MidiREX -- DIY MIDI loop sequencer


@austingreen – do you still have that power supply?


Any idea about what type of glue would manage to keep those pesky buttons to stay in place?


Herma 1251 photo glue


I use acrylic glue. It holds them well enough but you can pop them off if you need to


I didn’t need glue. I just used a pair of long nosed pliers to squeeze together the two little plastic bits inside the cap VERY GENTLY and the caps clip on perfectly


@gabby I had the idiocy of mixing my MIDIBud buttons with the MIDIRex ones and now I have a mix of buttons that have plastic bits and buttons that don’t.

Thanks for the suggestions gentlemen, I’ll try something other than the Pattex Repair Gel. :slight_smile:


@kvitekp - yeah but I have a lot of them pluggd in at once so I can’t be 100% sure but I think the first one only put out 200ma and the second one is 500ma. The switch was mainly coincidental due to moving stuff around, the ever evolving setup.


not sure, if i should post this over at the midialf forum because the place is quite abandoned so here i go:

i build the midirex some time ago as did a friend of mine. we sourced the parts / flashed the atmegas together.

we both have some strange issues:

  • after power off/on the memory seems to get partially corrupted.
  • the device freezes from time to time (controlls won’t work)
  • the device stops to send/recieve midi notes from time to time, but the controlls still work.
  • it skips some notes when recording occassionally
  • it seems to me midi notes that are send thru (not recorded) get the note off message removed (stuck notes), but i haven’t tested that a lot.
    -otherwise it works. (it’s usable as long as the power is not removed and none of the glitches happen)

i suspect that due to the fact, we both have the same issue, it’s the same problem and most likely not a soldering issue, but related to sourcing (wrong memory ic??) or programming (wrong fuses?)

i finally wanted to troubleshoot the issue and tryed to programm my midirex again today.
atmel studio won’t work for me. (never verify right when flashing) i think it’s because of my chinese avrmspmkII clone not working correctly with atmel studio. (which is fine with avrdude - i did ambika,midialf,various diy with it all fine)

so i used:
avrdude -B 100 -V -p m644p -c avrispmkII -P com8 -e -u -U efuse:w:0xfd:m -U hfuse:w:0xd6:m -U lfuse:w:0xff:m -U lock:w:0x2f:m
avrdude -B 100 -V -p m644p -c avrispmkII -P COM8 -e -u -U flash:w:muboot.hex:i -U flash:w:midirex.hex:i

unfortunately i still have the same issues.

i am kind of lost with this one.
does anybody have any ideas what to try next?

i roughly followed this thread and i can’t remember anybody having problems like this.


Does it have tap tempo by any chance ?


Yes, MidiREX does have tap tempo feature.


Rereading the manual I came up with a couple of ideas as feature requests:

1) a) Per Track Transposition. A “round robin” functionality would allow for consecutive incoming MIDI notes to transpose each track separately from the rest. First note transposes track 1, second note transposes track 2, etc. One other possibility is to do this only when a notes are held: first incoming note always transposes track 1.; if first note is held then second incoming note transposes track 2, etc.

b) One other, simpler method of doing per track transposition would be to “plainly” allow a root note per track instead of per part, in a similar fashion like it is done on the current (1.94) firmware. This could give interesting results, although method a) allows the user to create his/her own chord progressions in a hands-on fashion. Using the root note method b) allows for fixed intervals but still gives a bit of flexibility as choosing weird roots for each track would wield interesting results.

2) In MIDI Rx channel, would it be possible to have each track receive on a different channel? If all are set to the same channel then the functionality resembles the current one, so it doesn’t stray far from what we have but it opens up the door to creative territory. :slight_smile:

By the way, I successfully managed to upgrade the firmware and I’m very happy with the additional functionalities. Thanks a ton kvitekp for your most excellent work! You’ve got me day dreaming of a nice setup around the MidiREX.


@loderbast, I have the same issues with my midiRex…
There is a thread on avrfreaks, about fuses and serial communication :

Not sure, but it might be worth checking.


@loderbast – somehow i missed your posting, sorry about that. I’ve built half a dozen of MidiREX’es for friends and myself and have never experienced anything like that. Have you tried to change power supply? Did you verify fuse settings? Are you sure second SRAM IC is not inserted into the spare socket?


had both ics installed…
thanks. works like a charm now!


Arghh… you’re not the first one! I’ve added a (hopefully clear) notice to the MidiREX building instructions. I’ll also check to see if the firmware can at least initialize that second SRAM IC to prevent it from sending garbage to the bus.


maybe add a comment on the bom, too. i think the mistake happens when sourcing - if one is left with an extra memory ic and an empty socket after building everything, it is quite likely they stick it in there.
it says Quantity:1, but Part: IC1, IC2 in the bom.
i think thats where i got the idea to get two.

great machine by the way. i am very much enjoing it and i am happy i didn’t really screw something up :slight_smile:


OK, BOM entry updated. Glad you like it :wink:


Glad you could solve your issue @loderbast
Damn, i feel lonely now :wink:
i’ve tested again : mine skip notes off and on messages, occasionally, … it seems to happen only in slave mode …
no 2nd sram ic in mine, and i have tested 3 power supply, without success…
I swapped the 6n137 with another one, just in case… no luck
Any clue ?


@zardoz – try to run it on internal clock and see if the problem persists.


@zardoz: thanks. i am confident you will get it working, too.