This is another example demonstrating the LED rings and accelerometer, not the matrix portion of the glasses yet. The rings swivel and spin in response to movement, as if filled with liquid, or like jiggling plastic “googly eyes.” The idea and math are adapted from an earlier project, Bill Earl's STEAM-Punk Goggles.

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

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

GOOGLY EYES for Adafruit EyeLight LED glasses + driver. Pendulum physics
simulation using accelerometer and math. This uses only the rings, not the
matrix portion. Adapted from Bill Earl's STEAM-Punk Goggles project:

#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

// A small class for our pendulum simulation.
class Pendulum {
  // Constructor. Pass pointer to EyeLights ring, and a 3-byte color array.
  Pendulum(Adafruit_EyeLights_Ring_buffered *r, uint8_t *c) {
    ring  = r;
    color = c;
    // Initial pendulum position, plus axle friction, are randomized
    // so rings don't spin in perfect lockstep.
    angle = random(1000);
    momentum = 0.0;
    friction = 0.94 + random(300) * 0.0001; // Inverse friction, really

  // Given a pixel index (0-23) and a scaling factor (0.0-1.0),
  // interpolate between LED "off" color (at 0.0) and this item's fully-
  // lit color (at 1.0) and set pixel to the result.
  void interp(uint8_t pixel, float scale) {
    // Convert separate red, green, blue to "packed" 24-bit RGB value
        (int(color[0] * scale) << 16) |
        (int(color[1] * scale) <<  8) |
         int(color[2] * scale));

  // Given an accelerometer reading, run one cycle of the pendulum
  // physics simulation and render the corresponding LED ring.
  void iterate(sensors_event_t &event) {
    // Minus here is because LED pixel indices run clockwise vs. trigwise.
    // 0.006 is just an empirically-derived scaling fudge factor that looks
    // good; smaller values for more sluggish rings, higher = more twitch.
    momentum =  momentum * friction - 0.006 *
      (cos(angle) * event.acceleration.z +
       sin(angle) * event.acceleration.x);
    angle += momentum;

    // Scale pendulum angle into pixel space
    float midpoint = fmodf(angle * 12.0 / M_PI, 24.0);

    // Go around the whole ring, setting each pixel based on proximity
    // (this is also to erase the prior position)...
    for (uint8_t i=0; i<24; i++) {
        float dist = fabs(midpoint - (float)i); // Pixel to pendulum distance...
        if (dist > 12.0)                   // If it crosses the "seam" at top,
            dist = 24.0 - dist;            //   take the shorter path.
        if (dist > 5.0)                    // Not close to pendulum,
            ring->setPixelColor(i, 0);     //   erase pixel.
        else if (dist < 2.0)               // Close to pendulum,
            interp(i, 1.0);                //   solid color
        else                               // Anything in-between,
            interp(i, (5.0 - dist) / 3.0); //   interpolate
  Adafruit_EyeLights_Ring_buffered *ring; // -> glasses ring
  uint8_t *color;    // -> array of 3 uint8_t's [R,G,B]
  float    angle;    // Current position around ring
  float    momentum; // Current 'oomph'
  float    friction; // A scaling constant to dampen motion

Pendulum pendulums[] = {
    Pendulum(&glasses.left_ring, (uint8_t[3]){0, 20, 50}),  // Cerulean blue,
    Pendulum(&glasses.right_ring, (uint8_t[3]){0, 20, 50}), // 50 is plenty bright!
#define N_PENDULUMS (sizeof pendulums / sizeof pendulums[0])

// 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 glasses for max brightness, enable output

void loop() { // Repeat forever...
  sensors_event_t event;
  accel.getEvent(&event); // Read accelerometer once
  for (uint8_t i=0; i<N_PENDULUMS; i++) { // For each pendulum...
    pendulums[i].iterate(event);          // Do math with accel data

This guide was first published on Oct 12, 2021. It was last updated on 2022-02-14 16:45:58 -0500.

This page (Googly Eye Rings) was last updated on Aug 27, 2022.

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