How to get Time Series Chart of the room Temperature, Relative Humidity and Humidity Deficit with 3$ sensor "DHT22" and Raspberry Pi without any electronic works nor any programming.

DHT22 (AM2302) CO2 Sensor

Though DHT22 (another name AM2302) sensor is small and low-cost, but have decent quality of precision of measuring temp/humidity.
You can buy the ready to use breakout of DHT22 for 3 - 4$ from eBay.

Why measure the room humidity as well as temperature

Not only to get comfortable air, to measure and control humidity has a lot of purpose, for example:

- In hight humidity room like summer or monsoon season on Japan, where I live in, It often grows the mold everywhere on the wall, clothes, food and so on. The mod can't be active under low relative humidity. I'm controlling my room to keep relative humidity under 60% to block to grows the mold.
The filamentous fungi, which is many of the causes of plant disease, is in the same family of mold, so a lot of plant disease also can avoid by humidity control. 

- Some plant is known that they close there pore under hight Humidity Deficit (I'll explain this later) to block loosing there moist and dying. With closing pore, they can't get CO2 in the air and can't grow more. So, in the veritable plant, it's popular to watch Humidity Deficit.
Humidity Deficit is strongly related to the ability of drying. A wet clothes became dry faster in the higher Humidity Deficit room

Humidity Deficit is the difference between the maximum amount of moisture the air can contain and the actual amount of moisture the air contains now. The unit is g/㎥, indicate how much gram of water can be evaporate into the 1㎥ air.


Get following Time Seriese Chart.

Cabling sensor and Raspberry Pi

The breakout board has 3 Pins, each pin head is printed as "+", "out", "-".

Connect there with RaspberryPi's GPIO as:

  • 3.3V on RPi and "+" on DHT22
  • GND(0v) on RPi and "-" on DHT22
  • wPi 29 on RPi and "out" on DHT22

Followings are example of cabling, you can free to use other 3.3v and 0v Pin on the RPi.

Connect with a M2.5 Hex Spacer.

DHT22 can fix well on the Raspberry Pi by M2.5 Spacer as follow:
In my experience, M2.6 Spacer is slightly tight, so M2.5 fit well.
You can buy M2.5 Nylon Spacer set from eBay, Metal Space set also available from eBay.

Activate a value element on the MONITOR™

MONITOR™ has one active view element for display of image data, and 3 inactive value element for display of sensor data. First of all, you should activate these value element for your temperature, relative humidity and humidity deficit data.

Go to MONITOR™, then open Elemens menu

 At first,  only one  View Element is active

Change one of your  Value Element  to Active  and Save this setting.

Then, blank Value Element will soon open.

Keep these 3 of "value_id" to post the Sensor Data to this.

Install & setting dht22 software UedaTakeyuki/dht22 on your Raspberry Pi

The Software is available here. Install & it on your Raspberry Pi by following the steps here.
Please note that you shoud use these value_id which you get at last step, as parameter of command.
After Raspberry Pi power on, dht22 software running on the Raspberrry Pi, send Temperature, Relative Humidity and Humidity Deficit data to the MONITOR™ service at 5 minute interval.
On your Web Browser, MONITOR™ keep refresh these time-series chart.


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