I'm trying to use a distance sensor to trigger an LED light, as you can see below. However, I also want the LED to stay on/white when a person is within the 38 inches range. How should I do that?

//Tell the Arduino IDE to include the FastLED library
#include <FastLED.h>

//Setup the variables for the HC-SR04
const int trigPin = 9;
const int echoPin = 6;
//Setup the variables for the NeoPixel Strip
#define NUM_LEDS 60 // How many leds in your strip?
#define DATA_PIN 4 // What pin is the NeoPixel's data line connected to?
CRGB leds[NUM_LEDS]; // Define the array of leds

void setup() {
  // initialize serial communication:
  FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);

void loop() {
  // establish variables for duration of the ping,
  // and the distance result in inches and centimeters:
  long duration, inches, cm;

  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  pinMode(trigPin, OUTPUT);
  digitalWrite(trigPin, LOW);
  digitalWrite(trigPin, HIGH);
  digitalWrite(trigPin, LOW);

  // Read the signal from the sensor: a HIGH pulse whose
  // duration is the time (in microseconds) from the sending
  // of the ping to the reception of its echo off of an object.
  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);

  // convert the time into a distance
  inches = microsecondsToInches(duration);
  cm = microsecondsToCentimeters(duration);

  Serial.print("in, ");
  if (inches <= 38)  {
    for ( int colorStep = 0; colorStep < 256; colorStep++ ) {
      int r = 255 - colorStep;
      // Redness starts at zero and goes up to full
      int b = 255 - colorStep;
      // Blue starts at full and goes down to zero
      int g = 255 - colorStep;
      // No green needed to go from blue to red
      // Now loop though each of the LEDs and set each one to the current color
      for (int x = 0; x < NUM_LEDS; x++) {
        leds[x] = CRGB(r, g, b);
      // Display the colors we just set on the actual LEDs
  } else if (inches > 38) {
    fill_solid( &(leds[0]), NUM_LEDS /*number of leds*/, CRGB::Black);

long microsecondsToInches(long microseconds) {
  // According to Parallax's datasheet for the PING))), there are
  // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
  // second). This gives the distance travelled by the ping, outbound
  // and return, so we divide by 2 to get the distance of the obstacle.
  // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
  return microseconds / 74 / 2;

long microsecondsToCentimeters(long microseconds) {
  // The speed of sound is 340 m/s or 29 microseconds per centimeter.
  // The ping travels out and back, so to find the distance of the
  // object we take half of the distance travelled.
  return microseconds / 29 / 2;
  • 1
    Your code appears to be doing just that. Could you explain what the current code is doing, that you want different? – Gerben Apr 26 '16 at 18:46
  • You could set the pinmodes in the setup, for improved performance, but other than that, your code looks sane. As Gerben said, what is the actual problem here? Try uncommenting the "fill solid white" function in your if? En commenting the colorwheel thingy – Paul Mar 24 '17 at 7:23

if (inches <= 38)

That You might want to change. Try using "while(inches <= 38)" and moving sensor calculations to that loop. When ever the distance stays less than You want the light should stay on.

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