Narwhal

Midi Out not driving X0XB0X Midi In

11 posts in this topic

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.

Share this post


Link to post
Share on other sites

Hello,
Did you put 220 Ohm or 47 Ohm on the outputs lines? R21/R22 and R26/R27

Best Bruno

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
17 minutes ago, Phatline said:

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.
 

4 hours ago, Narwhal said:

Is this a known situation?

Yes you're not alone, the problem is not the Core but xoxbox design.
https://forums.adafruit.com/viewtopic.php?f=12&t=82849

Edited by Antichambre

Share this post


Link to post
Share on other sites

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.

I'll give that a try today.

Share this post


Link to post
Share on other sites

MIDI is actually a current loop, not really anything to do with voltages. 

Share this post


Link to post
Share on other sites

Yep the Spec states that  :cheers:

5bad0fce9d3b8_ScreenShot2018-09-27at9.49

Edited by Narwhal

Share this post


Link to post
Share on other sites
36 minutes ago, latigid on said:

MIDI is actually a current loop, not really anything to do with voltages. 

Totally right this is just an led.

@Narwhal
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.

http://ucapps.de/mbhp_midi_io.html

Put the 47 Ohm it will work, don't take care about MIDI specs, there's no beads here.

 

Edited by Antichambre

Share this post


Link to post
Share on other sites

I haven't extended the IO with MIDI-IO boards yet.  Thanks for the reminder on the need to adapt them as well when they arrive.

I've always been called a stubborn Swede, so I put in 33? and 10?.  The outputs works perfectly now with the X0X's.

Share this post


Link to post
Share on other sites

Yah that what I fixed... this things is a beast.  I've had much fun today.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now