 Adafruit_TrellisSet trellis(&T[0], &T[1], &T[2], &T[3]);
 const uint8_t       addr[] = { 0x70, 0x71, 0x72, 0x73 };
 
-boolean       grid[8][8];                  // Sequencer state
+uint8_t       grid[8];                     // Sequencer state
 uint8_t       heart        = 0,            // Heartbeat LED counter
               col          = 0;            // Current column
 unsigned int  bpm          = 240;          // Tempo

    if(++col > 7) col = 0;
    // Turn on new column
    line(col, true);
    for(uint8_t row=0; row<8; row++) {
      if(grid[col][row]) {
        usbMIDI.sendNoteOn(pgm_read_byte(&note[row]), 127,
          pgm_read_byte(&channel[row]));
      }

  if((t - prevBeatTime) >= beatInterval) { // Next beat?
    // Turn off old column
    line(col, false);
    mask = pgm_read_byte(&bitmask[col]);
    for(uint8_t row=0; row<8; row++) {
      if(grid[row] & mask) {
        usbMIDI.sendNoteOff(pgm_read_byte(&note[row]), 127,
          pgm_read_byte(&channel[row]));
      }
