DHT21 Temperature and Humidity Sensor

DHT21 AM2301 Capacitance Digital Temperature And Humidity Sensor Instead of SHT10 SHT11

Hygrometer Thermometer Moisture Meter Incubator Greenhouse Mushroom Terrarium Ventilation Air Conditioning Warehouse Archive Weather Station

     The DHT21 (new name AM2301) is a digital temperature and humidity sensor with cable, supplied in a black plastic case with ventilation holes. It measures relative humidity from 0% to 100% RH with typical ±3% RH accuracy and temperature from -40°C to +80°C with about ±0.5°C accuracy; it outputs both values digitally with 0.1 resolution over a single Data wire. It is powered from 3.3V - 5V and delivers a new measurement at most every 2 seconds.

     Inside the sensor are a capacitive humidity sensing element, an NTC temperature element and an 8 bit microcontroller. Each sensor is calibrated at the factory and the calibration coefficients are stored inside the sensor; therefore no user calibration or analog reading is needed and sensors are interchangeable. The difference from open board DHT22 modules is the case: the sensing element is protected against impact and dust, and the screw hole at the end of the case lets you fix it to a wall, inside a cabinet or on a box lid. Compared with the DHT11 its measuring range is also wider (the DHT11 measures only 0°C to 50°C).

     With its 59mm x 27mm x 13.5mm size and 14gr weight it is suitable for monitoring humidity and temperature in enclosed spaces such as incubators, greenhouses, mushroom rooms, terrariums, warehouses and archives. Its 3 open-ended wires (red VCC, yellow Data, black GND) connect to the control board with a terminal, connector or solder.

Key features:

     Protected case: The sensing element sits in a black ABS case with ventilation holes. Air reaches the sensor through the holes while the element is protected against touch and dust; compared with open board modules it is easier to mount inside a device or on a wall.

     Humidity and temperature in one sensor: It measures relative humidity from 0% to 100% RH and temperature from -40°C to +80°C; both values arrive in the same reading, no separate temperature sensor is needed.

     Calibrated digital output: Factory calibrated, it outputs the result digitally with 0.1 resolution over a single Data wire. No analog reading, converter or user calibration is required.

     Ready wired connection: Thanks to the 3 coloured wires leaving the case (red VCC, yellow Data, black GND) the sensor can be placed at the measuring point, away from the control board.

     Screw mounting: The mounting hole at the end of the case fixes it with a single screw; it stays in place inside an incubator, cabinet or panel.

Features:

• Product type:    Enclosed, wired capacitive digital temperature and humidity sensor
• Model: DHT21 (new name AM2301; same product)
• Humidity range: 0% - 100% RH
• Humidity accuracy: typical ±3% RH (max ±5% RH)
• Temperature range: -40°C to +80°C
• Temperature accuracy: about ±0.5°C (seller data; max ±1°C in the manufacturer datasheet)
• Resolution: 0.1 %RH / 0.1°C
• Measurement rate: one reading every 2 seconds at most
• Communication: single-bus digital output (one Data wire)
• Supply voltage: 3.3V - 5V DC (upper limit 5.2V - 5.5V in seller data)
• Calibration: factory calibrated; coefficients stored in the sensor's own memory
• Sensing elements: capacitive humidity element, NTC temperature element and 8 bit microcontroller
• Interchangeability: sensors can replace each other without calibration
• Compatible boards: Arduino, ESP32, ESP8266, Raspberry Pi, STM32 and all control boards with a digital input
• Mounting: single screw mounting hole at the end of the case
• Connection: 3 wires with open ends (solder, terminal or connector)
• Wire colours: red VCC (+), yellow Data, black GND
• Material: black ABS plastic case with ventilation holes
• Dimensions: 59mm x 27mm x 13.5mm (excluding cable)
• Weight: 14gr

Usage information:

• Connect the red wire to the 3.3V or 5V supply, the black wire to GND and the yellow wire to a digital pin of the control board. On 3.3V logic boards (ESP32, ESP8266, Raspberry Pi) power the sensor from 3.3V as well. Check the wire colours of the sensor you received before connecting.
• If no reading is obtained, add a 4.7k - 10k pull-up resistor between the yellow Data wire and VCC; on long cables this resistor makes the reading stable.
• After power-up wait at least 1 second before the first reading; read measurements at least 2 seconds apart. Reading more often does not give a new value.
• Mount the sensor with the ventilation holes open, away from heat sources (heater, lamp, motor, power supply) and direct sunlight; otherwise it measures the source rather than the environment.

Areas of use:

•  Incubator humidity and temperature control
•  Greenhouse and plant growing environment monitoring
•  Mushroom growing room humidity control
•  Terrarium and reptile care environment
•  Ventilation fan and dehumidifier control
•  Air conditioning and climate control automation
•  Warehouse, archive and cellar moisture monitoring
•  Weather station and datalogger projects
•  Smart home room temperature and humidity display
•  Humidity monitoring inside electrical panels and equipment cabinets
   

Precautions:

•  The case has ventilation holes and is not waterproof. Do not place the sensor in water, rain or where water drips on it; outdoors use it inside a rain-protected, ventilated box.
•  Do not reverse the VCC and GND wires; reverse supply can permanently damage the sensor.
•  In environments with constant condensation, chemical vapour (solvent, ammonia, chlorine) or heavy dust the humidity reading may drift; protect the sensor from these environments.
•  The sensor gives a new measurement every 2 seconds; it is not suitable for instant tracking of fast changing temperature and humidity.

Package contents:

•  1 Piece DHT21 AM2301 Enclosed Capacitive Digital Temperature and Humidity Sensor
•  1 Piece 3-core connection cable ( Assembled )
•  Note: Control board, pull-up resistor and mounting screw are not included in the package.