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Digital relative humidity & temperature sensor RHT04
1. Feature & Application:
*High precision
*Capacitive type
*Full range temperature compensated
*Relative humidity and temperature measurement
*Calibrated digital signal
*Outstanding long-term stability
*Extra components not needed
*Long transmission distance, up to 100 meters
*Low power consumption
*4 pins packaged and fully interchangeable
2. Description:
RHT04 output calibrated digital signal. It applys 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 programme in OTP memory, when the sensor is detecting, it will cite
coefficient from memory.
Small size & low consumption & long transmission distance(100m) enable RHT04 to be suited in all kinds of
harsh application occasions. Single-row packaged with four pins, making the connection very convenient.
3. Technical Specification:
Model
Power supply
Output signal
Sensing element for RH
Sensing element for T
Operating range
Accuracy
Resolution or sensitivity
Repeatability
Humidity hysteresis
Long-term Stability
Interchangeability
RHT04
3.3-6V DC
digital signal via MaxDetect 1-wire bus
Polymer humidity capacitor
Apply Dallas DS18B20 for detecting temperature
humidity 0-100%RH;
temperature -40~100Celsius
humidity +-2%RH(Max
+-5%RH); temperature +-0.3Celsius
humidity 0.1%RH;
humidity +-1%RH;
+-0.3%RH
+-0.5%RH/year
fully interchangeable
temperature 0.1Celsius
temperature +-0.2Celsius
4. Dimensions: (unit----mm)
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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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our specialist in innovating humidity & temperature sensors
response data from RHT04 that reflect the relative humidity and temperature. RHT04 will change to standby status
when data collecting finished if it don't receive start signal from MCU again.
See below figure for overall communication process,
the interval of whole process must beyond 2 seconds.
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1) Step 1: MCU send out start signal to RHT04 and RHT04 send response signal to MCU
Data-bus's free status is high voltage level. When communication between MCU and RHT04 begins, MCU will
pull low data-bus and this process must beyond at least 1~10ms to ensure RHT04 could detect MCU's signal, then
MCU will pulls up and wait 20-40us for RHT04's response.
When RHT04 detect the start signal, RHT04 will pull low the bus 80us as response signal, then RHT04 pulls up
80us for preparation to send data. See below figure:
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our specialist in innovating humidity & temperature sensors
2). Step 2: RHT04 send data to MCU
When RHT04 is sending data to MCU, every bit's transmission begin with low-voltage-level that last 50us, the
following high-voltage-level signal's length decide the bit is "1" or "0". See below figures:
Attention:
If signal from RHT04 is always high-voltage-level, it means RHT04 is not working properly, please check the
electrical connection status.
7. Electrical Characteristics:
Items
Power supply
Current supply
Collecting
period
Condition
DC
Measuring
Stand-by
Second
Min
3.3
1
40
Typical
5
Null
2
Max
6
1.5
50
Unit
V
mA
uA
Second
8. Attentions of application:
(1) Operating and storage conditions
We don't recommend the applying RH-range beyond the range stated in this specification. The RHT04 sensor
can recover after working in abnormal operating condition to calibrated status, but will accelerate sensors' aging.
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(2) Attentions to chemical materials
Vapor from chemical materials may interfere RHT04's sensitive-elements and debase RHT04's sensitivity.
(3) Disposal when (1) & (2) happens
Step one: Keep the RHT04 sensor at condition of Temperature 50~60Celsius, humidity <10%RH for 2 hours;
Step two: After step one, keep the RHT04 sensor at condition of Temperature 20~30Celsius, humidity >70%RH
for 5 hours.
(4) Attention to temperature's affection
Relative humidity strongly depend on temperature, that is why we use temperature compensation technology to
ensure accurate measurement of RH. But it's still be much better to keep the sensor at same temperature when
sensing.
RHT04 should be mounted at the place as far as possible from parts that may cause change to temperature.
(5) Attentions to light
Long time exposure to strong light and ultraviolet may debase RHT04's performance.
(6) Attentions to connection wires
The connection wires' quality will effect communication's quality and distance, high quality shielding-wire is
recommended.
(7) Other attentions
* Welding temperature should be bellow 260Celsius.
* Avoid using the sensor under dew condition.
* Don't use this product in safety or emergency stop devices or any other occasion that failure of RHT04 may
cause personal injury.
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