BME280 Weather Proofing

I purchased a BME280 Humidity/Environment sensor from DFRobot BME280.

I will need to monitor humidity inside of a bin that can range anywhere between 60-95% humidity (possibly 100%). I plan on putting the microcontroller inside of a weather proof polycase Polycase Enclosure

I'll have some wire glands that run to the actual BME280 sensor. What I'm not sure of is how I should best protect the humidity sensor. I'll be growing some mushrooms so I want to try and avoid any strong chemicals, but I still need to expose the sensor.

I considered purchasing another small polycase (cheaper one that's not weather proof), enclosing the sensor inside of that, coating the entire board with clear nail polish with the exception of the actual sensor, and then drilling some small holes on the polycase.

Do you guys think that will work well given the humidity is pretty high?

For a quick and easy solution, after wiring the sensor module in, I would just pot (encase) the entire module except the sensor in epoxy.

I use the cheap weatherproof cases and then put a pneumatic muffler in the bottom to allow exchange of air but keep bugs out.

Enclosure

Muffler

It works but I don't like enclosures like this... it allows condensation and moisture to gather, in which case you may get inaccurate readings and create a situation for corrosion.

Riva: I use the cheap weatherproof cases and then put a pneumatic muffler in the bottom to allow exchange of air but keep bugs out.

Will the the muffler have a significant effect on humidity?

wolframore: For a quick and easy solution, after wiring the sensor module in, I would just pot (encase) the entire module except the sensor in epoxy.

Is there a difference between potting and covering the board (excluding the sensor) in conformal coating like this? Conformal Coating

That works. Epoxy is tougher

czu001: Will the the muffler have a significant effect on humidity?

Is there a difference between potting and covering the board (excluding the sensor) in conformal coating like this? Conformal Coating

Before you get too far with water/weather proofing an electronic device, you need to think how what lifetime you expect from the device. Will it be used only one growing season? Do you want your grandchildren to still use it? Each question relates to what type of water proofing is appropriate.

Paul

I would like it to last a few years. Do you have suggestions on how to actually encase the breakout board in epoxy with the exception of the BME sensor? Thank you so much!

czu001: I would like it to last a few years. Do you have suggestions on how to actually encase the breakout board in epoxy with the exception of the BME sensor? Thank you so much!

First, you need an enclosure shaped like a bath tub to contain both the board and the potting compound, which will be as thin as water and will run out any hole unless sealed with RTV.

Then you need to mount the circuit board so the sensor will be above the surface of the potting compound. And ensure the board will not float in the potting compound.

We buy this from Ebay: https://www.ebay.com/itm/EPOXY-RESIN-CIRCUIT-BOARD-POTTING-COMPOUND-OPAQUE-BLACK-4-CIRCUIT-MASKING-48oz-/222646149200?hash=item33d6bea050. But we get larger sizes.

Mixing instructions are with the material.

Hope this gives some help.

Paul

czu001: Will the the muffler have a significant effect on humidity?

drill a hole stuff with polyester fill from a stuffed toy. as for humidity, the mushroom farms I have been in seemed to be a constant 98% humidity. also, the BME280 is in a metal box. there is a hole on that box. you should fill the expoxy up to the lip of that box and leave the hole. that is how it breaths to sense . as a note, humidity follows the same gas laws to a very large extent. partial pressures of gasses will fill to expand the space so that the percentage is in equilibrium if the temperatures and pressures are constant and equal. temperature will be warmer higher up and colder near the floor. I expect humidity to be lower higher up and higher near the floor.

Thanks so much for the great help!!! I'll be purchasing the epoxy linked above. I think I understand now about potting the enclosure. I think I've seen "potting" boxes on polycase that are really cheap (less than $1). They also have mounting screws that can hold the board in place so that it doesn't float. Is the below link something like that?

Polycase Potting Box

dave-in-nj: also, the BME280 is in a metal box.

I didn't realize the sensor was inside of that box! Thanks so much guys for the great tips! One more question.. the DFRobot BME680 sensor I purchased has some external connectors for wires. I don't think I'll be able to easily epoxy those since I still need that sensor exposed. Will conformal coating be enough just for those? Or is there another way?

BME680

So I ended up coating the BME280 (not 680) in conformal coating instead of epoxy to start with (I did order some epoxy though).

I attached a picture of my results. I put it inside of a small polycase and drilled small holes in it. I took some readings and everything seems ok; however, when I added the polyester the readings were really high.

I’ll be putting this in an environment with 98% humidity; however, the MCU will be inside of its own polycase outside of the mushroom grow box. Do you guys think this will hold up for at least a year? Any input?

Will this be powered on all the time (and producing some waste heat)? No chance of water dripping on it? Then you have a very good chance of it lasting longer than that.

I'd try to place the sensor inside a small opening - the PCB of the sensor glued against the inside of the case. That gives the sensor full access to the outside air, without being disturbed by the inside air (which should be a bit warmer and therefore dryer than the outside air). Its temperature measurement is likely to be a bit too high due to the heat from the other components on the inside.

Then minimise the other holes to what you really need, preferably just a small ventilation hole at the bottom. The same hole that has the wires go through. That's enough to keep moisture from building up on the inside, and pressures equalised.

@CZU it has been nearly a year, do you have any updates for us? I'm trying to design a similar encasement but that protects the sensor and also keeps it away from my ESP8266 board that produces some heat. I'm thinking of a two case solution or one case that is bissected with heat a heat sink for the ESP8266 board.

Hi,
Ops pics.



Can I suggest you buy a few of the sensors and store them in a plastic bag, possibly with a bag if desiccant to keep them dry.
That way you have a ready on hand replacement for when the sensor eventually dies, and it inevitably will.

Tom... :slight_smile: