Aosong Electronics Co.,Ltd

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Your specialist in innovating humidity & temperature sensors

and temperature information to MCU. Without start signal from MCU, DHT22 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 DHT22. DHT22 will change to low-power-consumption-mode when data collecting finish if it don't receive

start signal from MCU again.

1) Check bellow picture for overall communication process:

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Host computer send out

start signal.

Data transmission finished,

Sensor send out

and RL pull up bus's voltage

response signal.

Output data: 1bit"0"

for next transmission

Pull up and wait

Host's signal

Sensor's signal

Output data: 1bit "1"

response from sensor

Sensor pull down

Pull up voltage and get

bus's voltage

ready for sensor's output.

Single-bus output

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2) Step 1: MCU send out start signal to DHT22

Data-bus's free status is high voltage level. When communication between MCU and DHT22 begin, program of

MCU will transform data-bus's voltage level from high to low level and this process must beyond at least 1ms to

ensure DHT22 could detect MCU's signal, then MCU will wait 20-40us for DHT22's response.

Check bellow picture for step 1:

Thomas Liu (Business Manager)

Email: thomasliu198518@yahoo.com.cn

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