| /******************************************************************************* Rue's "is it alive" program for avr processors also makes a good skel to build your programs form ;) 16Mhz Red LED with clear lens. *******************************************************************************/ /* 1 PB0 <- led 2 PB1 3 PB2 <- led 4 PB3 5 PB4 6 PB5 7 PB6 8 PB7 9 PA0 10 PA1 11 PA2 12 PA3 13 PA4 14 PA5 15 PA6 16 PA7 17 PC7 18 PC6 19 PC5 20 PC4 21 PC3 22 PC2 23 PC1 24 PC0 25 PD7 26 PD2 27 PD3 28 PD4 29 PD5 30 PD6 This example shows one way of using an LED as a light sensor. You will need to wire it up like this: + port B0 | < > 470 ohm resistor < | | ----- / \ 5mm red led with a clear lens ----- | | + port B2 What we are going to do is apply a positive voltage at port B0 and a low voltage at port B2. This is backwards for the LED, current will not flow and it will not light, but we will charge up the capacitance of the LED junction. Then we are going to disconnect the output drivers from PORT B0 and count how long it takes to discharge. The brighter the light, the lower the capacitance and the faster is will lose its charge. The rest of this app here will watch the led and toggle its on/off state when it sees a 'dark happen' :) */ #include <avr/io.h> // misc #define SetBit(BIT, PORT) PORT |= (1<<BIT) #define ClearBit(BIT, PORT) PORT &= ~(1<<BIT) #define IsHigh(BIT, PORT) (PORT & (1<<BIT)) != 0 #define IsLow(BIT, PORT) (PORT & (1<<BIT)) == 0 #define NOP() asm volatile ("nop"::) #define OUTPUT 1 #define INPUT 0 #define HIGH 1 #define LOW 0 #define LED_CATHODE 2 #define LED_ANODE 0 #define LED_PORT PORTB #define LED_DDR DDRB #define LED_INPUT PINB // this determines a 'light level cutoff' if it sees less than 3000 units // it gives up. this mixes with the contrast delay you will read about later #define JMAX 3000 void Delay(int delay); void Delay2(int delay); int readLED( char onoff ); int main (void) { unsigned int val; char oncount, onoff; // set up directions DDRA = (INPUT << PA0 | INPUT << PA1 |INPUT << PA2 |INPUT << PA3 |INPUT << PA4 |INPUT << PA5 |INPUT << PA6 |INPUT << PA7); DDRB = (OUTPUT << PB0 | OUTPUT << PB1 |OUTPUT << PB2 |OUTPUT << PB3 |OUTPUT << PB4 |OUTPUT << PB5 |OUTPUT << PB6 |OUTPUT << PB7); DDRC = (INPUT << PC0 | INPUT << PC1 |INPUT << PC2 |INPUT << PC3 |INPUT << PC4 |INPUT << PC5 |INPUT << PC6 |INPUT << PC7); DDRD = (INPUT << PD0 | INPUT << PD1 |INPUT << PD2 |INPUT << PD3 |INPUT << PD4 |INPUT << PD5 |INPUT << PD6 |INPUT << PD7); onoff = 0; oncount = 0; val = 0; while (1) { if (val < 600) // light level for us to decide to switch, depends on contrast delay oncount++; else oncount = 0; // 4 counts before we toggle if (oncount == 2) { if (onoff) onoff = 0; else onoff = 1; } val = readLED(onoff); // leave it like that for a bit before we do the next reading. Delay(15000); } } void Delay(int delay) { int x; for (x = delay; x != 0; x--) { asm volatile ("nop"::); } } void Delay2(int delay) { int x; for (x = delay; x != 0; x--) { Delay(65000); } } int readLED(char onoff) { unsigned int j; // Apply reverse voltage, charge up the pin and led capacitance SetBit(LED_CATHODE, LED_DDR ); // OUTPUT SetBit(LED_ANODE, LED_DDR ); // OUTPUT SetBit(LED_CATHODE, LED_PORT); // HIGH ClearBit(LED_ANODE, LED_PORT); // LOW Delay(5); // Isolate the cathode of the LED ClearBit(LED_CATHODE, LED_DDR); // INPUT ClearBit(LED_CATHODE, LED_PORT); // turn off internal pull-up resistor // Count how long it takes the led to discharge to a logic zero // this can take almost like 1/4 second! // In the dark j is lower and takes longer. for ( j = JMAX; ((j) && (IsHigh(LED_CATHODE, LED_INPUT))); j--) Delay(45); // this delay controls contrast // leave the led on if they wanted it like that if (onoff != 0) { SetBit(LED_ANODE, LED_PORT); // anode high ClearBit(LED_CATHODE, LED_PORT); // cathode low SetBit(LED_ANODE, LED_DDR); // output SetBit(LED_CATHODE, LED_DDR); // output } // return the brightness value return j; } // find me if you want to know how to read 8 leds with 9 io pins. :) |