A Squirrel program to display characters and graphics on an 8 x 8 LED matrix connect to an Imp device.

led_matrix_01.device.nut

// Matrix LED character set display by Tony Smith
// Based on code from LinkSprite: 
// [http://linksprite.com/wiki/index.php5?title=LED_Matrix_Kit]
// Additional code copyright © Electric Imp, 2014
// Maxim Integrated Max7219 Datasheet: 
// [http://www.maximintegrated.com/datasheet/index.mvp/id/1339]
 
// Set the number of available characters in the character set
const alpha_count = 95;    
 
// Set up recognisable aliases for the three Imp GPIO pins
led_clk <- hardware.pin9;
led_cs <- hardware.pin8;
led_din <- hardware.pin7;
 
// Set these pins as digital outputs
led_clk.configure(DIGITAL_OUT);
led_cs.configure(DIGITAL_OUT);
led_din.configure(DIGITAL_OUT);
 
// Establish an array of 8 x 8 character matrices
// Have fun making up your own characters!
charset <- [
[0x0,0x0,0x0,0x0,0x0,0x0,0x0,0x0],		// Space - Ascii 32
[0x0,0x10,0x10,0x10,0x10,0x0,0x10,0x0],		// !
[0x0,0x24,0x24,0x0,0x0,0x0,0x0,0x0],		// ”
[0x0,0x24,0x7E,0x24,0x24,0x7E,0x24,0x0],	// #
[0x0,0x8,0x3E,0x28,0x3E,0xA,0x3E,0x8],		// $
[0x0,0x62,0x64,0x8,0x10,0x26,0x46,0x0],		// %
[0x0,0x10,0x28,0x10,0x2A,0x44,0x3A,0x0],	// &
[0x0,0x8,0x10,0x0,0x0,0x0,0x0,0x0],		// ‘
[0x0,0x4,0x8,0x8,0x8,0x8,0x4,0x0],		// (
[0x0,0x20,0x10,0x10,0x10,0x10,0x20,0x0],	// )
[0x0,0x0,0x14,0x8,0x3E,0x8,0x14,0x0],		// *
[0x0,0x0,0x8,0x8,0x3E,0x8,0x8,0x0],		// +
[0x0,0x0,0x0,0x0,0x0,0x8,0x8,0x10],		// ,
[0x0,0x0,0x0,0x0,0x3E,0x0,0x0,0x0],		// -
[0x0,0x0,0x0,0x0,0x0,0x18,0x18,0x0],		// .
[0x0,0x2,0x4,0x8,0x10,0x20,0x40,0x0],		// /
[0x0,0x3C,0x46,0x4A,0x52,0x62,0x3C,0x0],	// 0 - Ascii 48
[0x0,0x30,0x50,0x10,0x10,0x10,0x7C,0x0],	// 1
[0x0,0x3C,0x42,0x2,0x3C,0x40,0x7E,0x0],		// 2
[0x0,0x3C,0x42,0xC,0x2,0x42,0x3C,0x0],		// 3
[0x0,0x8,0x18,0x28,0x48,0x7E,0x8,0x0],		// 4
[0x0,0x7E,0x40,0x7C,0x2,0x42,0x3C,0x0],		// 5
[0x0,0x3C,0x40,0x7C,0x42,0x42,0x3C,0x0],	// 6
[0x0,0x7E,0x2,0x4,0x8,0x10,0x10,0x0],		// 7
[0x0,0x3C,0x42,0x3C,0x42,0x42,0x3C,0x0],	// 8
[0x0,0x3C,0x42,0x42,0x3E,0x2,0x3C,0x0],		// 9
[0x0,0x0,0x10,0x0,0x0,0x0,0x10,0x0],		// : - Ascii 58
[0x0,0x0,0x10,0x0,0x0,0x10,0x10,0x20],		// ;
[0x0,0x0,0x4,0x8,0x10,0x8,0x4,0x0],		// <
[0x0,0x0,0x0,0x3E,0x0,0x3E,0x0,0x0],		// =
[0x0,0x0,0x10,0x8,0x4,0x8,0x10,0x0],		// >
[0x0,0x3C,0x42,0x4,0x8,0x0,0x8,0x0],		// ?
[0x0,0x3C,0x4A,0x56,0x5E,0x40,0x3C,0x0],	// @
[0x0,0x3C,0x42,0x42,0x7E,0x42,0x42,0x0],	// A - Ascii 65
[0x0,0x7C,0x42,0x7C,0x42,0x42,0x7C,0x0],	// B
[0x0,0x3C,0x42,0x40,0x40,0x42,0x3C,0x0],	// C
[0x0,0x78,0x44,0x42,0x42,0x44,0x78,0x0],	// D
[0x0,0x7E,0x40,0x7C,0x40,0x40,0x7E,0x0],	// E
[0x0,0x7E,0x40,0x7C,0x40,0x40,0x40,0x0],	// F
[0x0,0x3C,0x42,0x40,0x4E,0x42,0x3C,0x0],	// G
[0x0,0x42,0x42,0x7E,0x42,0x42,0x42,0x0],	// H
[0x0,0x7C,0x10,0x10,0x10,0x10,0x7C,0x0],	// I
[0x0,0x2,0x2,0x2,0x2,0x42,0x3C,0x0],		// J
[0x0,0x44,0x48,0x70,0x48,0x44,0x42,0x0],	// K
[0x0,0x40,0x40,0x40,0x40,0x40,0x7E,0x0],	// L
[0x0,0x42,0x66,0x5A,0x42,0x42,0x42,0x0],	// M
[0x0,0x42,0x62,0x52,0x4A,0x46,0x42,0x0],	// N
[0x0,0x3C,0x42,0x42,0x42,0x42,0x3C,0x0],	// O
[0x0,0x7C,0x42,0x42,0x7C,0x40,0x40,0x0],	// P
[0x0,0x3C,0x42,0x42,0x52,0x4A,0x3C,0x0],	// Q
[0x0,0x7C,0x42,0x42,0x7C,0x44,0x42,0x0],	// R
[0x0,0x3C,0x40,0x3C,0x2,0x42,0x3C,0x0],		// S
[0x0,0x7C,0x10,0x10,0x10,0x10,0x10,0x0],	// T
[0x0,0x42,0x42,0x42,0x42,0x42,0x3C,0x0],	// U
[0x0,0x42,0x42,0x42,0x42,0x24,0x18,0x0],	// V
[0x0,0x42,0x42,0x42,0x42,0x5A,0x24,0x0],	// W
[0x0,0x42,0x24,0x18,0x18,0x24,0x42,0x0],	// X
[0x0,0x44,0x28,0x10,0x10,0x10,0x10,0x0],	// Y
[0x0,0x7E,0x4,0x8,0x10,0x20,0x7E,0x0],		// Z - Ascii 90
[0x0,0xE,0x8,0x8,0x8,0x8,0xE,0x0],		// [
[0x0,0x0,0x40,0x20,0x10,0x8,0x4,0x0],		// \
[0x0,0x70,0x10,0x10,0x10,0x10,0x70,0x0],	// ]
[0x0,0x10,0x38,0x54,0x10,0x10,0x10,0x0],	// ^
[0x0,0x0,0x0,0x0,0x0,0x0,0x0,0xFF],		// _
[0x0,0x1C,0x22,0x78,0x20,0x20,0x7E,0x0],	// £
[0x0,0x0,0x38,0x4,0x3C,0x44,0x3C,0x0],		// a - Ascii 97
[0x0,0x40,0x40,0x78,0x44,0x44,0x78,0x0],	// b
[0x0,0x0,0x38,0x40,0x40,0x40,0x38,0x0],		// c
[0x0,0x4,0x4,0x3C,0x44,0x44,0x3C,0x0],		// d
[0x0,0x0,0x38,0x44,0x78,0x40,0x3C,0x0],		// e
[0x0,0x30,0x40,0x60,0x40,0x40,0x40,0x0],	// f
[0x0,0x3C,0x44,0x44,0x3C,0x4,0x38,0x0],		// g
[0x0,0x40,0x40,0x40,0x78,0x44,0x44,0x0],	// h
[0x0,0x20,0x0,0x60,0x20,0x20,0x70,0x0],		// i
[0x0,0x8,0x0,0x8,0x8,0x48,0x30,0x0],		// j
[0x0,0x40,0x50,0x60,0x60,0x50,0x48,0x0],	// k
[0x0,0x40,0x40,0x40,0x40,0x40,0x30,0x0],	// l
[0x0,0x0,0x68,0x54,0x54,0x54,0x54,0x0],	    	// m
[0x0,0x0,0x78,0x44,0x44,0x44,0x44,0x0],    	// n
[0x0,0x0,0x38,0x44,0x44,0x44,0x38,0x0],		// o
[0x0,0x78,0x44,0x44,0x78,0x40,0x40,0x0],	// p
[0x0,0x3C,0x44,0x44,0x3C,0x4,0x6,0x0],		// q
[0x0,0x0,0x1C,0x20,0x20,0x20,0x20,0x0],	   	// r
[0x0,0x0,0x38,0x40,0x38,0x4,0x78,0x0],		// s
[0x0,0x20,0x70,0x20,0x20,0x20,0x18,0x0],	// t
[0x0,0x0,0x44,0x44,0x44,0x44,0x38,0x0],		// u
[0x0,0x0,0x44,0x44,0x28,0x28,0x10,0x0],		// v
[0x0,0x0,0x44,0x54,0x54,0x54,0x28,0x0],		// w
[0x0,0x0,0x44,0x28,0x10,0x28,0x44,0x0],		// x
[0x0,0x0,0x44,0x44,0x3C,0x4,0x38,0x0],		// y
[0x0,0x0,0x7C,0x8,0x10,0x20,0x7C,0x0],		// z - Ascii 122
[0x0,0xE,0x8,0x30,0x8,0x8,0xE,0x0],		// {
[0x0,0x8,0x8,0x8,0x8,0x8,0x8,0x0],		// |
[0x0,0x70,0x10,0xC,0x10,0x10,0x70,0x0],		// }
[0x0,0x14,0x28,0x0,0x0,0x0,0x0,0x0],		// ~
[0x3C,0x42,0x99,0xA1,0xA1,0x99,0x42,0x3C],	// © - Ascii 127
];
 
// Define functions
function write_LED_byte(byte_value) {   
    // Writes a single byte of data to the MAX7219 display controller 
    // one bit at a time. Writes data to the LED in the MAX7219’s 16-bit
    // serial format, which puts the register address in the first eight 
    // bits then the data in the second set of eight bits.
    
    for (local i = 8 ; i > 0 ; i--) {		  
        led_clk.write(0);
        led_din.write(byte_value & 0x80); 	// Extract bit 8 and write it to LED
        byte_value = byte_value << 1;	        // Shift DATA bits left by one bit
        led_clk.write(1);
    }                                 
}
 
function write_LED(register_address, byte_value) {
    // Writes a single value to the MAX7219,
    // preceded by the register
    // it is being written to	
    led_cs.write(0);
    write_LED_byte(register_address);
    write_LED_byte(byte_value);
    led_cs.write(1);
}
 
function init_LED() {
    // Initialise the MAX7219’s parameter registers by writing
    // the register’s address followed by its 8-bit value
    write_LED(0x09, 0x00);       // Set MAX7219’s BCD decode mode to ‘none’
    write_LED(0x0a, 0x00);       // Set MAX7219’s LED intensity to a 2/32 duty cycle
    write_LED(0x0b, 0x07);       // Set MAX7219’s scan limit to all eight LED columns
    write_LED(0x0c, 0x01);       // Set MAX7219’s power mode. 0 = power down, 1 = normal
    write_LED(0x0f, 0x00);       // Set MAX7219’s display test mode off
 
    // Nb. BCD = Binary Coded Decimal
}
 
function delay(value) {
    // Delay for ‘value’ milliseconds
    local a = hardware.millis() + value;
    while (hardware.millis() < a) {
        // NOP
    }
}
 
function rotate_matrix(matrix_in) {
    // Rotate the character matrix through -90 degrees
    // Used if the LED matrix pins are connected directly to a breadboard
    local i = 0;
    local j = 0;
    local a = 0;
    local line_value = 0;
    local matrix_out = [0,0,0,0,0,0,0,0];
    
    for (i = 0 ; i < 8 ; i++) {
        line_value = matrix_in[i];
        for (j = 7 ; j > -1 ; j--) {
            a = (line_value & math.pow(2, j));
            if (a > 0) matrix_out[7-j] = matrix_out[7-j] + math.pow(2, i);
        }
    }
    
    return matrix_out;
}
 
function display_charset() { 
    local i = 0;
    local j = 0;
    local matrix_out = [0,0,0,0,0,0,0,0];
    
    // Run through each of the charset's characters, one by one
    for (j = 0 ; j < alpha_count ; j++) {
        // Rotate the character matrix to reflect the display orientation
        matrix_out = rotate_matrix(charset[j]);
        for (i = 1 ; i < 9 ; i++) {
            // Write each line of the character 8 x 8 matrix 
            // to the appropriate MAX7219 line-display register, 1 to 8
            write_LED(i, matrix_out[i-1]);
        }
        
        delay(1000);    // 1s delay between characters
    }		
}
 
function loop() {
    display_charset();
    imp.wakeup(2.0, loop);	// 2s delay between loop cycles
}
 
// Start point for the program
init_LED();     // Initialise the LED matrix
loop();         // Enter the program loop