Simple step sequencer for playing Volca Drums on a Grid via Norns

2025-04-06

I’ve had a 256 Monome Grid for a few years and version of the Norns called Fates that I use to control it. I also built a 8x8 Monome Grid called an Arduinome before that. I have a Volca Drum which is a drum simulator synthesiser which can make all kinds of crazy sounds. I wanted to use these instruments together.

I love the large size of the 256 for Step Sequencers, you can see all the instrument channels at once down the Y axis (and the 256 could show 16 channels!), and 16 steps on the X axis. The current step position is shown by a line from top to bottom that moves left to right. You select instruments, e.g. bass drum or clap, on rows and the step to play them on the columns. Since you can see everything thats happening at once, it’s really easy to make and change rhythms while it’s playing.

There are a lot of step sequencers for Norns and the Grid and I’ve tried a bunch over the years. But I thought i’d try to build one myself. I’d only tried to make a sort of Conway’s Game of Life midi trigger script inspired by 100 Rabbits’ Orca but didn’t get very far.

Norns scripts are written in Lua which is a scripting language that’s used in a lot of game engines to do simple scripting things. One difference with most other languages is that array indexes start at 1 instead of 0, this is meant to be initiative for non-programmers to get started with but it trips me up a lot! One issue I had with my step sequencer was that there was a little gap of time after the sequence restarted, I wasn’t sure what it was until I remembered the index 1.

I started off by going through the Norns tutorials and the basis for the step sequencer is Grid Tutorial 9 which talks about how to draw to the grid. These tutorials are great and cover a lot of what you can do with Norns. I added a clock and drew the position line on the Grid and also mirrored that on the Norns screen itself. I wanted to keep the Grid just for the sequencer with no controls on the grid apart from setting step trigger positions and only displaying the triggers and the position line. This way I can use all 256 buttons for the sequencer and have the Norns screen and controls for any other utilities.

function update()
  g:all(0)

  for x = 1, gridSize.width do
    for y = 1, gridSize.height do

      if (beatColumn == x) or (beatColumn ~= x and grid[x][y] == true) then
        g:led(x, y, focus.brightness)
      end
    end
  end

  g:refresh()
  redraw()
end

The update loop for drawing to the Grid.

Next was to send the midi signals, I am using a cheap USB to 5pin midi adapter that I connect to the Norns. When you setup Midi you specify the OS Device, in this case there was one Midi device, my USB adapter, on port 1 (remember index starts at 1). Then you send the note on (and then off) with the command :note_on(note, velocity, channel), so I tried note 0 (midi index starts at 0), velocity 127 and channel 10. I could see that the midi messages were being sent to the USB adapter because the light was flashing, but the Volca Drum wasn’t doing anything.

After a little research on how the Volca Mdi works I found out that first you have to set the Midi mode by holding down the record button when you turn it on. And then send Midi to a separate channel for each instrument (and starting at index 1!). The Volca Drum has 6 instruments that can be triggered by the buttons on the device or by Midi. When sending Midi to trigger the first instrument you send an “on” message with the key being anything, I used 100, a velocity, I used 127, and on channel 1. For the second instrument I send the same but on channel 2 and so on. There may be a way to have this all sent on channel 10 with an update to the firmware.

Next I wanted to use one of the Norns buttons to play and pause. I used button 2 (sometimes called KEY2) to update a bool.

function key(id,state)
  if id == 2 and state == 1 then
    play = not play
    print("play: ", play)
  elseif id == 3 and state == 1 then
    -- nothing
  end
end

-- ...

function update()
  g:all(0)

  for x = 1, gridSize.width do
    for y = 1, gridSize.height do
      if (beatColumn == x) then
        
        if (play == true) and (grid[x][y] == true) then
          -- Selected position is on the line, play the note.
          key = 100
          velocity = 127
          channel = y
          out_midi:note_on(key, velocity, channel)
          out_midi:note_off(key, velocity, channel)
        end
        -- Draw the line.
        g:led(x, y, focus.brightness)
      end
      
      -- Draw selected positions if they are not on the line.
      if (beatColumn ~= x and grid[x][y] == true) then
        g:led(x, y, focus.brightness)
      end
      
      
    end
  end
  
  g:refresh()
  redraw()
end

The updated update code with sending the Midi on and off right afterwards as well as play/pause.

Finally I wanted to use one of the rotary encoder knobs to change the BPM. This works at the Norns OS level and is referred to as “tempo”. I originally thought it would be the clock.sync() function but that is to do with how many steps per beat. You can fetch the current tempo with clock.get_tempo(), but to change the tempo you pass the delta from the encoder to params:delta("clock_tempo", delta). It’s also possible to set the tempo directly with params:set("clock_tempo", 100) but when I tried this with keeping a local copy of the tempo the updates were slow, updating the delta directly is much faster when turning the encoder.

Here is the script working, this is an older version without the play/pause and bpm on the Norns but you can set the triggers and it plays through the Volca! If you have a Volca Drum and a 256 Grid and want to try it out, or if you want to take the code and change it for your set up, it’s hosted on github.