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Help: Temperature controller with ATTINY85 and LM35


Hello everybody,

I designed a circuit which reads a LM35 temperature sensor, blinks 2 LED and turns on and off a Fan over a MOSFET. However, it does not function as I want it to do. Here is the schematic and the code (LED colors are different in the original circuit but it does not matter)


#define analogPin 3 // Data cable connected to the analog pin
#define YelPin 1 // yellow LED pin for Temp>35
#define RedPin 0 //red LED pin for Temp>39
#define FanPin 2 //Fan connected to the MOSFET will be high Temp>35
int val=0; // variable to store the value of temperature reading

void setup(){
pinMode(YelPin, OUTPUT);
pinMode(RedPin, OUTPUT);
pinMode(FanPin, OUTPUT);
function0(); // for the temperatures out of the interested range
function1(); //for the temperatures lower than 39 and higher than 36
function2(); //for the temperatures higher than 39


void loop(){
val = analogRead(analogPin)*0.48828125; //conversation of the analog reading to the centigrade
if(val<35 && val>60){
if(val>=35 && val<39){
if(val>39 && val<60){

void function0(){ //function which should work only when the temperature is out of interested range
digitalWrite(YelPin, LOW);
digitalWrite(RedPin, LOW);
delay (2000);

void function1(){ //function which should work only in 35-39 degrees
digitalWrite(YelPin, HIGH);
delay (2000);

void function2(){ //funtion which should work only after 39 degrees
digitalWrite(YelPin, LOW);

The circuit was programmed with an Arduino Uno as ISP and the clock frequency is 8MHz
When I power up the circuit, It waits for a while, then turns the Yellow LED on as well as the fan for half a second and turns off. If I heat the sensor further, it turns the red LED on as well as the fan and stays on half a second as the previous case and waits and does the same....

What I want to have
Read the temperature,
if temperature <36 and > 60 do nothing
if temperature >36 and < 39 turn the yellow LED as well as the fan on
if temperature > 39 and <60 turn the red LED as well as the fan on

What am I doing wrong here?

Last edited:

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