Using BME280 Temp Sensor Outdoors

I'm building a Raspberry Pi based weather station just for shits and giggles and wanted to know how I could "weatherproof" the Bosch BME280 temp & humidity sensor?

This is what the sensor looks like:



Exposing it directly to the outdoors will probably damage it - is there a way to protect the sensor from the elements whilst also making sure it's measuring the outside temp, not the temp inside a box?

 

It it were only temp, you could solder a copper wire to the case and run it out of the box through a cable gland. The dip the board in epoxy to seal it.
However the humidity sensor will cause you problem. Seal it a box, and the reading won't be very meaningful (it'll tell you when the box starts to leak).

2.

 

Yeah, dipping it in epoxy or keeping it in a box won't give accurate readings

Was thinking about getting a piece of pipe with a cap putting the sensor inside and keeping the bottom exposed - don't know how that would impact the temp readings, but should be fine for humidity.

 

Flipped through the datasheet and...

More or less the device will work in a general purpose, vented enclosure in most circumstances. The key factor of allowing all the functions to work is exposure of the little hole in the cap to the environmental air that you're interested in.

If I were to protect the module more, I might cover the chip, coat/epoxy the board (with a plug well to ensure the top cap remains exposed), remove the plug to expose the chip and then insert it into a ventilated box, depending on the conditions filtered or rain protected.

If you need to reject sprayed water or submersion, you may need to investigate the use of gore-tex or another type of hydrophobic film.

 

Hmm, covering it all in an epoxy and leaving the actual sensor free is relatively easy. Wonder what would happen if rain got in to the sensor's vent? Would read as 100% humidity, even though it may not be that humid outside?

 

Probably. More concerning is that unlike condensation, rainwater is relatively impure, and it's those impurities that will probably do the long term damage.

It's rated to permitting 100% RH in operation and condensation when unpowered, so it's probably resistant to just being wetted by relatively pure water.

 

I'd cover the top of the sensor with masking tape and dip/spray the rest with conformal coating.

 

Quick search for easy looking enclosures to make yielded this:

https://store.vaisala.com/au/productresources/large1/HMS82.jpg

Should be easy enough to make out of stuff you can get at Bunnings and will protect the device from everything except rain that's raining upwards lol.

 

Good thinking - I found this page for schools wanting to make their own weather stations: http://www.weatherforschools.me.uk/html/settingup.html

Has instructions on how to make one of those enclosures on the cheap. I'll make one, chuck the BME280 board in it and that should keep it safe I reckon.

 

I installed a fairly fancy Davis weather station and it used what looked like a stack of half a dozen or so inverted disposable plastic plates spaced about 1-2 cm apart with the sensor somewhere in the middle - it wouldn't be hard to roll your own.

 

Yep - that's what I'll roll out I reckon

 

Yeah I've built similar before, there is lots of DIY info available in the internet for radiation shields, or even fan assisted radiation shields (FARS).

You need them not just for the weatherproofing but also to stop the sun giving you false readings. The temp sensor is affected by the radiant heat, and humidity sensors I have used before are also affected by strong light.

 

Pretty ghetto, but put it in an opaque box so the bottom side of the box is open, then a 5w solar panel and a case fan to keep the air temp in the box the same as outside.

Like the FARS above but way shonkier.

James

 

Buy/build a Stevenson screen. They tend to be a bit more accurate than a standard radiation shield, however I'm not too sure about protecting from the elements. You could try a small sealed plastic enclosure with holes drilled in it. I would use a piece of fine mesh glued on the inside to prevent bugs getting in and making it easier to clean. I would also look at some way of waterproofing the connector so bugs don't get in that way, because bugs are just as big of a concern as the environment.

I don't think the temp sensor or barometer really needs to be fully exposed, because air temperature and pressure doesn't change that quickly. You also have barometers inside phones, watches, etc.

If you were really pedantic like me, you could try some conformal coating on every IC except the barometer and humidity sensor. I'm not sure if this affects the readings of the temp sensor so keep this in mind.

Really I think the biggest thing is figuring out how to make your enclosures in such a way that they don't influence temperature readings, which is why a stevenson screen is important. If you're going to make your own radiation shield, I wouldn't bother with the plate-style radiation shield, just use a stevenson screen.

Hope this rambling kinda helps a bit.

 

Cheers trackhappy! Helpful info