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Controlling PWM With Potentiometer On AtMega328p

This is crude, but the thing works.  We’ve all seen this on the Great Scott Youtube channel (among other places) where a potentiometer controls the duty cycle of a PWM waveform on an oscilloscope.  This version isn’t pretty.  It needs some sanding and painting.  However, it’ll get a person started.  I’m adding it here as my personal library to steal from as needed.  Feel free to do the same.

Most of it is also stolen/borrowed from two main sources.

  1.  AVR Programming book by Make  (p.135)
  2.   AVRFreaks.net forum post 

Hardware Requirements

PC0 is looking for an input voltage ( keep it under 5V!!!!).  I made a voltage divider with a 10k resistor and a 10k pot using the AtMega’s 5V supply.  This will max out at 2.5V so I’m definitely throwing resolution away.

AREF needs 5V, too.  I tossed a random cap across it any GND to reduce some of the nasties.

#include <avr/io.h>
#include <util/delay.h>
#include "pinDefines.h"
#include "USART.h"

static inline void initADC0(void) {
	ADMUX |= (1 << REFS0);  // reference voltage
	ADCSRA |= (1 << ADPS1) | (1 << ADPS0); // ADC clock prescaler /8
	ADCSRA |= (1 << ADEN); // enable ADC } uint16_t divider = 1; void Duty( uint8_t percentage, uint16_t ICR1_value) { percentage = (percentage > 100 ? 100 : (percentage < 0 ? 0 : percentage)); uint16_t OCR = (uint16_t)(((uint32_t)percentage * (uint32_t)ICR1_value)/100) ; // Set pwm percent of pwm period OCR1AH = OCR >> 8;
OCR1AL = OCR & 0xFF;
}

void FrequencyPWM(uint16_t frequency, uint8_t percentage)
{
uint16_t TOP = F_CPU/(divider*frequency) - 1;
ICR1H = TOP >> 8;
ICR1L = TOP & 0xFF;
Duty(percentage, TOP);
}

void PWM1_INIT()
{
DDRB |= (1 << PINB1);
//DDRB |= (1 << PINB2);
// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: 62.500 kHz - I changed this to No prescailing using CS12=0, CS11=0, and CS10 = 1
// Mode: Fast PWM top=ICR1
// OC1A output: Non-Inverted PWM
// OC1B output: Non-Inverted PWM
// Noise Canceler: Off
// Input Capture on Falling Edge
// Timer Period: 1 s
// Output Pulse(s):
// OC1A Period: 1 s Width: 0.2 s
// OC1B Period: 1 s Width: 0.40001 s
// Timer1 Overflow Interrupt: Off
// Input Capture Interrupt: Off
// Compare A Match Interrupt: Off
// Compare B Match Interrupt: Off
TCCR1A=(1<<COM1A1) | (0<<COM1A0) | (0<<COM1B1) | (0<<COM1B0) | (1<<WGM11) | (0<<WGM10);
TCCR1B=(0<<ICNC1) | (0<<ICES1) | (1<<WGM13) | (1<<WGM12) | (0<<CS12) | (0<<CS11) | (1<<CS10);
TCNT1H=0x00;
TCNT1L=0x00;

FrequencyPWM(50, 10);
}

int main(void){
	
	PWM1_INIT();
		
	// Inits
	uint16_t adcValue;
	//uint8_t i;
	initADC0();
	initUSART();
	printString("Hello!\r\n");
	
	FrequencyPWM(10000, 50);
	_delay_ms(100);
	
	while(1){
		ADCSRA |= (1 << ADSC);  // start ADC conversion
		loop_until_bit_is_clear(ADCSRA, ADSC);  // wait until finished
		adcValue = ADC; // Read ADC in
		_delay_ms(50);
		transmitByte(adcValue);
		//_delay_ms(1000);
		
		uint8_t scaled_ADC = adcValue / 3;
		FrequencyPWM(10000, scaled_ADC);   // ( frequency , duty cycle % )	
	}	
}
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