DHT 21

Feature & Application:

– Full range temperature compensated

– Relative humidity and temperature measurement

– Calibrated digital signal

– Outstanding long-term stability

– Extra components not needed

– Long transmission distance

– Low power consumption

– 4 pins packaged and fully interchangeable



DHT 21

The DHT 21 output calibrated digital signal. It utilizes exclusive digital-signal-collecting-technique and humidity sensing technology, assuring its reliability and stability.Its sensing elements is connected with 8-bit single-chip computer. Every sensor of this model is temperature compensated and calibrated in accurate calibration chamber and the calibration-coefficient is saved in type of program in OTP memory, when the sensor is detecting, it will cite coefficient from memory. Small size & low consumption & long transmission distance(20 m) enable DHT 21 to be suited in all kinds of harsh application occasions. Single-row packaged with four pins, making the connection very convenient.

DHT 21

(1) Power and Pins

Power’s voltage should be 3.3-5V DC. When power is supplied to sensor, don’t send any instruction to the sensor within one second to pass unstable status. One capacitor valued 100nF can be added between VDD and GND for wave filtering.

(2)Communication and signal

Single-bus data is used for communication between MCU and HM2301, it costs 5ms for single one time communication. Data is comprised of integral and decimal part, the following is the formula for data. HM 2301 send out higher data bit firstly! DATA=8 bit integral RH data+8 bit decimal RH data+8 bit integral T data+8 bit decimal T data+8 bit check-sum If the data transmission is right, check-sum should be the last 8 bit of “8 bit integral RH data+8 bit decimal RH data+8 bit integral T data+8 bit decimal T data”. When MCU send start signal, HM 2301 change from low-power-consumption-mode to running-mode. When MCU finishs sending the start signal, HM2301 will send response signal of 40-bit data that reflect the relative humidity and temperature information to MCU. Without start signal from MCU, DHT21 will not give response signal to MCU. One start signal for one time’s response data that reflect the relative humidity and temperature information from HM2301. HM2301 will change to low-power-consumption-mode when data collecting finish if it don’t receive start signal from MCU again.By liking Our Facebook Page Embeded Studio , you can get special discount


  • DHT21 is the former name, new name is AM2301
  • 4-pin package
  • Ultra-low power
  • No additional components
  • Excellent long-term stability
  • All calibration, digital output
  • Completely interchangeable
  • Long distance signal transmission
  • Relative humidity and temperature measurement
  • Specifications:
    • Type: AM2301
    • Accuracy resolution: 0.1
    • Measurement range: 0-100%RH
    • Temperature measurement range: -40℃ ~ +80℃
    • Humidity measurement precision: ±3%RH
    • Temperature measurement precision: ±0.5℃
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