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3D Printed Radiation Shield for Meteo Stations - Part 4

Installing the Temperature / Humidity sensor

Prior we go to the physical installation of the Temperature / Moisture sensor, let's talk a little about the sensor itself.
The most common type of T/H sensors used on DIY weather stations, no mater its brand or type, use the I²C protocol to communicate over our well know SDA / SCL lines.
The I²C (Inter-Integrated Circuit) protocol, as its name seems to indicate, was developed to interconnect devices at short distances. Often, when we want to install an outdoor T/H sensor, the distance between the best location for getting accurate readings and the microcontroller used to read the sensor, exceeds the tolerances of the I²C protocol, and we have difficulties to read our sensor, or even no readings at all. Depending on the cable used and the number of devices already existent on the I²C bus, the maximum cable length we can use to connect our T/H sensor rarely can be higher than 1 meter, which is quite limiting.
How can we surpass this limitation? There are any solutions? Yes, there are. The use of the called I²C bus extenders.

Basically an extended I²C bus is composed by two small devices, one installed near the microcontroller, the other at the end of the cable where we intend to connect our sensor. By using an I²C bus extender circuit, we can have cable lengths of 50 meters or even more.
Picture bellow illustrate the concept.
 

 

There are on the market (ex eBay) many ready made modules which allow an easy implementation of an extended I²C bus.
WeatherDuino users are a little more lucky, as all of our transmitters, already include onboard the first part of an extended I²C bus, so users only need the second part of the circuit to place at the end of the cable, near the T/H sensor.
Here is a picture from our I²C bus extender PCB, which currently we offering with any of the WeatherDuino bundles.
(Real size is much smaller, only 30mm x 14mm)



The reason of this preamble before starting with the physical installation of the T/H sensor on the RS, is because depending on whether you decide to use an I²C circuit or not, you will need to add the optional small box under the RS, or not.


So, lets start with the assembling of the T/H sensor.
Case you have decided by installing a fan on the RS, then you will need to add to the sensor mounting piece a small connector for connecting the power for the fan.
Pictures bellow shows the placement of the fan connector and how I have fixed the sensor to the sensor mounting piece.
Each one can find other ways, important is that the body of the sensor stay above the mounting piece.

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If you haven't installed a fan, then, now you only need to carefully fit the sensor protection chamber into the sensor mounting piece, and insert the set inside the RS, fixing it using an M3 screw.

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If you have installed a fan, then start by partially insert the sensor protection chamber piece into the RS (see picture above on the right), then pass the fan power cable through the square hole near the top that piece. Plug the fan power cable into the connector. After that, carefully fit the sensor protection chamber into the sensor mounting piece, it should enter with some resistance. Now, just insert the sensor mounting piece inside the RS, and fix it using a small M3 screw (there is an hole on the base piece for that). The job is done!


Optionally, you may want to put inside of the sensor protection chamber some kind of dust filtration material. I did it.
Despite what may seem on the picture, the material used is fully waterproof while air can flow easily.




Continue on next topic...

Werk do you know what exactly the material is that you used for dust filtration? I have been having problems with dust killing my temperature sensor in my fan aspirated radiation shield and would like to build a similar protection chamber.