44 thoughts on “MidiREX DIY Resources

  1. Hi!
    I almost finished building your awesome MidiRex!
    But i have a question about flashing the Atmega:
    Do i need this muboot.hex or do i just have to use the midirex.hex?
    Can i flash it with my USBasp Programmer and do i have take account of something?
    Thanks a lot for your help!

    Best regards

    • You only need to flash bootloader (muboot.hex) if you plan to update firmware via MIDI.

      Any AVR programmer will do. Just make sure you set the fuses correctly.

  2. After i had looked into the !doit.cmd batch file,
    i maybe found the fuses:
    high fuse = D6
    low fuse = FF
    extendet fuse = FD
    Are this the correct ones?

  3. i was looking into enclosure options, ice blue or clear hammond acrylic like this one seems cool: http://www.hammondmfg.com/pdf/1591D.pdf but of course the board is just a little too large for that… pete, could you please tell me if it is possible to cut 3,5 to 4mm on top and bottom of the board to make it fit? from the layout i would think it is uncritical. also i generally trust case mounted connectors more than pcb mount ones, so that could go. is there a need for a power switch or is it ok for the unit just to pull the psu plug? and one more: say if i chain 4 units by midi thru on the units themselves, would there be a noticeable lag between all merged notes on the output of the last unit? or is it adviceable to split the input and merge them all with external gear?

    • Yeah, you can probably shave off a few mm from top and bottom of the board. Power switch is not critical at all, just a convenience. You install trial version of Eagle and check exact measurements of your case against minimized.

      MidiREX has “software MIDI THRU”, which means MIDI events are decoded then encoder before being passed thru, so delays add up. If the delays are acceptable or not depends on your application. Generally, you don’t want to have more than one THRU.

  4. i built it now with the case from ponoko. really a well designed unit, but i somehow miss an internal click. i see all the i/o pins are all fully used… it would be really cool to add a flat piezo to an output pin and glue to inside the case and have an acoustic click that way. i always liked the precise internal click on the mmt8 – i often sequence several monophonic synths, so adding another module just for the midi click (+ setting it up) is always an annoyance. maybe there is a possibility to add this instead of one midi led and merge the two midi leds to “midi activity” with a future update, would also be a great option to trigger external analog gear.

    • Nice idea! I’ve never played with piezo buzzers and am not familiar with their electric requirements, however if they could be driven from the MCU pin, i could probably add an option to use a pin to output a beep or a click.

      • i did a little research, most people attach them directly to the i/o pin, for current limiting possibly 500R can be useful. depending on specific type, they can play frequencies from 0.5-100kHz and start resonating (noticeable louder) from 1 to 5kHz, possibly depends on diameter. maybe a typical 880Hz 5mS click created with PWM could be sufficient, or even an emphasized tone on every first step of the cycle. i just had this idea as common speakers are a bit large (had the mmt8 speaker in mind), a piezo glued to a plastic case can become quite loud and has the game&watch appeal. on the other hand, todays technology speakers from mobile phones and laptops are powerful and small aswell. i hooked the pulse output from midigal/midiclk to a small amplifier once and it was also sufficient as an audible click (thinking of the double use as click/trigger without the need for a click frequency option in the midirex menu). either way, this video shows how piezos with a small enclosure can sound, i am not sure if resonances come from the enclosure or the disc itself: https://www.youtube.com/watch?v=ADe89-w3JIA

  5. Hi,

    I’ve decided to build this thing. In the BOM it’s stated that IC2 should be omitted. The Eagle files do include IC2. What should I do? Can I delete IC2 and associated components (R4 and R5) from the schematic and PCB?

    Thanks, cheers!

    • Current firmware does not use the second SRAM IC, so MidiREX will work if you omit it and the related components. However, future releases of the firmware may use the extended memory, so i recommend leaving the socket and resistors in,

      • Thank you very much, I appreciate your quick answer! I won’t trash them then.

        What’s up with the much requested MIDI overdub recording feature btw? Is it possible at all? Is it likely that it would be implemented in the future?

  6. midi overdub feature? you mean merge two tracks? that would be a thing. HECK, i would start a kickstarter even to get some of my wish features… but it seemed i pulled too much nerves from master pete already 😉

  7. Hi, I have just built the midirex, and from what I can tell it works with my piano keyboard! I haven’t worked out all the features yet… But here is my problem…. I am not a keyboard player, I use a guitar synthesiser with midi in and out.. But I am just getting squeaks and pops with it on the recorded track! I know the gr20 Roland sends a lot of data, like pitch bend for each string.. Actually I think it’s like six keyboards in one where each string is treated quite independently … Do you think I’ll ever get this working? Or should I focus on a audio looper…?

      • Ok, so I have set the synth to poly mode, as the mono mode sends each string on a seperate midi chanel… so now the synth is working similar to a keyboard, with all notes on one chanel and only one pitch bend signal. and it works as such!
        But there is a second problem, because unlike a keyboard where pitch bend is a seperate wheel or knob, the guitar synth is sending continuous bend signal as the strings bend the notes as you play. This is great because it makes it sound very natural. however it is causing the recorded track to follow the new notes and pitch bend, so as I play and bend notes the recorded sequence is changing key! quite and interesting effect…. but a bit confusing…
        I tried plugging the output of the Midirex into another Keyboard sound module, and It appears to work ok… (I am not 100% sure yet as its a piano only with no pitch bend) is there any way to ignore pitch bend on the Midirex?

      • MidiREX by itself cannot filter out PitchBend events as they are essential for voice pitch definition. You’ll need some external device to do pitch bend filtering.

  8. Hi, this looks like an amazing project!
    It would be my very first one though, so may I ask you a couple of questions?
    Is it possible to use footswitches instead of the tactile switches?
    I’d like to turn midirex into a pedalboard .Generally speaking, what you can do with your foot can also be done with your hands, if you just put the thing on your desk, but the opposite is not true! I’d like to have free hands, especially for selecting tracks. Therefore, I need more than two footswitches, and there’s no reason why I should buy an estrernal midi pedalboard IF i can turn this into an actual pedalboard!
    Would it require different diodes or different parts and schematics whatsoever? Or is it just a matter of substituting tactile swittches with the standard guitar-pedal-style switches? (Of course, I woudl put it in a wider enclosure, with cables leading to the 4 track switches, select, rec and run. Only the screen, encoder and LEDs would be “visible” in my board, with the remaining switches aligned below at a certain distance)

    • MidiREX track selection involves double key action when you press SHIFT key and TRK key. Doing this with one foot is problematic. MidiREX MIDI interface has direct track selection CC which could be assigned to the pedal.

  9. Hi, is there a swing / shuffle implementation? Would be great if you could quantize with swing. A global swing setting would also be interesting.

  10. Hi, I finished to build mine and I’d like to start the enclosure.
    Do you have dxf or svg files for the front panel ?
    Thank you


  11. Hi,
    I just received my MidiRex and i’m loving it so far ! It would be nice to be able to tinker with the source code but the zip file on this page is outdated (v093). Is there a place where you can find the source code for the last version of the firmware ?
    Thanks !

  12. After playing around with the Rex for a while I’m very happy! However, I can’t seem to get the metronome feature to work. When I select the note I can hear it play, but when trying to record I hear nothing. I’ve tried it with a drum machine and a synth and have the same issue with both. I assume it’s something simple that I am forgetting, so any insight would be much appreciated.

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