Using an ATTiny85 to control a relay based on an LM34 temperature reading

The following code uses an ATTiny85 to turn a relay on and off based on a temperature reading from the LM34 temperature sensor. I used this to turn a freezer on and off to help save energy and to prevent the freezer from actually freezing anything.

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/* * LM34.c * * Created: 4/13/2015 10:35:05 PM * Author: Jacob */ #include <avr/io.h> #include <util/delay.h> #define relay PB1 //The relay is connected to PB1 on the ATTiny85 #define led PB0 //The indicator LED is connect to PB0 on the ATTiny85 void ledAlert() //Function used to blink the LED at a fast pulse, used for alerting user if there is an error with the cooling system { PORTB ^= (1 << led); //Toggle the LED _delay_ms(250); //LED state changes every 250 milliseconds } void initADC() { DDRB |= (1 << relay); //Sets the relay pin as an output DDRB |= (1 << led); //Sets the led pin as an output ADCSRA |= (1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0); //Setting a 1 to "ADEN" enables the ADC feature //Setting a 1 to "ADPS2, ADPS1, ADPS0" sets the pre-scaler to divide the clock by 128 ADMUX |= (0<<REFS0)|(0<<REFS1); //Reference = Vcc ADMUX |= (1<<ADLAR); //Left adjust ADC results ADMUX |= (1<<MUX1); //Select ADC3 (pin 2) ADMUX |= (1<<MUX0); //Select ADC3 (pin 2) ADCSRA |= (1 << ADATE); //Free running mode ADCSRB &= ~((1<<ADTS2)|(1<<ADTS1)|(1<<ADTS0)); //First three bits of ADCSRB needs to be 000 to select free running mode ADCSRA |= (1<<ADEN); //Completes the initialization of ADC ADCSRA |= (1<<ADSC); //Start ADC conversions } int main(void) { initADC(); //Initialize the registers so the ATTiny85 can perform Analog to Digital Conversions while(1) { if(ADCH > 19) //(19/255) * 5 = 39.2 degrees //If the temperature is above 39 degrees, Turn the relay and led on { PORTB |= (1 << relay); PORTB |= (1 << led); while(ADCH > 18); //35.3 //While the temperature is greater than 35 degrees, stay here to temporarily lock it in place } else //If the temperature is below 39 degrees, turn the relay off so the beer doesn't freeze { PORTB &= (0 << relay); //Turn relay off if the temperature is acceptable (below 38 degrees) PORTB &= (0 << led); //Turn led off if the temperature is acceptable (below 38 degrees) } } } /* 8 bit value to degrees F 15 -> 29.4 16 -> 31.3 17 -> 33.3 18 -> 35.3 19 -> 37.2 20 -> 39.2 21 -> 41.1 22 -> 43.1 23 -> 45.1 */

I don't have a wiring diagram or pictures to show as I no longer need this project. But this is a good example to show how to read an analog input into the ATTiny85 using the ADC.