Paints a sine wave pattern to a variable number of TLC5971 chips.

TLC5971 Arduino Sine.jpg

TLC5971-arduino-sine.ino

/* 
 * Paints a sine wave pattern to a variable number of TLC5971 chips.
 * Animates with time on a 2-second loop.
 * Assumes monochrome, but should look good on RGB too.
 * Only tested on Arduino Due. Framerate may suffer on Uno.
 * 
 * :: PACKET STRUCTURE ::
 * 224 bit shift register
 *  | 32 bit header
 *     | 6 bit WC (Write Command)
 *     | 5 bit FC (Function Control)
 *     | 21 bit BC (Brightness Control)
 *        | 7 bit Blue (0-3)
 *        | 7 bit Green (0-3)
 *        | 7 bit Red (0-3)
 *  | 192 bit GS (GrayScale)
 *     | 16 bit Blue3
 *     | 16 bit Green3
 *     | 16 bit Red3
 *     | 16 bit Blue2
 *      ...
 *     | 16 bit Red0
 */

const int DATA = 2; // SDI pin
const int CLOCK = 3; // SCK pin

const int PACKET_BYTES = 28;
const int REGISTER_COUNT = 10; // How many chips are in series?

void setup() {
  pinMode(DATA, OUTPUT);
  pinMode(CLOCK, OUTPUT);
}

void writeHeaderToPacket(byte packet[], byte brightness = 0xFF) {
  // Use a 32-bit long to collect 6 WC, 5 FC, and 21 BC
  //              |6 WC|
  //                    |5FC|
  long header = 0b10010100010 << (32-6-5);

  // Use same brightness control for all 3 colors
  brightness >>= 1; // cut brightness down to 7 bits
  header |= brightness;              // BC red
  header |= (long)brightness << 7;   // BC green
  header |= (long)brightness << 7*2; // BC blue

  // Copy to packet
  packet[0] = header >> 8*3;
  packet[1] = header >> 8*2;
  packet[2] = header >> 8;
  packet[3] = header;
}

void writeSineWaveToPacket(byte packet[], unsigned long t = millis(),
                           float phaseShift = 0, float period = 12) {
  const static int C = (1 << 15) - 1;
  const float iScale = 2*PI / period;
  const static float tScale = 2*PI / 2000; // 2-second loop
  const float tShift = t * tScale;
  for (int i = 0; i < 12; i++) {
    float angle = (i + phaseShift)*iScale + tShift;
    int value = C*cos(angle) + C;
    
    packet[i*2 + 4] = value >> 8;
    packet[i*2 + 5] = value;
  }
}

void writePacketToShiftRegister(byte packet[]) {
  for (byte i = 0; i < PACKET_BYTES; i++) {
    shiftOut(DATA, CLOCK, MSBFIRST, packet[i]); 
  }
}

void loop() {
  byte packets[REGISTER_COUNT][PACKET_BYTES];

  // first, compute data for one frame
  const unsigned long t = millis();
  for (int i = 0; i < REGISTER_COUNT; i++) {
    writeHeaderToPacket(packets[i], 0x33); // brightness up to 0xFF
    writeSineWaveToPacket(packets[i], t, 12*i, 12*REGISTER_COUNT);
  }

  // then, shift it all out
  for (int i = 0; i < REGISTER_COUNT; i++) {
    writePacketToShiftRegister(packets[i]);
  }
}