Temperature and Humidity Sensor

 Introduction to Temperature & Humidity Sensor

These sensors are very fashionable for electronics hobbyists because there are rock bottom but still providing great performance. Here are the most specifications and differences between these two sensors:

The DHT22 is that the costlier version which obviously has better specifications. Its temperature measuring range is from -40 to +125 degrees Celsius with +-0.5 degrees accuracy, while the DHT11 temperature range is from 0 to 50 degrees Celsius with +-2 degrees accuracy. Also, the DHT22 sensor features a better humidity measuring range, from 0 to 100% with 2-5% accuracy, while the DHT11 humidity range is from 20 to 80% with 5% accuracy.

There are two specifications where the DHT11 is best than the DHT22. That’s the rate which for the DHT11 is 1Hz or one reading every second, while the DHT22 rate is 0,5Hz or one reading every two seconds and also the DHT11 features a smaller body size. The operating voltage of both sensors is from 3 to five volts, while the max current used when measuring is 2.5mA.

How does it Work?

 These sensors actually work. They contain a humidity sensing component, an NTC temperature sensor (or thermistor) and an IC on the backside of the sensor.

For measuring humidity they use the humidity sensing component which has two electrodes with moisture holding substrate between them. So because of the humidity changes, the conductivity of the substrate changes or the resistance between these electrodes changes. this alteration in resistance is measured and processed by the IC which makes it able to be read by a microcontroller.

On the opposite hand, for measuring temperature these sensors use an NTC temperature sensor or a thermistor.

A thermistor is really a rheostat that changes its resistance with the change of the temperature. These sensors are made by sintering of semiconductive materials like ceramics or polymers so as to supply larger changes within the resistance with just small changes in temperature. The term “NTC” means “Negative Temperature Coefficient”, which suggests that the resistance decreases with the rise of the temperature.

Specifications Of DHT11 Vs DHT22

There two types

2. DHT22

a. Range: 20 – 100%

b. Absolute accuracy:±2%

c. Repeatability:±1%

d. Stability: 0.5% per year

e. Operating Voltage: 3.5V to 5.5V

f. Operating current: 0.3mA (measuring) 60uA (standby)

g. Output: Serial data

h. Resolution: Temperature and Humidity both are 16-bit

Pinout of Temperature

Feature:

1. Full range temperature compensated.
   
2. Relative humidity and temperature measurement.
   
3. Calibrated digital signal.
   
4. Outstanding long-term stability.
   
5. Extra components not needed.
6. Long transmission distance.
   
7. Low power consumption.
   
8. 4 pins packaged and fully interchangeable.

Applications:

1. Measure temperature and humidity.
   
2. Local Weather station.
3. Automatic climate control.
4. Environment monitoring.