{"id":102,"date":"2012-10-29T17:20:31","date_gmt":"2012-10-29T23:20:31","guid":{"rendered":"http:\/\/www.teracharge.com\/?p=102"},"modified":"2013-01-06T16:19:21","modified_gmt":"2013-01-06T23:19:21","slug":"halloween-leds","status":"publish","type":"post","link":"http:\/\/www.teracharge.com\/?p=102","title":{"rendered":"Halloween LEDs"},"content":{"rendered":"

There comes a time in a mouse\u2019s life when it is no longer a mouse: it transpires away from the realm of the living and joins the ever increasing pile of electronics junk.<\/p>\n

My mouse, computer mouse that is, gave its last breath not too long ago.\u00a0 In the midst of an intense Portal2 Co-Op session, my mouse suddenly decided that it would no longer acknowledge any my clicks, irrespective of how hard I pressed the buttons.\u00a0 Thankfully, spare mice are plentiful in these parts, and it wasn’t long until the Portal2 endeavor vigorously ensued.<\/p>\n

I suppose that in normal circumstances I should have felt at least a bit sad about my loss, but instead I couldn\u2019t wait to open it up and figure out the decorative multi-color LED was wired (this video<\/a> illustrates this feature).<\/p>\n

After cracking the mouse open, I was surprised to find that the LED only had two leads instead of the standard four.\u00a0 Aha!\u00a0 This is one of those integrated LEDs: and sure enough, wiring straight to 5V produced the ever changing color patterns.\u00a0 Very simple to wire up, entertaining to watch, but not terribly useful to keep around: unless of course Halloween is around the corner.<\/p>\n

Carve a pumpkin (there\u2019s a great online tutorial<\/a> on how to carve amazing looking pumpkins), wire up the LED, and you got yourself a groovy jack-o-lantern.<\/p>\n

\"Integrated<\/a>

Integrated RGB LED wired to a 5V boost circuit from Sparkfun and batteries.<\/p><\/div>\n

\"Carving<\/a>

Carving a Pumpkin.<\/p><\/div>\n

\"Integrated<\/a>

Integrated RGB LED circuit inside the pumpkin.<\/p><\/div>\n

Mission accomplished, unless, of course, you have two carved pumpkins.\u00a0 It simply wouldn\u2019t be fair for the other pumpkin to not have any cool LEDs as well.\u00a0 The second pumpkin, carved by my lovely assistant, is pretty evil looking.\u00a0 Groovy LEDs don’t go well with evil pumpkins, but it’s nothing a small PIC and a few spare LEDs can\u2019t fix.<\/p>\n

\"Evil<\/a>

Evil pumpkin, and friend.<\/p><\/div>\n

For this project, you\u2019ll need:<\/p>\n

    \n
  1. A small breadboard (something like this<\/a> would do)<\/li>\n
  2. A 0.1uF ceramic capacitor.<\/li>\n
  3. A 4.7k-10kOhm resistor.<\/li>\n
  4. Five 220Ohm resistors.<\/li>\n
  5. Five LEDs of your choice (preferably of different colors).<\/li>\n
  6. A 3.3V or 5V boost converter (Sparkfun<\/a> builds a great little boost converter)<\/li>\n<\/ol>\n

    Wire them up like this:<\/p>\n

    \"Halloween<\/a>

    Halloween LED Schematic<\/p><\/div>\n

    And with the little snippet of code below, you got yourself a pretty angry multi-colored LED pattern.<\/p>\n

    \r\n\/* \r\n * File:   main.c\r\n * Author: Jonathan Bruneau\r\n *\r\n * Created on October 26, 2012, 10:52 AM\r\n *\/\r\n\r\n#pragma config FOSC = IRC  \t\/\/Internal RC oscillator\r\n#pragma config MCLRE = ON       \/\/MCLR is enabled to allow for ISCP.\r\n#pragma config LVP = OFF\t\/\/Single Supply ISCP disabled.\r\n#pragma config STVREN = ON\t\/\/Stack overflow will cause a reset.\r\n#pragma config XINST = OFF\t\/\/Extended instruction set disabled.\r\n\r\n#include \"xc.h\"\r\n#include \"stdlib.h\"\r\n#include \"stdint.h\"\r\n\r\n\/\/The port mask for blink LEDs\r\n#define PORT_MASK 0x1F\r\n\r\n\/\/Set the timer to the specified elapsed time.\r\n#define set_timer(x) do{TMR0L = (uint8_t)x;}while(0)\r\n\r\n\/\/Turn the LEDs on\/off in function of the specified value.\r\n#define set_leds(x) do{LATC = (LATC & ~PORT_MASK) | ((x) & PORT_MASK);}while(0)\r\n\r\nvoid interrupt high_isr(void)\r\n{\r\n    \/\/Clear timer interrupt.\r\n    INTCONbits.TMR0IF = 0;\r\n\r\n    {\r\n        \/\/Generate random value once, and use said value to set the timer and the LEDs.\r\n        const uint16_t x = rand();\r\n        set_timer(x);\r\n        set_leds(x);\r\n    }\r\n}\r\n\r\nint main(int argc, char** argv)\r\n{\r\n    \/\/Set the oscillator to a *really* slow speed to save on power.\r\n    OSCTUNEbits.INTSRC = 0;\r\n    OSCCONbits.IRCF = 0x0;\r\n\r\n    \/\/Seed the random value generator.\r\n    srand(0);\r\n\r\n    \/\/Make the processor go to IDLE when a sleep command is received.\r\n    \/\/(This allows Timer0 to continue operation).\r\n    OSCCONbits.IDLEN = 1;\r\n\r\n    \/\/Set PORT C0, C1, C2, C3, and C4 to outputs.\r\n    TRISC &= ~PORT_MASK;\r\n\r\n    \/\/Setup Timer\r\n    T0CONbits.T0CS = 0;     \/\/Use internal oscillator as clock source.\r\n    \/\/T0CONbits.T0PS = 0x5;   \/\/1:32 prescaler.  Increase the prescaler if it's the holidays.\r\n    \/\/T0CONbits.PSA = 0;      \/\/Use prescaler.\r\n    INTCONbits.TMR0IE = 1;  \/\/Enable timer0 interrupts.\r\n\r\n    set_timer(rand());      \/\/Set the timer to an initial value.\r\n    T0CONbits.TMR0ON = 1;   \/\/Enable the timer.\r\n\r\n    \/\/Enable global interrupts.\r\n    INTCONbits.GIEL = INTCONbits.GIEH = 1;\r\n\r\n    while(1)\r\n        Sleep();\r\n}\r\n<\/pre>\n
    \"Multi-Color<\/a>
    Multi-Color LED breadboard for evil pumpkin.<\/p><\/div>\n
    What the code does, in essence, is initialize Timer0 of the PIC18 to a random value, and starts the timer.\u00a0 On every timer interrupt, a random value is assigned to the LEDs (wired to PORTC0 to PORTC4), and a new random value is assigned to the timer.\u00a0 The LEDs thus turn on\/off randomly, and at a random intervals.\u00a0 The end effect is pretty cool, to say the least.\u00a0 But don’t take my word for it: check it this video that show both pumpkins in action.<\/p>\n