Audio Shield, Teensy 4.1, Neotrellis and other I2C devices


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Hello. I am working on building a drum machine with my teensy 4.1. I will be using Adafruit's Neotrellis for the drum sequencer and I set it up and it all works well with the examples on the arduino IDE. I will be using the audio board so I cant use my sda and scl 0 outputs, so I need to use the Wire1 pins 16 and 17. I have used the scanner examples and my teensy is able to detect the neotrellis
this is the neotrellis connected to wire1 14:18:24.334 -> Scanning Wire1...14:18:24.363 -> Device found at address 0x2E (MCP44XX ePot)14:18:24.363 -> done

Can anyone please help me? I am not the best at programming but I do not see what else I can do.

/* This example shows a more complex LED pattern
using a NeoTrellis board.
Note that due to memory requirements this example
will not work on boards with very limited memory such
as the Adafruit Metro (with ATMega328p)
#include <Wire.h>

#include "Adafruit_NeoTrellis.h"

Adafruit_NeoTrellis trellis;

#define MAX_RIPPLES 16

#define FALLOFF_TIME 30
#define NUM_POINTS 8

#define RIPPLE_RATE .4

#define INT_PIN 10 // Change this to the pin connected to your interrupt

#define MATRIX_POINT(x,y) ((y)*4+(x))

uint32_t colors[] = {
  0xFF0000, 0x00FF00, 0x0000FF,
  0xFF00FF, 0x00FFFF, 0xFFFFFF

union color {
  struct {
    uint8_t blue:8;
    uint8_t green:8;
    uint8_t red:8;
  } bit;
  uint32_t reg;

color matrix[4][4];

struct point {
  float x;
  float y;

struct ripple {
  int8_t center;
  uint32_t t;
  color c;
  point points[NUM_POINTS];

static struct ripple ripples[MAX_RIPPLES];

//define a callback for key presses
TrellisCallback blink(keyEvent evt){

  for(int i=0; i<MAX_RIPPLES; i++){
    if(ripples[i].center == -1){
      //create a new ripple here
      ripples[i].center = evt.bit.NUM;
      ripples[i].t = 0;
      for(int j=0; j<NUM_POINTS; j++){
        ripples[i].points[j].x = NEO_TRELLIS_X(evt.bit.NUM);
        ripples[i].points[j].y = NEO_TRELLIS_Y(evt.bit.NUM);
      ripples[i].c.reg = colors[random(sizeof(colors)/sizeof(uint32_t))];
  return 0;

void setup() {

  pinMode(INT_PIN, INPUT_PULLUP); // Use INPUT_PULLUP for Teensy's internal pull-up resistor
  if(!trellis.begin(0x2E, Wire1)){
    Serial.println("could not start trellis");
    while(1) delay(1);
    Serial.println("trellis started");

  for(int i=0; i<MAX_RIPPLES; i++)
    ripples[i].center = -1;

  //activate all keys and set callbacks
  for(int i=0; i<NEO_TRELLIS_NUM_KEYS; i++){
    trellis.activateKey(i, SEESAW_KEYPAD_EDGE_RISING);
    trellis.registerCallback(i, blink);
  //do a little animation to show we're on
  for(uint16_t i=0; i<trellis.pixels.numPixels(); i++) {
    trellis.pixels.setPixelColor(i, 0x0000FF);;
  for(uint16_t i=0; i<trellis.pixels.numPixels(); i++) {
    trellis.pixels.setPixelColor(i, 0x000000);;

void processRipples(){
  for(int x=0; x<4; x++){
    for(int y=0; y<4; y++)
      matrix[x][y].reg = 0;

  bool update = false;
  for(int i=0; i<MAX_RIPPLES; i++){
    if(ripples[i].center > -1){
      update = true;

      //push all points out from the center
      point *p = ripples[i].points;

      p[0].x += RIPPLE_RATE;
      p[1].x += RIPPLE_RATE/2;
      p[1].y += RIPPLE_RATE/2;

      p[2].y += RIPPLE_RATE;

      p[3].x -= RIPPLE_RATE/2;
      p[3].y += RIPPLE_RATE/2;

      p[4].x -= RIPPLE_RATE;

      p[5].x -= RIPPLE_RATE/2;
      p[5].y -= RIPPLE_RATE/2;

      p[6].y -= RIPPLE_RATE;

      p[7].x += RIPPLE_RATE/2;
      p[7].y -= RIPPLE_RATE/2;

      for(int j=0; j<NUM_POINTS; j++){
        int x = round(p[j].x);
        int y = round(p[j].y);
        if(x < 4 && x >= 0 && y < 4 && y >= 0){
          byte red = min(255, matrix[x][y] + ripples[i];
          byte green = min(255, matrix[x][y] + ripples[i];
          byte blue = min(255, matrix[x][y] + ripples[i];
          matrix[x][y] = red;
          matrix[x][y] = green;
          matrix[x][y] = blue;

      if(ripples[i].t >= FALLOFF_TIME) ripples[i].center = -1;

    for(int x=0; x<4; x++){
      for(int y=0; y<4; y++)
        trellis.pixels.setPixelColor(MATRIX_POINT(x,y), matrix[x][y].reg);

void loop() {
I2C is a shared bus. As long as the devices addresses don't overlap, you should be able to put the trellis on the standard I2C bus. The Teensy audio shield uses addresses 0x0A and 0x1A to set up the parameters for the audio shield.

If you use a third party library like the trellis library, it may not have an option to use the 2nd or 3rd I2C buses. If it does have the support, you would need to look at the constructor to see what is needed to change to use the 2nd I2C bus.

From the Adafruit documentation, it looks like trellis uses addresses 0x2E through 0x33.

However, you do want to change the following:

#define INT_PIN 10 // Change this to the pin connected to your interrupt

to use a different pin than pin #10 (which is the CS pin on the audio shield for the SD card, and 6 is the CS pin for the flash memory support). In practice it may not matter if you never put a SD card into the audio shield, but it is probably helpful to use a different just in case.
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I can confirm that using several I2C devices on the same bus together with the audio board is working. I am successfully using a display and accelerometer.