Xmas_tree.ino

Brief Code Documentation

CONSTANTS

ROW_HOLD_TIME         // Time Interval (us) a Row value cannot change
COLUMN_HOLD_TIME      // Time Interval (us) a Row value cannot change
RND_LED_HOLD_TIME     // Base Time Interval (us) a LED is ON in the Random Mode
SPIRAL_LED_HOLD_TIME  // Time Interval (ms) a LED is ON in the Spiral Mode 
N_PERSIST_ITER        // Number of iterations a LED state persists

Functions

// Implements the Random Generator Algorithm
uint8_t lfsr();

// "moves" the active leds one row up
void ascend();

// "moves" the active leds one row down
void descend();

// Complete sequence: "moves" the active leds up and down across all rows
void ascend_and_descend();

// "moves" the active leds one column clockwise
void clockwise();

// "moves" the active leds one column counter_clockwise
void counter_clockwise();

// "moves" the only active led spirally
// clockwise and then one row down
void spiral_down_clockwise();

// "moves" the only active led spirally
// counter_clockwise and then one row up
void spiral_up_counter_clockwise();

// Blinks all leds
void blink();

/*
 * Random LED Behaviour
 *
 * INPUTS
 *    - n_leds: number of leds to be active during the time interval
 *    - faster: boolean variable that selects the LEDs alternation speed
 *    - scale_factor: increases the time of the function execution
 *
 */
void random_seq(uint8_t n_leds, uint8_t faster, uint8_t scale_factor);

// Abstraction layer for setting rows & columns
void set_columns(uint8_t columns);
void set_rows(uint8_t rows);

Pseudo-Random Algorithm

The Random Algorithm used to generate the random LEDs sequences is a Linear-feedback shift register (LSFR)
These pseudo-random algorithm aplies a polynomial transformation to a given seed, through a sequence of XOR operations and bit shifts. This set of operations results in a new pseudo-random bit that is either retrieved and concatenated to the binary data string

For more informations, visit the Wikipedia Page on LSFR