DHT11- Temperature sensors basics

1. Temperature and Humidity
Sensor(DHT11)

2.  DHT11 is a digital sensor for sensing temperature and
humidity.
 To measure the surrounding air this sensor uses a
thermistor and a capacitive humidity sensor.
Introduction

3.  It has two main part one is used for temperature
measurement and other is used for humidity
measurement
Principle

4.  It consists of NTC sensor or thermistor to measure the
temperature
 Thermistor is basically a variable resistor which changes its
resistance with change in temperature
 These thermistors made by sintering semiconductor
materials such as ceramic or polymers in order to large
change in resistor with small change in temperature.
 When temperature changes there is a change in resistance
of the thermistor by this we can find the temperature of
our environment
DHT11 Temperature measurement
part

5. DHT11 Temperature measurement

6.  For Humidity measurement it uses humidity
component which has two electrodes with humidity
holding substrate between them
 As moisture content changes in our environment the
conductivity changes or resistance between electrode
changes.
DHT11 Humidity measurement

7. DHT11 Humidity measurement

8. Circuit Diagram

9.  DHT11 sensor consists of capacitive humidity sensing
element and a thermistor for sensing temperature.
 The humidity sensing capacitor has two electrodes
with the moisture holding substrate as dielectric
between them
 Change in the capacitive value occusrs with the
change in humidity levels.
 The IC measure process this changed resistance
values and change them into digital form
Explanation

10.  For measuring temperature this sensor uses a
negative temperature coefficient thermistor
 Which causes a decrease in its resistance value as
increase in temperature.
 To get the larger resistance value even for the
smallest change in temperature
 This sensor is made up of semiconductor ceramics
and polymers
Explanation

11.  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%
Features

12.  Excellent quality
 Fast response
 Anti-interference ability
 Extremely accurate calibration of humidity calibration
chamber
Advantages

13.  Since DHT11 uses capacitive humidity sensing method
it has limited long term stability
 It is sensitive to dewing and certain aggressive
substances
Disadvantages

14.  It is used in ventilation and air conditioning systems
 Predict the weather conditions
 Humidity sensors is used in a preventive measure in
homes
 Offices, cars, museums industries
Applications