I finally have my MBSeq working (yay!) and I’ve been learning a lot about how to use. But today I decided to switch it up and go from playing my Waldorf Microwave XT to driving a X0xb0x. But what should have been just a simple swap of cables has turned out to be a strange situation. It appears that the Midi output ports on the MBHP_CORE_LPC17 are unable to drive the midi inputs on either of the two x0xb0x’s that I have. If I take the sequencer output and run it into an emagic interface into the computer then route it back out another output, then the x0xb0x’s begin to play.
Is this a known situation? Will it work any better if I use a CORE_STM32 boards in the MBSeq? I’m guessing right now that this is an electrical situation with the either the LPC17 or the x0xbox boards, but I haven’t dug any deeper than discovering the situation yet.
lpccore gives 3.3v on midi while stm32+midio gives 5v so xoxbox have problems with this non standard low voltage - try the stm core.
normally if you put 47 Ohm resistance instead of 220, all optocoupler will work correctly. the 4N37 also. Even if I think this optocoupler is not the best for midi app. but this seems not to be the issue.
Thanks for all the input everyone! My lpc board was built when the board was first release, then I hadn’t looked for any corrections until now. I definitely have 220 Ohm resistors in there.
I haven’t run into anything else that I have that can’t signal the x0x. It appears to only be an issue with data coming from the lpccore. This is also confirmed by looking at the MIDI Electrical Spec which specifically mentions the problems with 3.3v signaling and details the different resistor values as a solution.
MIDI is actually a current loop, not really anything to do with voltages.
Totally right this is just an led.
TK does mention of it on the MIDI-IO Page from ucapps(bottom of the page)
Quote
Board Modification for 3.3V based MIDI outputs
If you are planning to use this module for a microcontroller which outputs MIDI OUT at 3.3V level (such as the MBHP_CORE_LPC17 module), please change the R3, R5, R8 and R10 resistor values to 47 Ohm, and connect J1:Vd to 3.3V instead of 5V!
This measure is not required for microcontrollers which output 5V, or where MIDI output (Tx) pins can be configured in open drain mode.
