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

    { 17, 21, 25, 29, 49, 53, 57, 61 },
    { 18, 22, 26, 30, 50, 54, 58, 62 },
    { 19, 23, 27, 31, 51, 55, 59, 63 } },
  note[8]    = { 72, 71, 69, 67, 65, 64, 62, 60 },
  channel[8] = {  1,  1,  1,  1,  1,  1,  1,  1 };

void setup() {
  pinMode(LED, OUTPUT);

Adafruit_TrellisSet trellis(&T[0], &T[1], &T[2], &T[3]);
const uint8_t       addr[] = { 0x70, 0x71, 0x72, 0x73 };

uint8_t       grid[8];                     // Sequencer state
uint8_t       heart        = 0,            // Heartbeat LED counter
              col          = 0;            // Current column
unsigned int  bpm          = 240;          // Tempo
