DIY Hideout: How to make a custom DIY Temperature Meter using Bar Graph & Atmega328p

Video

In this post, I will show you how to make a custom DIY temperature meter using bar graph & Atmega328p

Below is the circuit diagram which was created in KiCAD for this project which includes parts like

1*Atmega328p
1*Bar Graph
1*10K Ohm
10*220 Ohm
1*LM35
1*Terminal Block
2*22pf Ceramic Capacitor
1*16 MHz Crystal
1*Custom Made PCB by JLCPCB.com

Theory

The main section of the circuit (Atmega328p, 22pF Ceramic Capacitor, 16MHz Crystal, 10K ohm) is the downsized version of the Arduino UNO

The input section of the circuit is an integrated analog temperature sensor whose electrical output is proportional to Degree Centigrade (LM35). The output of the LM35 is connected to pin 23 of the Atmega328p.

The output section is the remaining section of the circuit which includes Bar graph and 10*220 ohm resistor

Affiliate Links

Atmega328p

Amazon IND: https://amzn.to/2YOAyk2
Amazon US: https://amzn.to/2YLm18q
AliExpress: http://s.click.aliexpress.com/e/cpGPZBZI
Banggood: https://www.banggood.in/custlink/GvvmPYsIOI

Bar Graph

Amazon IND: https://amzn.to/2Ma64Hu
Amazon US: https://amzn.to/2Wlpayd
AliExpress: http://s.click.aliexpress.com/e/bgbq8NP2

16 MHz Crystal

Amazon IND: https://amzn.to/2VS266c
Amazon US: https://amzn.to/2Erg2hq
AliExpress: http://s.click.aliexpress.com/e/bpqjFRKC
Banggood: https://www.banggood.in/custlink/KvGDPEnZOB

Next, I created the PCB layout in KiCAD & ordered the PCB board through PCB fabricator JLCPCB.com

Next, I uploaded the below sketch to the Atmega328p

Read: How to upload the sketch to an Atmega328p

Sketch Start

float val;
float tempPin = A0;
int ledCount=10;
int thisLed;
int ledPin[] = {
3, 4, 5, 6, 7, 8, 9, 10, 11, 12
};
int ledON=HIGH;
int ledOFF=LOW;
void setup()
{
Serial.begin(9600);
for (int thisLed = 0; thisLed < ledCount; thisLed++) {
pinMode(ledPin[thisLed], OUTPUT);
}
}
void loop()
{
val = analogRead(tempPin);
float mv = ( val/1024.0)*5000;
float cel = mv/10;
float farh = (cel*9)/5 + 32;
if (cel >= 25 && cel < 26 ) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledOFF);
digitalWrite(ledPin[2], ledOFF);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 26 && cel < 27) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledOFF);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 27 && cel < 28) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 28 && cel < 29) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 29 && cel < 30) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 30 && cel < 31) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 31 && cel < 32) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 32 && cel < 33) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledON);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 33 && cel < 34) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledON);
digitalWrite(ledPin[8], ledON);
digitalWrite(ledPin[9], ledOFF);
} else if (cel >= 34) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledON);
digitalWrite(ledPin[8], ledON);
digitalWrite(ledPin[9], ledON);
} else if (cel < 25 ) {
digitalWrite(ledPin[0], ledOFF);
digitalWrite(ledPin[1], ledOFF);
digitalWrite(ledPin[2], ledOFF);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
}
Serial.print("TEMPRATURE = ");
Serial.print(cel);
Serial.print("*C");
Serial.println();
delay(1000);
/* uncomment this to get temperature in farenhite
Serial.print("TEMPRATURE = ");
Serial.print(farh);
Serial.print("*F");
Serial.println();
*/
}

Sketch End

Sketch Explanation

The below section of the sketch is where all the variables are declared and initialized

float val;
float tempPin = A0;
int ledCount=10;
int thisLed;
int ledPin[] = {
3, 4, 5, 6, 7, 8, 9, 10, 11, 12
};
int ledON=HIGH;
int ledOFF=LOW;
void setup()
{
Serial.begin(9600);
for (int thisLed = 0; thisLed < ledCount; thisLed++) {
pinMode(ledPin[thisLed], OUTPUT);
}
}

In this section of the sketch, the analog data is converted to the readable format

val = analogRead(tempPin); //to read the data from the LM35
float mv = ( val/1024.0)*5000; //Converting the input voltage to digital value (b/w the range 0 to 1023)
float cel = mv/10; //Converting to celcius
float farh = (cel*9)/5 + 32; //Converting to Fahrenheit

In the next section of the sketch, the converted value is passed through a number IF loop to determine how many LED lights should be turned ON

if (cel >= 25 && cel < 26 ) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledOFF);
digitalWrite(ledPin[2], ledOFF);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 26 && cel < 27) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledOFF);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 27 && cel < 28) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 28 && cel < 29) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 29 && cel < 30) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 30 && cel < 31) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 31 && cel < 32) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 32 && cel < 33) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledON);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
} else if(cel >= 33 && cel < 34) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledON);
digitalWrite(ledPin[8], ledON);
digitalWrite(ledPin[9], ledOFF);
} else if (cel >= 34) {
digitalWrite(ledPin[0], ledON);
digitalWrite(ledPin[1], ledON);
digitalWrite(ledPin[2], ledON);
digitalWrite(ledPin[3], ledON);
digitalWrite(ledPin[4], ledON);
digitalWrite(ledPin[5], ledON);
digitalWrite(ledPin[6], ledON);
digitalWrite(ledPin[7], ledON);
digitalWrite(ledPin[8], ledON);
digitalWrite(ledPin[9], ledON);
} else if (cel < 25 ) {
digitalWrite(ledPin[0], ledOFF);
digitalWrite(ledPin[1], ledOFF);
digitalWrite(ledPin[2], ledOFF);
digitalWrite(ledPin[3], ledOFF);
digitalWrite(ledPin[4], ledOFF);
digitalWrite(ledPin[5], ledOFF);
digitalWrite(ledPin[6], ledOFF);
digitalWrite(ledPin[7], ledOFF);
digitalWrite(ledPin[8], ledOFF);
digitalWrite(ledPin[9], ledOFF);
}

The next section of the sketch is optional. This section is to see the temperature in the built-in serial monitor of the Arduino IDE

Serial.print("TEMPRATURE = ");
Serial.print(cel);
Serial.print("*C");
Serial.println();
delay(1000);
/* uncomment this to get temperature in farenhite
Serial.print("TEMPRATURE = ");
Serial.print(farh);
Serial.print("*F");
Serial.println();
*/
}