====== DMX dimmer ====== ~~META:description abstract=A DMX512 2 channels dimmer~~ A DMX512 2 channels dimmer. ===== Features ===== * Up to 4A, can drive halogen bulbs * Uses 2 DMX channels ===== Theory of dimming ===== Bulb voltage from trigger time t to end of period is U(t) = U_eff sqrt{1-{t/10ms}+{sin({2 pi t}/10ms)/{2 pi}}} Power is P(t) = {U(t)^2} / Z Power over full wave is P(0) = U_eff^2 / Z and power for value is P(n) = {n / 255} P(0) Using a quick and dirty solver we find the trigger time for each value (in us) :

C array version :


const uint16_t timings[256] = {
	9331, 9031, 8848, 8709, 8593, 8493, 8403, 8322,
	8248, 8179, 8114, 8053, 7995, 7940, 7887, 7836,
	7788, 7741, 7695, 7651, 7609, 7567, 7527, 7487,
	7449, 7411, 7375, 7339, 7303, 7269, 7235, 7202,
	7169, 7137, 7105, 7074, 7043, 7013, 6983, 6953,
	6924, 6895, 6867, 6839, 6811, 6783, 6756, 6729,
	6703, 6676, 6650, 6624, 6599, 6573, 6548, 6523,
	6498, 6474, 6449, 6425, 6401, 6377, 6354, 6330,
	6307, 6283, 6260, 6237, 6215, 6192, 6169, 6147,
	6124, 6102, 6080, 6058, 6036, 6015, 5993, 5971,
	5950, 5928, 5907, 5886, 5865, 5843, 5822, 5802,
	5781, 5760, 5739, 5718, 5698, 5677, 5657, 5636,
	5616, 5596, 5575, 5555, 5535, 5515, 5495, 5475,
	5455, 5435, 5415, 5395, 5375, 5355, 5335, 5315,
	5295, 5276, 5256, 5236, 5217, 5197, 5177, 5157,
	5138, 5118, 5099, 5079, 5059, 5040, 5020, 5000,
	4981, 4961, 4942, 4922, 4902, 4883, 4863, 4844,
	4824, 4804, 4784, 4765, 4745, 4725, 4706, 4686,
	4666, 4646, 4626, 4606, 4586, 4566, 4546, 4526,
	4506, 4486, 4466, 4446, 4426, 4405, 4385, 4365,
	4344, 4324, 4303, 4283, 4262, 4241, 4220, 4199,
	4179, 4158, 4136, 4115, 4094, 4073, 4051, 4030,
	4008, 3986, 3965, 3943, 3921, 3899, 3877, 3854,
	3832, 3809, 3786, 3764, 3741, 3718, 3694, 3671,
	3647, 3624, 3600, 3576, 3552, 3527, 3503, 3478,
	3453, 3428, 3402, 3377, 3351, 3325, 3298, 3272,
	3245, 3218, 3190, 3162, 3134, 3106, 3077, 3048,
	3018, 2988, 2958, 2927, 2896, 2864, 2832, 2799,
	2766, 2732, 2698, 2662, 2626, 2590, 2552, 2514,
	2474, 2434, 2392, 2350, 2306, 2260, 2213, 2165,
	2114, 2061, 2006, 1948, 1887, 1822, 1753, 1679,
	1598, 1508, 1408, 1292, 1153, 970, 670, 0
};

The solver :


var nl = {};

for(var t=0; t<=0.01; t+= 0.000001) {
  var at = 1 - t/0.01 + Math.sin(2 * Math.PI * t / 0.01) / (2 * Math.PI);
  var n = Math.round(255 * at);
  if(typeof nl['_' + n] == 'undefined') nl['_' + n] = Math.round(1000000 * t);
}

var s = [];
for(var i=0; i<256; i++) s.push(i + ';' + nl['_' + i]);

console.log(s.join("\n"));

Analysis file with charts comparing linear approach with fitted one : {{:projects:dmx_dimmer:timings.xls}} ===== Electronics ===== {{schematic>schematic.svg}} ===== Source code ===== DMX to power conversion is done through a 16 bit timer with a prescaler of 8 for a clock of 8MHz. This allows for approx. 10k steps over a single mains half period (zero-crossing sensor time delta should be taken into account here). Sensor accuracy can be improved by detecting falling edge, reseting timer, then detecting rising edge and adding 1/2 of measured delay after further falling edges by offsetting OCR1x. /** * @defgroup DMX512 dimmer * @type firmware * @file main.c * @author Etienne Meleard * @creation 2014-06-20 * @tabsize 4 * @mcu ATMEGA8L * @fcpu 8MHz */ //============================ WARNING ===============================// //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!// // // // Fuses must be like SUT1 = 1, SUT0 = 1, CKSEL3 = 1, CKSEL2 = 0, // // CKSEL1 = 0 and CKSEL0 = 0 to ensure using the crystal as clock // // (otherwise it uses the 8MHz internal clock), full swing mode is // // mandatory to acheive 8MHz operation. // // // // CKDIV8 fuse must not be set to avoid clock frequency divided by 8 // // // // Fuse set or = 1 means checked in ponyprog // // // //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!// //====================================================================// // ================= Fuses ================= // /*FUSES = { // No success writing fuse this way, command line below ... .low = (FUSE_SUT1 & FUSE_SUT0 & FUSE_CKSEL3), .high = HFUSE_DEFAULT, .extended = EFUSE_DEFAULT, };*/ // Run avrdude -c usbasp -p m8 -U lfuse:w:0xc7:m -U hfuse:w:0xdf:m at // first (-F may be needed) // ================ Includes =============== // #include #include #include #include #include // ================ Pinouts ================ // #define LED Bit(PORTD).bit5 #define RX Bit(PORTD).bit0 #define RX_COMPLETE SIG_USART_RECV #define RX_INT Bit(PORTD).bit2 #define RX_SIG SIG_INTERRUPT0 #define RX_TIMER TCNT0 #define BREAK_LEN 11 #define MAB_LEN 1 #define DIP_0 Bit(PINC).bit0 #define DIP_1 Bit(PINC).bit1 #define DIP_2 Bit(PINC).bit2 #define DIP_3 Bit(PINC).bit3 #define DIP_A Bit(PORTC).bit4 #define DIP_B Bit(PORTB).bit4 #define DIP_C Bit(PORTB).bit5 #define EXT_ADC 6 #define EXT_INPUT Bit(PIND).bit3 #define EXT_OUTPUT Bit(PORTD).bit3 #define EXT_SIG SIG_INTERRUPT1 #define OUT_1 Bit(PORTB).bit1 #define CH_1 OCR1A #define OUT_2 Bit(PORTB).bit2 #define CH_2 OCR1B // ================ Macros ================= // #define BLINK LED=1; _delay_ms(150); BLINK LED=0; _delay_ms(150) #define RX_START UCSRB |= 0x10 #define RX_STOP UCSRB &= 0xef #define ADDR_4 PINC & 0x0f // ================ Globals ================ // volatile uint16_t address = 0x0000; volatile uint16_t received = 0; const uint16_t timings[256] = PROGMEM { 9331, 9031, 8848, 8709, 8593, 8493, 8403, 8322, 8248, 8179, 8114, 8053, 7995, 7940, 7887, 7836, 7788, 7741, 7695, 7651, 7609, 7567, 7527, 7487, 7449, 7411, 7375, 7339, 7303, 7269, 7235, 7202, 7169, 7137, 7105, 7074, 7043, 7013, 6983, 6953, 6924, 6895, 6867, 6839, 6811, 6783, 6756, 6729, 6703, 6676, 6650, 6624, 6599, 6573, 6548, 6523, 6498, 6474, 6449, 6425, 6401, 6377, 6354, 6330, 6307, 6283, 6260, 6237, 6215, 6192, 6169, 6147, 6124, 6102, 6080, 6058, 6036, 6015, 5993, 5971, 5950, 5928, 5907, 5886, 5865, 5843, 5822, 5802, 5781, 5760, 5739, 5718, 5698, 5677, 5657, 5636, 5616, 5596, 5575, 5555, 5535, 5515, 5495, 5475, 5455, 5435, 5415, 5395, 5375, 5355, 5335, 5315, 5295, 5276, 5256, 5236, 5217, 5197, 5177, 5157, 5138, 5118, 5099, 5079, 5059, 5040, 5020, 5000, 4981, 4961, 4942, 4922, 4902, 4883, 4863, 4844, 4824, 4804, 4784, 4765, 4745, 4725, 4706, 4686, 4666, 4646, 4626, 4606, 4586, 4566, 4546, 4526, 4506, 4486, 4466, 4446, 4426, 4405, 4385, 4365, 4344, 4324, 4303, 4283, 4262, 4241, 4220, 4199, 4179, 4158, 4136, 4115, 4094, 4073, 4051, 4030, 4008, 3986, 3965, 3943, 3921, 3899, 3877, 3854, 3832, 3809, 3786, 3764, 3741, 3718, 3694, 3671, 3647, 3624, 3600, 3576, 3552, 3527, 3503, 3478, 3453, 3428, 3402, 3377, 3351, 3325, 3298, 3272, 3245, 3218, 3190, 3162, 3134, 3106, 3077, 3048, 3018, 2988, 2958, 2927, 2896, 2864, 2832, 2799, 2766, 2732, 2698, 2662, 2626, 2590, 2552, 2514, 2474, 2434, 2392, 2350, 2306, 2260, 2213, 2165, 2114, 2061, 2006, 1948, 1887, 1822, 1753, 1679, 1598, 1508, 1408, 1292, 1153, 970, 670, 0 }; // ================ Functions ============== // uint16_t getTiming(uint8_t value) { return pgm_read_byte(&timings[255 - value]); // Opposite offset required to emulate going-down PWM slope } void init(void) { // Led as output DDRD |= 1 << 5; // USART UCSRA = 0x00; // No doubling of frequency UCSRB = 0x80; // Rx disabled, Rx irq enabled, 8bit mode UCSRC = 0x8e; // Async, no parity, 2 stops, 8 bits UBRR = 103; // 250kbds // Detection timer (timer 0) TCCR0 = 0x03; // 64 prescaler, increment every 8us // Dip inputs DDRC &= 0xf0; // Dip outputs DDRC |= 0x10; DDRB |= 0x30; DIP_A = 0; DIP_B = 0; DIP_C = 0; // Channels timer (timer 1) TCCR1A = 0x82; // 16 bits, fast, inverting PWM on OC1A and OC1B TCCR1B = 0x1a; // with 8 prescaler ~ 1MHz tick period ICR1 = 0xffff; // Timer max to 65535 CH_1 = getTiming(0); // Channel 1 to 0 CH_2 = getTiming(0); // Channel 2 to 0 // B timer (timer 2) TCCR2 = 0x6e; // 8 bits, fast, non-inverting PWM on OC2 BLUE_CH = 0x00; // Blue channel to 0 } void getAddress(void) { uint16_t buffer = 0x0000; DIP_C = 1; buffer += ADDR_4; DIP_C = 0; buffer <<= 4; DIP_B = 1; buffer += ADDR_4; DIP_B = 0; buffer <<= 4; DIP_A = 1; buffer += ADDR_4; DIP_A = 0; address = buffer; } uint8_t getFrameStart(void) { while(RX); RX_TIMER = 0; while(!RX && RX_TIMER < BREAK_LEN); if(RX_TIMER < BREAK_LEN) return 0; // Error, break too short RX_STOP; RX_TIMER = 0; while(RX && RX_TIMER < MAB_LEN); if(RX_TIMER < MAB_LEN) return 0; // Error, break too short RX_START; received = 0; return 1; } // =============== Interrupts ============== // SIGNAL(RX_COMPLETE) { if(!received && UDR) { // First slot is not 0x00, not a setting packet RX_STOP; return; } if(received < address + 1) return; // Address not reached if(received > address + 2) { // Received enough packets, stop receiving and wait for next frame RX_STOP; return; } // Got channel, set it switch(received - (address + 1)) { case 0: CH_1 = UDR; break; case 1: CH_2 = UDR; break; } received++; } // ================== Main ================= // int main(void) { uint16_t time_without_start = 0; cli(); // WatchDog disabled AT ALL TIMES ! init(); sei(); BLINK; BLINK; getAddress(); while(1) { if(getFrameStart()) { LED = 0; time_without_start = 0; } _delay_us(100); time_without_start++; if(time_without_start > 10000) { // 1s without start LED = 1; // Error } } return 0; } ===== How to ===== ===== Manual ===== {{tag>microcontroller lighting dmx}}