Don’t be alarmed by the size of the code below…it’s actually more comments than code, to walk you through what it’s doing.

This example demonstrates some basics of using the LED rings and the driver board’s accelerometer.

Although the driver board has a clicky button that can be used for input (PIN_BUTTON1 or digital pin 4 in Arduino), this is one of those “make you think” projects: what if, instead explicitly interacting with devices, they anticipated our needs and did what we want? This is normally a pair of festive Halloween glasses…but when you look down (as when navigating steps or looking in your candy bag) it transitions into bright headlights. Look up again and it’s back to Halloween mode.

This also demonstrates the accelerometer’s tap-detect function (just tap the glasses to select among different color schemes) and smooth “easing” interpolation between colors that gives things a touch of luxury.

The driver board is normally mounted on an eyeglass frame’s temple, with the STEMMA QT connector toward the front. If the code’s look-down behavior seems wrong, it may be that the glasses are folded or the board isn’t mounted the right way.

In addition to the Adafruit_IS31FL3741 library, this also requires the Adafruit_Sensor and Adafruit_LIS3DH libraries.

There’s also a CircuitPython version of this project on an earlier page.

If you’d prefer a pre-compiled binary: download this .UF2 file. Connect the EyeLights driver board to your computer with a USB cable, set the power switch “on,” double-tap the reset button and a small flash drive named GLASSESBOOT appears. Then drag the .UF2 file to GLASSESBOOT and wait several seconds while it copies.

// SPDX-FileCopyrightText: 2021 Phil Burgess for Adafruit Industries
// SPDX-License-Identifier: MIT

ACCELEROMETER INPUT DEMO: while the LED Glasses Driver has a perfectly
good clicky button for input, this code shows how one might instead use
the onboard accelerometer for interactions*.

Worn normally, the LED rings are simply lit a solid color.
TAP the eyeglass frames to cycle among a list of available colors.
LOOK DOWN to light the LED rings bright white -- for navigating steps
or finding the right key. LOOK BACK UP to return to solid color.
This uses only the rings, not the matrix portion.

* Like, if you have big ol' monster hands, that little button can be
  hard to click, y'know?

#include <Adafruit_IS31FL3741.h> // For LED driver
#include <Adafruit_LIS3DH.h>     // For accelerometer
#include <Adafruit_Sensor.h>     // For m/s^2 accel units

Adafruit_LIS3DH             accel;
Adafruit_EyeLights_buffered glasses; // Buffered for smooth animation

// Here's a list of colors that we cycle through when tapped, specified
// as {R,G,B} values from 0-255. These are intentionally a bit dim --
// both to save battery and to make the "ground light" mode more dramatic.
// Rather than primary color red/green/blue sequence which is just so
// over-done at this point, let's use some HALLOWEEN colors!
uint8_t colors[][3] = {
  {27, 9, 0},  // Orange
  {12, 0, 24}, // Purple
  {5, 31, 0},  // Green
#define NUM_COLORS (sizeof colors / sizeof colors[0]) // List length
uint8_t looking_down_color[] = {255, 255, 255};       // Max white

uint8_t  color_index = 0;   // Begin at first color in list
uint8_t *target_color;      // Pointer to color we're aiming for
float    interpolated_color[] = {0.0, 0.0, 0.0}; // Current color along the way
float    filtered_y;        // De-noised accelerometer reading
bool     looking_down;      // Set true when glasses are oriented downward
sensors_event_t event;      // For accelerometer conversion
uint32_t last_tap_time = 0; // For accelerometer tap de-noising

// Crude error handler, prints message to Serial console, flashes LED
void err(char *str, uint8_t hz) {
  for (;;) digitalWrite(LED_BUILTIN, (millis() * hz / 500) & 1);

void setup() { // Runs once at program start...

  // Initialize hardware
  if (! accel.begin())   err("LIS3DH not found", 5);
  if (! glasses.begin()) err("IS3741 not found", 2);

  // Configure accelerometer and get initial state
  accel.setClick(1, 100); // Set threshold for single tap
  accel.getEvent(&event); // Current accel in m/s^2
  // Check accelerometer to see if we've started in the looking-down state,
  // set the target color (what we're aiming for) appropriately. Only the
  // Y axis is needed for this.
  filtered_y = event.acceleration.y;
  looking_down = (filtered_y > 5.0);
  // If initially looking down, aim for the look-down color,
  // else aim for the first item in the color list.
  target_color = looking_down ? looking_down_color : colors[color_index];

  // Configure glasses for max brightness, enable output

void loop() { // Repeat forever...

  // interpolated_color blends from the prior to the next ("target")
  // LED ring colors, with a pleasant ease-out effect.
  for(uint8_t i=0; i<3; i++) { // R, G, B
    interpolated_color[i] = interpolated_color[i] * 0.97 + target_color[i] * 0.03;
  // Convert separate red, green, blue to "packed" 24-bit RGB value
  uint32_t rgb = ((int)interpolated_color[0] << 16) |
                 ((int)interpolated_color[1] << 8) |
  // Fill both rings with packed color, then refresh the LEDs.

  // The look-down detection only needs the accelerometer's Y axis.
  // This works with the Glasses Driver mounted on either temple,
  // with the glasses arms "open" (as when worn).
  // Smooth the accelerometer reading the same way RGB colors are
  // interpolated. This avoids false triggers from jostling around.
  filtered_y = filtered_y * 0.97 + event.acceleration.y * 0.03;

  // The threshold between "looking down" and "looking up" depends
  // on which of those states we're currently in. This is an example
  // of hysteresis in software...a change of direction requires a
  // little extra push before it takes, which avoids oscillating if
  // there was just a single threshold both ways.
  if (looking_down) {       // Currently in the looking-down state...
    (void)accel.getClick(); // Discard any taps while looking down
    if (filtered_y < 3.5) { // Have we crossed the look-up threshold?
      target_color = colors[color_index]; // Back to list color
      looking_down = false;               // We're looking up now!
  } else {                  // Currently in the looking-up state...
    if (filtered_y > 5.0) { // Crossed the look-down threshold?
      target_color = looking_down_color; // Aim for white
      looking_down = true;               // We're looking down now!
    } else if (accel.getClick()) {
      // No look up/down change, but the accelerometer registered
      // a tap. Compare this against the last time we sensed one,
      // and only do things if it's been more than half a second.
      // This avoids spurious double-taps that can occur no matter
      // how carefully the tap threshold was set.
      uint32_t now = millis();
      uint32_t elapsed = now - last_tap_time;
      if (elapsed > 500) {
        // A good tap was detected. Cycle to the next color in
        // the list and note the time of this tap.
        color_index = (color_index + 1) % NUM_COLORS;
        target_color = colors[color_index];
        last_tap_time = now;

This guide was first published on Oct 12, 2021. It was last updated on Jul 18, 2024.

This page (Tap-and-Look Glasses) was last updated on Jul 18, 2024.

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