, and look forward to your future MIDI endeavors!

[genghisbunny]

Excellent, thanks for sharing, I'm so glad to have discovered your channel!

[crusherjones]

I am stoked for this video, this build, your work, that cat pic, and that SMOKIN' Sonic Youth Pettibon poster.

[JohnSandlin-ej]

Those Opto-Isolators were to prevent ground loops between different synths.

[SimpleDIYElectroMusicProjects]

I'm enjoying watching what you're doing with your Scout! It's great to see MIDI on them. I can confirm you can actually drive quite a lot of Arduinos from a single UART line off the back of a MIDI interface - in my case, I'm driving around 10 or more as part of my Lo-Fi Orchestra! I'm not sure that technically this is something one should be doing, but for a multi-drop receive only, I figured I'd be ok, and for my purposes it is.

Is the QtPy a 3V3 device? Have you had to put some level shifting in there somewhere? Could something like that be related to the power issues you were seeing?

I've also found that even if things are powered differently, it can often be useful to ensure they are sharing a common ground, especially when linked up over a comms link like this. Real MIDI doesn't care, as it has optoisolators, but when linking directly to UARTs, the devices need to have a common reference point to know what the baseline for a high or low signal is. Sometimes a single jumper wire connecting GND pins might do it.

Thanks for posting. I look forward to seeing where you take it next.

Kevin

[Davedarko]

Sounds like a voltage issue? I remember hearing / seeing it in the datasheet that the atmega328 is only capable to run at 16MHz at 5V and it seems like the low voltage made it go out of sync. Also not sure if the ftdi likes voltage signals that low when it's comparing the 4V battery signals to the 5V coming from USB - that midi circuit seems to work as a levelshifter here.

[captain]

Lady, can you tell me, is it possible to run a Leonardo as a MIDI controller without connecting to a PC, just by powering it externally? I have a switchboard with 8 switches and 1 exp. pedal and I use it to send CC messages to PC and use it to toggle on and off vst instruments and effects. I also want to use this for my guitar processor (Boss GT-10) that accepts MIDI signals as an extension of controls, and want to connect with a MIDI cable to it. Is this possible ? I can share my current code if necessary.

[tedysamsi]

Ho to make serial uart on orange Pi as MIDI device working