Digital Temperature, Humidity Meter Using Arduino

In our previous article, we learned how to interface temperature humidity sensor with arduino and read out displayed on serial monitor of arduino IDE. In this post we are going to learn how to display the reading on a 16x2 LCD display for the proposed digital temperature/humidity meter using Arduino.

By: Girish Radhakrishnan

 

Introduction

This project may be used as room thermometer as well as humidity meter, since both the functionality is integrated into one sensor.

If you haven’t read the previous article yet, please check it out. It covered the basics of DHTxx series sensors.

Now, you know quite a bit about DHTxx sensors. It is better to use DHT22 sensor for projects which you are going to use for long term.

 

Author’s prototype:

The circuit:

The connection between LCD and arduino is standard, where you can find similar connection on other LCD based projects.

The program is written in such a way that, you just need to insert the DHT11 into the right port on the Arduino. This will reduce wire congestion during prototyping this project.

If you want to sense the ambient temperature around some area/circuit you may extent the wires from the sensor. So that you’re whole setup may be made inside a junk box and sensor is extended out of the junk box, like a probe.

You can use your favorite Arduino board for this project, but my suggestion is to use “Arduino pro mini” which is less expensive and small in size, which could easily fit into a small junk box for such simple projects.

There are lots of error detection mechanisms written in the DHT library to inform the user about error. But to make the program simple I have just added one error detection mechanism which is illustrated below:

Mostly errors are due to faulty connection between sensor and arduino other errors less likely to occur, since tiny amount of data is transferred between arduino and sensor. This doesn’t mean that other kind of error won’t occur.

To get an idea about all kind of error associated with this sensor, please check out example code in “DHTlib”.

Program code for the above explained digital temperature, humidity meter using Arduino :

//------------------Program developed by R.Girish-----------------//

#include <LiquidCrystal.h>

#include <dht.h>

dht DHT;

LiquidCrystal lcd(12,11,5,4,3,2);

#define DHTxxPIN A1

int p = A0;

int n = A2;

int ack;

int f;

void setup()

{

lcd.begin(16,2);

pinMode(p,OUTPUT);

pinMode(n,OUTPUT);

}

void loop()

{

digitalWrite(p,1);

digitalWrite(n,0);

ack=0;

int chk = DHT.read11(DHTxxPIN);

switch (chk)

{

case DHTLIB_ERROR_CONNECT:

ack=1;

break;

}

if(ack==0)

{

f=DHT.temperature*1.8+32;

lcd.clear();

lcd.setCursor(0,0);

lcd.print("Temp:");

lcd.print(DHT.temperature);

lcd.print("C/");

lcd.print(f);

lcd.print("F");

lcd.setCursor(0,1);

lcd.print("Humidity:");

lcd.print(DHT.humidity);

lcd.print("%");

delay(500);

}

if(ack==1)

{

lcd.clear();

lcd.setCursor(0,0);

lcd.print("NO DATA, Please");

lcd.setCursor(0,1);

lcd.print("check connection");

delay(500);

}

}

//------------------Program developed by R.Girish-----------------//

Note: The program is compatible only with DHT11 sensor

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