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Introduction 
Published date: 18/6/2017
In this guide I will show you how to make your own Arduino  digital thermometer by using the DHT-22 sensor and Arduino Pro Mini board. It can be powered up from any USB power source and it can report the max and min values for temperature and humidity as it works.
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​In this guide you will also find the .stl files of the 3d printed case/box. 
The DHT-22 (also named as AM2302) is a digital-output relative humidity and temperature sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and spits out a digital signal on the data pin.

The DHT22 is a basic, low-cost digital temperature and humidity sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and spits out a digital signal on the data pin (no analog input pins needed).

Technical details:
  • Power: 3-5V
  • Max Current: 2.5mA
  • Humidity: 0-100%, 2-5% accuracy
  • Temperature: -40 to 80°C, ±0.5°C accuracy
​

What you will need - Hardware

You will also need 4x 3mm screws and glue. 

3D Printer Files

You can download the .stl 3D files from here.  

The circuit

The circuit is very simple, follow the steps below:

DHT-22:
  • Vcc to Arduino Pro mini Vcc (or 5V)
  • GNG to GND
  • ​Analog signal to Arduino pin 10

LCD Screen
  • Vcc to Arduino Pro mini Vcc (or 5V)
  • GND to Arduino Pro mini GND
  • CS to Arduino pin 4
  • RST to Arduino pin 3
  • DC to Arduino pin 5
  • DN to Arduino pin 6
  • SCLK to Arduino pin 7
  • BL to Vcc - 5V

USB cable:
Cut it and find the + and - cables. Use a voltometer or multimeter tool. Finally make the connection:
+ cable to Button switch and then to  Arduino Pro Mini Vcc pin
- cable to Arduino Pro mini GND pin

The code

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/* Arduino 3D printed Digital Thermometer
   using nokia 5110 screen and DHT-22 sensor
   Ver. 1.0 / Date:21/5/2017 */

//Include libraries
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>      //for graphics
#include <Adafruit_PCD8544.h>  //for Nokia 5110 lcd 
#include <dht.h>
dht DHT;
//Constants
#define DHT22_PIN 10     // DHT 22  (AM2302) - what pin we're connected to



//Init Display (SCLK, DIN, D/C, CS, RST)
Adafruit_PCD8544 display = Adafruit_PCD8544(7, 6, 5, 4, 3);

//Variables
int hum;  //Stores humidity value
int temp; //Stores temperature value
int maxTemp=0;
int minTemp=100;
int maxHum=00;
int minHum=100;

void setup() {

  Wire.begin();
  display.begin();
  display.setContrast(45);
  //Print a welcome message in startup for 6sec.//////////
  display.clearDisplay();   // clears the screen and buffer
  display.setTextColor(BLACK);
  display.setCursor(0,2);
  display.print("  ARDUMOTIVE  ");
  display.setCursor(0,13);
  display.print(" ArduinoBased ");
  display.setCursor(0,23);
  display.print("    Digital   ");
  display.setCursor(0,33);
  display.print("  Thermometer ");  
  display.display(); // show splashscreen
  delay(3000);
  /////////////////////////////////////////////////////////
  display.clearDisplay();   // clears the screen and buffer
}

void loop() {
  
  int chk = DHT.read22(DHT22_PIN);
  //Read data and store it to variables hum and temp
  hum = DHT.humidity;
  temp= DHT.temperature;

  if (temp>maxTemp){
    maxTemp=temp;
  }
  if (temp<minTemp){
    minTemp=temp;
  }
  if (hum>maxHum){
    if (hum==100){
      maxHum=99;
    }
    else{
      maxHum=hum; 
    }
  }
  if (hum<minHum){
    if (hum==100){
     minHum=99; 
    }
    else{
      minHum=hum;
    }
  }
  
  display.clearDisplay();   // clears the screen and buffer
  display.setCursor(0,0);
  display.setTextSize(1);
  display.println("   HUMIDITY  ");
  display.println("-------------");
  display.print("MAX ");
  display.print(maxHum);
  display.print(" MIN ");
  display.println(minHum);
  display.print("   ");
  display.setTextSize(3);
  display.print(hum);
  display.setTextSize(2);
  display.print("%");  
  display.display();
  
  delay(5000);
  display.clearDisplay();   // clears the screen and buffer
  display.setCursor(0,0);
   display.setTextSize(1);
  display.println(" TEMPERATURE ");
  display.println("-------------");
  display.print("MAX ");
  display.print(maxTemp);
  display.print(" MIN ");
  display.println(minTemp);
  display.print("  ");
  display.setTextSize(3);
  display.print(temp);
  display.setTextSize(2);
  display.print("oC");  
  display.display();
  delay(5000);
}
Download the code from here and open it with Arduino IDE. Inside you will also find all necessary libraries.
digital_thermometer_3dprinted.zip
File Size: 304 kb
File Type: zip
Download File

​Well Done!

Well...that's it!

I hope you liked this, let me know in the comments!

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