Humdity Sensor(DHT11)
A DHT11 Sensor is a built in with a temperature sensor and moisture plates. They consist of a humidity sensing component, a NTC temperature sensor (or thermistor) and an IC on the back side of the sensor.
Working Principle:
For measuring humidity, it comprises of a built-in plate holding moisture which allow them to sense it. they use the humidity sensing component which has two electrodes with moisture holding substrate between them.
So as the humidity changes, the conductivity of the substrate changes or the resistance between these electrodes changes. This change in resistance is measured and processed by the IC which makes it ready to be read by a microcontroller.
For measuring temperature these sensors use an NTC temperature sensor or a thermistor.
A thermistor is actually a variable resistor that changes its resistance with change of the temperature.
These sensors are made by sintering of semi conductive materials such as ceramics or polymers in order to provide larger changes in the resistance with just small changes in temperature.
The term “NTC” means “Negative Temperature Coefficient”, which means that the resistance decreases with increase of the temperature.
Types of Sensors:
1.DTH11
2.DTH22
Specifications
Technical Specifications: Item Measurement Range Humidity Accuracy Temperature Accuracy Resolution 20-90%RH 0-50 ℃ ±5％RH ±2℃ 1 4 Pin Single Row
Link to datasheet:
https://components101.com/sites/default/files/component_datasheet/DHT11-Temperature-Sensor.pdf
Advantages:
Excellent, fast and response with 8-bit microcontrollers.
Disadvantages:
It has limited long term stability.
It is sensitive to dewing and certain aggressive substances.
Schematics:
Internal circuitry:
Interfacing With Arduino
Arduino Code:
#include “dht.h”
#define dht_apin A2 // Analog Pin sensor is connected to
dht DHT;
void setup()
{
Serial.begin(9600);
delay(500);//Delay to let system boot
Serial.println(“DHT11 Humidity & temperature Sensor\n\n”);
delay(1000);//Wait before accessing Sensor
}//end “setup()”
void loop()
{
//Start of Program
DHT.read11(dht_apin);
Serial.print(“Current humidity = “);
Serial.print(DHT.humidity);
Serial.print(“% “);
Serial.print(“temperature = “);
Serial.print(DHT.temperature);
Serial.println(“C “)
delay(5000);
}
Applications:
- Measure temperature and humidity
- Local Weather station
- Automatic climate control
- Environment monitoring
Referral Links:
https://www.google.co.in/search?biw=1163&bih=559&tbm=isch&sa=1&ei=-Rg9W56vKYn3vgSuiYCQCw&q=PCB+of+DTH11+sensor&oq=PCB+of+DTH11+sensor&gs_l=img.3…26116.28411.0.29061.12.8.0.0.0.0.212.761.0j4j1.5.0….0…1c.1.64.img..7.0.0….0.GDE0-WAeH5c#imgrc=5mrRI-G6To2ZfM:
http://www.circuitbasics.com/how-to-set-up-the-dht11-humidity-sensor-on-an-arduino/