HM2305 Digital-output humidity and temperature sensor

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

Description:

HM2305 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 programme in OTP memory, when the sensor is detecting, it will cite coefficient from memory.
Small size & low consumption & long transmission distance(20m) enable HM2305 to be suited in all kinds of harsh application occasions.
Single-row packaged with four pins, making the connection very convenient.

Technical Specification:

Dimensions: (unit----mm)

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
Single-bus data is used for communication between MCU and HM2305 it costs 5mS for single time communication.
Data is comprised of integral and decimal part, the following is the formula for data.
HM2305send 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, HM2305change from low-power-consumption-mode to running-mode. When MCU finishs sending the start signal, HM2305will send response signal of 40-bit data that reflect the relative humidity and temperature information to MCU. Without start signal from MCU, HM2305will not give response signal to MCU. One start signal for one time's response data that reflect the relative humidity and temperature information from HM2305 HM2305will 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:

2)Step 1: MCU send out start signal to HM2305
Data-bus's free status is high voltage level. When communication between MCU and HM2305begin, 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 HM2305could detect MCU's signal, then MCU will wait 20-40us for HM2305s response.
Check bellow picture for step 1:

3)Step 2: HM2305send response signal to MCU
When AAM2305detect the start signal, HM2305will send out low-voltage-level signal and this signal last 80s as response signal, then program of HM2305transform data-bus's voltage level from low to high level and last 80us for HM2305s preparation to send data.
Check bellow picture for step 2:

4)Step 3: HM2305send data to MCU
When HM2305is sending data to MCU, every bit's transmission begin with low-voltage-level that last 50s, the following high-voltage-level signal's length decide the bit is "1" or "0".
Check bellow picture for step 3:

If signal from HM2305 is always high-voltage-level, it means HM2305is not working properly, please check the electrical connection status.

Electrical Characteristics:

- Collecting period should be : >1.7 second.

Attentions of application:

(1) Operating and storage conditions
We don't recommend the applying RH-range beyond the range stated in this specification. The HM2305 sensor can recover after working in non-normal operating condition to calibrated status, but will accelerate sensors' aging.
(2) Attentions to chemical materials
Vapor from chemical materials may interfere HM2305s sensitive-elements and debase HM2305's sensitivity.
(3)Disposal when (1) & (2) happens
Step one: Keep the HM2305 sensor at condition of Temperature 50~60Celsius, humidity <10%RH for 2 hours;
Step two: After step one, keep the HM2305 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.
HM2305should 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 HM2305 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 HM2305may cause personal injury.

HM2305-Digital-output-humidity-and-temperature-sensor.pdf