RHT04 Datasheet, PDF (2/5 Pages) List of Unclassifed Manufacturers – Digital relative humidity & temperature sensor

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5. Electrical connection diagram:
6. Operating specifications:
(1) Power and Pins
Power's voltage should be 3.3-6V 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
MaxDetect 1-wire bus is used for communication between MCU and RHT04. ( MaxDetect 1-wire bus is specially
designed by MaxDetect Technology Co., Ltd. , it's different from Maxim/Dallas 1-wire bus, so it's incompatible
with Dallas 1-wire bus.)
Illustration of MaxDetect 1-wire bus:
DATA=16 bits RH data+16 bits Temperature data+8 bits check-sum
Example: MCU has received 40 bits data from RHT04 as
0000 0010 1000 1100 0000 0001 0101 1111 1110 1110
16 bits RH data
16 bits T data
check sum
Here we convert 16 bits RH data from binary system to decimal system,
0000 0010 1000 1100 → 652
Binary system
Decimal system
RH=652/10=65.2%RH
Here we convert 16 bits T data from binary system to decimal system,
0000 0001 0101 1111 → 351
Binary system
Decimal system
T=351/10=35.1℃
When highest bit of temperature is 1, it means the temperature is below 0 degree Celsius.
Example: 1000 0000 0110 0101, T= minus 10.1℃
16 bits T data
Sum=0000 0010+1000 1100+0000 0001+0101 1111=1110 1110
Check-sum=the last 8 bits of Sum=1110 1110
When MCU send start signal, RHT04 change from standby-status to running-status. When MCU finishs sending
the start signal, RHT04 will send response signal of 40-bit data that reflect the relative humidity and temperature
to MCU. Without start signal from MCU, RHT04 will not give response signal to MCU. One start signal for one
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