DHT11 Sensor

The DHT11 is a basic, ultra low-cost digital temperature and humidity sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and spits out a digital signal on the data pin (no analog input pins needed).

994 Views, 03 Nov 2017 12:35 pm

Description

The DHT11 is a basic, ultra low-cost digital temperature and humidity sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and spits out a digital signal on the data pin (no analog input pins needed).
For measuring humidity 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.
On the other hand, for measuring temperature these sensors use a 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.
The data from the DHT11 sensor consists of 40 – bits and the format is as follows:
8 – Bit data for integral RH value, 8 – Bit data for decimal RH value, 8 – Bit data for integral Temperature value, 8 – Bit data for integral Temperature value and 8 – Bit data for checksum.
These 40 bits can be converted to decimal values by using checksum methods.
By using dht.h library we can directly get the temperature and humidity values in decimal format.
Specifications:
• Low cost • 3 to 5V power and I/O • 2.5mA max current use during conversion (while requesting data) • Good for 20-80% humidity readings with 5% accuracy • Good for 0-50°C temperature readings ±2°C accuracy • No more than 1 Hz sampling rate (once every second) Pins: • VCC-3.3v • OUT-digital pin of Arduino • GND-ground

Some DHT11 sensors may have four pins then the pins should be connected as follows: • VCC-3.3v • OUT-digital pin of Arduino • NC- No connection pin (simply leave that pin) • GND-ground Applications: • Can be used to monitor the temperature and humidity parameters and design the systems like smart weather monitoring and smart environment monitoring system.