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ATTiny85 3 channel software PWM to drive RGB LED
// based largely on Atmel's AVR136: Low-Jitter Multi-Channel Software PWM Application Note:
// http://www.atmel.com/dyn/resources/prod_documents/doc8020.pdf
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#define CHMAX 3 // maximum number of PWM channels
#define PWMDEFAULT 0x00 // default PWM value at start up for all channels
#define RED_CLEAR (pinlevelB &= ~(1 << RED)) // map RED to PB0
#define GREEN_CLEAR (pinlevelB &= ~(1 << GREEN)) // map GREEN to PB1
#define BLUE_CLEAR (pinlevelB &= ~(1 << BLUE)) // map BLUE to PB2
//! Set bits corresponding to pin usage above
#define PORTB_MASK (1 << PB0)|(1 << PB1)|(1 << PB2)
#define set(x) |= (1<<x)
#define clr(x) &=~(1<<x)
#define inv(x) ^=(1<<x)
#define RED PB0
#define GREEN PB1
#define BLUE PB2
#define LED_PORT PORTB
#define LED_DDR DDRB
void delay_ms(uint16_t ms);
void init();
unsigned char compare[CHMAX];
volatile unsigned char compbuff[CHMAX];
int r_val = 0x00;
int g_val = 0x55;
int b_val = 0xAA;
float dim = 1;
int main() {
init();
int r_dir = 1;
int g_dir = 2;
int b_dir = 4;
for(;;) {
if (r_val > 254 - 1) {
r_dir = -1;
}
if (r_val < 1 + 1) {
r_dir = 1;
}
if (g_val > 254 - 3) {
g_dir = -2;
}
if (g_val < 1 + 3) {
g_dir = 2;
}
if (b_val > 254 - 4) {
b_dir = -4;
}
if (b_val < 1 + 4) {
b_dir = 4;
}
r_val += r_dir;
g_val += g_dir;
b_val += b_dir;
compbuff[0] = r_val;
compbuff[1] = g_val;
compbuff[2] = b_val;
delay_ms(50);
}
}
void delay_ms(uint16_t ms) {
while (ms) {
_delay_ms(1);
ms--;
}
}
void init(void) {
// set the direction of the ports
LED_DDR set(RED);
LED_DDR set(GREEN);
LED_DDR set(BLUE);
unsigned char i, pwm;
CLKPR = (1 << CLKPCE); // enable clock prescaler update
CLKPR = 0; // set clock to maximum (= crystal)
pwm = PWMDEFAULT;
// initialise all channels
for(i=0 ; i<CHMAX ; i++) {
compare[i] = pwm; // set default PWM values
compbuff[i] = pwm; // set default PWM values
}
TIFR = (1 << TOV0); // clear interrupt flag
TIMSK = (1 << TOIE0); // enable overflow interrupt
TCCR0B = (1 << CS00); // start timer, no prescale
sei();
}
ISR (TIM0_OVF_vect) {
static unsigned char pinlevelB=PORTB_MASK;
static unsigned char softcount=0xFF;
PORTB = pinlevelB; // update outputs
if(++softcount == 0){ // increment modulo 256 counter and update
// the compare values only when counter = 0.
compare[0] = compbuff[0]; // verbose code for speed
compare[1] = compbuff[1];
compare[2] = compbuff[2];
pinlevelB = PORTB_MASK; // set all port pins high
}
// clear port pin on compare match (executed on next interrupt)
if(compare[0] == softcount) RED_CLEAR;
if(compare[1] == softcount) GREEN_CLEAR;
if(compare[2] == softcount) BLUE_CLEAR;
}
@midastsai

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@midastsai midastsai commented May 20, 2013

Hi, I tried to run the program in the ATtiny85. It's WORK. But I want to add a sensor through the analogRead, Unfortunately it isn't WORK. Whether the sofeware PWM and analogread not be used simultaneously?
Can you help me to give some advice? Thanks.

@peterrus

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@peterrus peterrus commented May 23, 2013

Isn't analogRead() a function part of Arduino?

@geneg

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@geneg geneg commented Jul 2, 2013

Thanks!!!
the code works smooth even on ATtiny13 with little changes
TIFR to TIFR0
and TIMSK to TIMSK0

@JoaquinEduardoArreguez

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@JoaquinEduardoArreguez JoaquinEduardoArreguez commented Oct 31, 2015

Hey! nice code, but i have a question: f_cpu is not defined for delay, haven't read all the code, but, is it clock-freq dependant? (sry about my english, I'm from Argentina!)

@tmk88

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@tmk88 tmk88 commented Mar 24, 2016

Hi, the code works, but how can I show only the basic colors (red, blue, green) alone?

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