The Arduino code presented below works equally well on all versions of GEMMA: v1, v2 and M0. But if you have an M0 board, consider using the CircuitPython code on the next page of this guide, no Arduino IDE required!

Upload the code below to GEMMA to see the interactive color changing effect using the soft potentiometer. This sketch doesn't do any smoothing of the sensor value before directly mapping it to a color, so the LEDs will flash different colors as you slide, then stay on a single color when you let go of the slide charm. We wanted to keep the code as simple as possible so you can learn exactly how the sensor works, so feel free to upgrade it to suit your project's needs!

// SPDX-FileCopyrightText: 2017 Mikey Sklar for Adafruit Industries
// SPDX-License-Identifier: MIT

#include <Adafruit_NeoPixel.h>

#define PIN 1
// Parameter 1 = number of pixels in strip
// Parameter 2 = Arduino pin number (most are valid)
// Parameter 3 = pixel type flags, add together as needed:
//   NEO_KHZ800  800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)
//   NEO_KHZ400  400 KHz (classic 'v1' (not v2) FLORA pixels, WS2811 drivers)
//   NEO_GRB     Pixels are wired for GRB bitstream (most NeoPixel products)
//   NEO_RGB     Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)
Adafruit_NeoPixel strip = Adafruit_NeoPixel(8, PIN, NEO_GRB + NEO_KHZ800);

int sensorPin = 1;    // select the input pin for the potentiometer (analog 1 is digital 2)
int sensorValue = 0;  // variable to store the value coming from the sensor
int colorValue = 0;

void setup() {
  // Set internal pullup resistor for sensor pin (analog 1 is digital 2)
  pinMode(2, INPUT_PULLUP); 
  strip.setBrightness(40); //adjust brightness here; // Initialize all pixels to 'off'

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);
  colorValue = map(sensorValue, 0, 1024, 0, 255); //map sensor values from 0-124 to 0-255
  for (int i = 0; i<strip.numPixels(); i++){
    strip.setPixelColor(i, Wheel(colorValue)); //use Wheel function to set color

// Input a value 0 to 255 to get a color value.
// The colours are a transition r - g - b - back to r.
uint32_t Wheel(byte WheelPos) {
  if(WheelPos < 85) {
   return strip.Color(WheelPos * 3, 255 - WheelPos * 3, 0);
  } else if(WheelPos < 170) {
   WheelPos -= 85;
   return strip.Color(255 - WheelPos * 3, 0, WheelPos * 3);
  } else {
   WheelPos -= 170;
   return strip.Color(0, WheelPos * 3, 255 - WheelPos * 3);

If this is your first time using GEMMA, work through the Introducing GEMMA guide first; you need to customize some settings in the Arduino IDE. Once you have it up and running (test the 'blink' sketch), then follow the instructions on the following page for installing the NeoPixel library:

NeoPixel Überguide: Arduino Library Installation

Plug in your circuit and load up the sketch below:

This guide was first published on Feb 11, 2015. It was last updated on Jul 24, 2024.

This page (Arduino Code) was last updated on Jul 21, 2024.

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