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DHT11 sensor example

In this example we will show a basic example of connecting a DHT11 Temperature and Humidity Sensor to your Arduino. This is a very nice little, low cost sensor which requires only a pull up resistor to VDD. This can easily be constructed on a mini bread board and then joined up to your Arduino. using some connecting cables

The DHT sensors are made of two parts, a capacitive humidity sensor and a thermistor. There is a chip inside that does some a/d conversion and outputs a digital signal with the temperature and humidity.

I wont go into the technical details of the DHT11, there is a link at the bottom to a PDF datasheet which explains all you need to know.

Schematic

Arduino and DHT11 schematic

Arduino and DHT11 schematic

Connections

Here is the breadboard layout

Arduino and DHT11 breadboard

Arduino and DHT11 breadboard

Code

You will need the DHT11 library from the DHT library. You could roll your own code but this saves a whole lot of time.

Download, extract and copy this to your Arduino libraries folder location. This is a simple example which outputs the humidity and temperature, place your fingers on the DHT11 and you will see the readings fluctuate

#include <dht11.h>

dht11 DHT;
//Pin 4 of Arduino to Data of DHT11
#define DHT11_PIN 4

void setup()
{
Serial.begin(9600);
int check;
Serial.print(“DHT11 STATUS – \t”);
check = DHT.read(DHT11_PIN);
//check status
switch (check)
{
case DHTLIB_OK:
Serial.print(“OK\n”);
break;
case DHTLIB_ERROR_CHECKSUM:
Serial.print(“Checksum error\n”);
break;
case DHTLIB_ERROR_TIMEOUT:
Serial.print(“Timeout error\n”);
break;
default:
Serial.print(“Unknown error\n”);
break;
}
}

void loop()
{

//humidity and temperature output
Serial.print(“Humidity is “);
Serial.print(DHT.humidity,1);
Serial.print(“\n”);
Serial.println(“Temperature is “);
Serial.println(DHT.temperature,1);

delay(1000);
}

Output

Upload the sketch above and open the Serial Monitor window

arduino and dht11 serial output

arduino and dht11 serial output

 

Parts List

Label	Part Type
DHT1	DHT11 Humitidy and Temperature Sensor	
Part1	Arduino Uno (Rev3)
R1	4.7k Ω

 

Links

DHT11 Humidity and Temperature Sensor from Amazon UK

DHT11 Humidity and Temperature Sensor from Amazon US

DHT11 Datasheet in PDF format

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DS18B20 temperature sensor

The DS18B20 is a  temperature sensor that can be used in various simple projects.  This part uses the 1 wire (I2C) bus and you can connect multiple sensors up to your Arduino.

The part is also relatively low cost and only requires an additional 4k7 pull up resistor. In the example below we shall make a basic example that reads the temperature and outputs via serial and can be verified using the serial monitor in the Arduino IDE.

Lets look at the parts list

Parts List

Label Part Type
DS1 DS18B20 1-Wire Temperature Sensor
Part1 Arduino Uno (Rev3)
R1 4.7k Ω Resistor

Layout

As always be careful not to get the connections incorrect, you can refer to the pinout for the device below to help . The DS18B20 can be powered by between 3.0V and 5.5V so you can simply connect its GND pin to 0V and the VDD pin to +5V from the Arduino Duo.

ds18b20 pinout

ds18b20 pinout

 

Here is the connection diagram showing how to connect your arduino to the resistor and sensor.

ds1820 breadboard

ds1820 breadboard

Coding

You need to download 2 libraries and copy them into your Arduino libraries folder.

Dallas 18b20 Temperature Library
“1-Wire” Library

Now copy and paste this into a new sketch

#include <OneWire.h>
#include <DallasTemperature.h>

//the pin you connect the ds18b20 to
#define DS18B20 2

OneWire ourWire(DS18B20);
DallasTemperature sensors(&ourWire);

void setup()
{
Serial.begin(9600);
delay(1000);
//start reading
sensors.begin();
}

void loop()
{
//read temperature and output via serial
sensors.requestTemperatures();
Serial.print(sensors.getTempCByIndex(0));
Serial.println(” degrees C”);
}

When you upload the sketch, go to Tools -> Serial Monitor and you should see something like the following. Put your finger  on the DS18B20 and you should see the temperature vary.

 

ds18b20 output

ds18b20 output

Links

DS18B20 links

Buy DS18B20 from Amazon UK

Buy DS18B20 from Amazon US

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