Analog Read


Being able to read values other than 0 or 1 can come in handy!

Here I am using the Attiny84 along with a 10K potentiometer. The two ends of the potentiometer are attached to GND and VCC and the middle pin is going to PA1 (ADC1). I have PA0, the ADC reference voltage pin I selected, connected to 5V. I have an LED on PB1 to display the treshold being crossed. I am running the microchip at 8MHz.

 * Attiny84 analog read.c
 * Created: 19/01/28 2:20:06 PM
 * Author : marrs
#define F_CPU 8000000

#include <avr/io.h>
#include <util/delay.h>

int main(void)
	ADMUX |= (1 << REFS0); // PA0 ref voltage
	ADMUX = (0b11110000 & ADMUX) | PA1; // PA1 input select
	ADCSRA |= (1 << ADPS2) | (1 << ADPS0); // set clock to 32 divisions for 8MHz
	ADCSRA |= (1 << ADEN); /* enable ADC */

	uint16_t adcValue; //16 bit variable because the ADC on the Attiny84 is 10 bits.
	DDRB = 0b00000001; //LED on PB0

    while (1)
	ADCSRA |= (1 << ADSC); /* start conversion */
	_delay_ms(1); //instead of waiting for ready flag
	adcValue = ADC; /* store high byte into adcValue */

	if (adcValue > 200)
		PORTB = 0b00000001;
		PORTB = 0b00000000;

The only tricky part here for me (being a C newb!) was storing just the high byte of the ADC and understanding the size of data types relative to what is being stored inside of them. I couldn’t manage to read just ADCH or ADCL

Elliot Williams' Make: AVR Programming came in handy for this project.

The result (the analog value from the potentiometer is in yellow, the green LED which is triggered is in green):