Is there an easy way to select a set of leds from a CRGBArray

Stephen_Kramer · April 5, 2018, 4:59pm

Is there an easy way to select a set of leds from a CRGBArray where the end pixel is before the start pixel, such that the set starts at the ‘start’ led, wraps around at the end of the strip and continues at the start of the strip and ends at the end led, whose number is less than the start led. So you can easily have a movable set that automatically wraps around the end of the strip back to the beginning?

marmil · April 5, 2018, 5:38pm

Modulo might be what you’re looking for. Here’s an example.

github.com

marmilicious/FastLED_examples/blob/master/three_moving_pixels_v3.ino

//***************************************************************
// Three moving pixels example
//     Uses modulo, %, to make pixel position "loop" around and
//     stay in valid pixel range.
//
// Marc Miller, Feb 2015.  Updated Jan 2016.
//***************************************************************


#include "FastLED.h"
#define LED_TYPE NEOPIXEL  // Strip type: NEOPIXEL, APA102, LPD8806, etc.
#define DATA_PIN 6
//#define CLOCK_PIN 13
#define NUM_LEDS 12
//#define COLOR_ORDER BGR
#define MASTER_BRIGHTNESS 100  // Master brightness (Range is 0-255)
CRGB leds[NUM_LEDS];

int16_t positionRed = 0;    // Set initial start position of Red pixel
int16_t positionWhite = 4;  // Set initial start position of White pixel

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marmil · April 5, 2018, 5:42pm

More examples that used modulo.

github.com

marmilicious/FastLED_examples/blob/master/beat8.ino

//***************************************************************
// beat8 example.  Moves pixel position based on beat8.
//
// -Marc Miller, Jan 2016
// Updated Feb 2016 - made move speed and fade rate variables.
//***************************************************************

#include "FastLED.h"
#define LED_TYPE LPD8806
#define DATA_PIN 11
#define CLOCK_PIN 13
#define NUM_LEDS 32
#define COLOR_ORDER GRB
#define BRIGHTNESS 50
CRGB leds[NUM_LEDS];

uint8_t gHue = 0;  // Used to cycle through rainbow.
uint8_t moveSpeed = 6;  // Higher value moves pixel faster.
uint8_t fadeRate = 80;  // Use lower value to give a fading tail.

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github.com

marmilicious/FastLED_examples/blob/master/moving_gradient_example.ino

//***************************************************************
// Moving gradient example
// It will wrap around, and the direction can be reversed.
// This is done a bit different then you might expect as I'm
// filling the gradient once in setup() and saving the colors
// in a seperate CRGB array.  Then coping those into the main
// leds array as needed when moving it around.
//
// Marc Miller, Jan 2016
//***************************************************************

#include "FastLED.h"
#define LED_TYPE LPD8806
#define DATA_PIN 11
#define CLOCK_PIN 13
#define NUM_LEDS 32
#define COLOR_ORDER GRB
#define BRIGHTNESS 255
CRGB leds[NUM_LEDS];

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Andrew_Tuline · April 5, 2018, 5:48pm

In addition to Modulo, there’s also the beat8() function which is a sawtooth wave. The advantage here is that you don’t have to use a delay() statement to slow down the animation. The disadvantage is that if you change the rate on the fly, the returned value will jump significantly. Also, unlike some of the beat functions, beat8() does not have min and max options, so the returned uint8_t value will probably need to be mapped to the length of your strand.