The humidity sensor is also called a hygrometer that senses, measures and gives us reports about both moisture and temperature of the air. Humidity sensor work by detecting changes that alter electrical currents or temperature within the air surrounded by us. The ratio of moisture in the air to the highest amount of moisture at a particular air temperature is called relative humidity. Relative humidity becomes an important factor when looking for comfort.
There are three basic types of humidity sensors:
Capacitive Resistive Thermal
A capacitive humidity sensor measures relative humidity with the help of a thin strip of metal oxide between two electrodes. The metal oxide’s electrical capacity changes with the atmosphere’s relative humidity. The major application areas are Weather, commercial and industries. The capacitive type sensors are linear type and can measure relative humidity from 0% to 100%.
Resistive humidity sensors utilize ions in salts to measure the electrical impedance of the atoms. As humidity changes, the resistance of the electrodes on either side of the salt medium changes.
Two thermal sensors conduct electricity based upon the humidity present in the surrounding air. One sensor is enclosed in dry nitrogen while the other measures ambient air. The difference between the two sensors measures the humidity.
Each humidity sensor mentioned above has its own pros and cons. In this, we are using DHT11 which is a capacitive humidity sensor.
The DHT11 is available at low-cost, It is very convenient to use and consists of the capacitive humidity sensor and a thermistor to measure the surrounding air and gives out a digital signal on the data pins(no analog input pins is needed).
Humidity measurement in industries is critical because it may affect the business cost of the product and the health and safety of the personnel. So, its huge importance of humidity sensor, especially in the control systems for industrial processes like chemical gas purification, dryers, ovens, film desiccation, paper and textile production, and food processing. In agriculture, measurement of humidity is important for plantation protection (greenhouse), soil moisture monitoring, etc.
WORKING OF DHT11
As I told you before, it consists of a humidity sensing component, an NTC temperature sensor (or thermistor) and an IC on the backside of the sensor.
The humidity sensing component has two electrodes containing moisture holding substrate between them. When the humidity changes, the conductivity of the substrate changes so the resistance between these two electrodes changes. This change in resistance is measured and processed by the IC thus humidity is measured.
We use the NTC temperature sensor (thermistor) to measure the temperature of the air.NTC means negative-temperature-coefficient. As the temperature increases, the resistance decreases or vice-versa.
SPECIFICATIONS OF DHT11
Pin
Description
VCC
3.3/5V DC SUPPLY (INPUT)
GND
GROUND( INPUT)
DOUT
DATA PIN (OUTPUT)
NC
NO CONNECTION PIN
Operating Voltage : 3.5V to 5.5V Operating current : 0.3mA (measuring) 60uA (standby) Output : Serial data Temperature Range : 0°C to 50°C Humidity Range : 20% to 90% Resolution : Temperature and Humidity both are 16-bit Accuracy : ±1°C and ±1%
The connection of Arduino-Uno with humidity sensor(DHT 11) is done as follows:
Connect the ground of Arduino-Uno with the ground of the DHT-11 sensor(It is indicated by black wire in the fig.3.)
Connect the 5v pin of Arduino-Uno to the VCC of DHT-11(It is indicated by red wire in the fig.3.)
Connect any one of the digital pins of Arduino-Uno with the data pin(DOUT) of DHT-11 to read values from the humidity sensor. (It is indicated by blue wire in the fig.3.)
SOURCE CODE FOR INTERFACING ARDUINO-UNO WITH DHT-11
// Code for DHT-11 humidity and temperature sensor
#include
#define dataPin 2 // Defines pin number to which the sensor is connected
dht DHT; // Creates a DHT object
void setup()
{
Serial.begin(9600);
}
void loop()
{
int readData = DHT.read11(dataPin); // Reads the data from the sensor
float t = DHT.temperature; // Gets the values of the temperature
float h = DHT.humidity; // Gets the values of the humidity
// Printing the results on the serial monitor
Serial.print("Temperature = ");
Serial.print(t);
Serial.print(" *C ");
Serial.print(" Humidity = ");
Serial.print(h);
Serial.println(" % ");
delay(1000); // Delays 1 seconds, as the DHT11 sampling rate is 1Hz.
}
Once we upload this code into the Arduino board, the temperature and humidity values are read from the sensor and we can see it on the serial monitor.
CONCLUSION
The above-discussed information is all about interfacing Arduino with the DHT-11 sensor to monitor the humidity and temperature of the air. The basic information about the humidity sensors is also discussed.
