How to Optimally Shift Large Arrays n Number of Incidences

Question

I am creating my own version of a music visualizer that responds to the frequency of music; a common project. I am using 2 strips of Neopixels, each with 300 LEDs making a total of 600 LEDs.

I have written functions, shown below, that create the desired affect of having a pulse of light travel down the strips independently. However, when running in real time with music, the updates per second is too slow to create a nice pulse; it looks choppy.

I believe the problem is the number of operations that must be preformed when the function is called. For each call to the function, a 300 value array per strip must be shifted 5 indices and 5 new values added.

Here is an illustration of how the function currently works:

-Arbitrary numbers are used to fill the array

-A shift of 2 indices shown

-X represents an index with no value assigned

-N represents the new value added by the function

Initial array: [1][3][7][2][9]
Shifted array: [X][X][1][3][7]
New array:     [N][N][1][3][7]

Here if my code. Function declarations below loop(). I am using random() to trigger a pulse for testing purposes; no other functions were included for brevity.

#include <FastLED.h>

// ========================= Define setup parameters =========================
#define NUM_LEDS1 300                    // Number of LEDS in strip 1
#define NUM_LEDS2 300                    // Number of LEDS in strip 1
#define STRIP1_PIN 6                     // Pin number for strip 1
#define STRIP2_PIN 10                    // Pin number for strip 2
#define s1Band 1                         // String 1 band index
#define s2Band 5                         // String 2 band index
#define numUpdate 5                      // Number of LEDs that will be used for a single pulse  

// Colors for strip 1: Band 2 (Index 1)
#define s1R 255
#define s1G 0
#define s1B 0
// Colors for strip 2: Band 6 (Index 5)
#define s2R 0
#define s2G 0
#define s2B 255


// Create the arrays of LEDs
CRGB strip1[NUM_LEDS1];
CRGB strip2[NUM_LEDS2];



void setup() {

  FastLED.addLeds<NEOPIXEL, STRIP1_PIN>(strip1, NUM_LEDS1);
  FastLED.addLeds<NEOPIXEL, STRIP2_PIN>(strip2, NUM_LEDS2);
  FastLED.setBrightness(10);
  FastLED.clear();
  FastLED.show();

}

void loop() {

  int num = random(0, 31);

  // Pulse strip based on random number for testing
  if (num == 5) {
    pulseDownStrip1();
  }

  pulseBlack1();

}




// ======================= FUNCTION DECLARATIONS =======================

// Pulse a set of colored LEDs down the strip
void pulseDownStrip1() {

  // Move all current LED states by n number of leds to be updated
  for (int i = NUM_LEDS1 - 1; i >= 0; i--) {
    strip1[i] = strip1[i - numUpdate];
  }

  // Add new LED values to the pulse
  for (int j = 0; j < numUpdate; j++) {
    strip1[j].setRGB(s1R, s1G, s1B);
  }

  FastLED.show();

}

// Pulse a set of black LEDs down the strip
void pulseBlack1(){

  // Move all current LED states by n number of leds to be updated
  for (int i = NUM_LEDS1 - 1; i >= 0; i--) {
    strip1[i] = strip1[i - numUpdate];
  }

  // Add new LED values to the pulse
  for (int j = 0; j < numUpdate; j++) {
    strip1[j].setRGB(0, 0, 0);
  }

  FastLED.show();

}

I am looking for any suggestions regarding optimizing this operation. Through my research, copying the desired values to a new array rather than shifting the existing array seems to be a faster operation.

If you have any advice on optimizing this process, or alternate methods to produce the same animation, I would appreciate the help.

score 0 · Answer 1 · answered Jul 13 '19 at 18:30

The secret is to not shift it. Shift where you start reading it instead. Keep track of a separate variable that keeps the start position and alter your reading through the array to start there, roll back over to zero when it gets to the array length, and stop one short of where it starts.

Google the term "circular buffer" Look at the Arduino HardwareSerial class for a decent implementation example.

How to Optimally Shift Large Arrays n Number of Incidences

1 Answers1