adhesive/insulation for electronics in soil

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kevinkk525
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adhesive/insulation for electronics in soil

Post by kevinkk525 » Sat May 12, 2018 8:11 pm

I'm going to place some soil moisture sensors in my garden and I wasn't some of them to be completely covered in soil.
So I was thinking about how to insulate the electronics but was not sure which solution is the best considering that it will be quite warm and wet all the time and how the insulation/adhesive affects health.

Did someone have a similar project and made some research into this? What are you using?

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pythoncoder
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Re: adhesive/insulation for electronics in soil

Post by pythoncoder » Sun May 13, 2018 5:18 am

See this thread. He uses this sensor where the part buried in the soil is merely a PCB with two electrodes. The actual electronics are mounted remotely in a protected environment. The buried PCB requires no insulation. Although I'd solder to the pins to provide a mechanically robust connection. And use heatshrink to protect the solder joints from shorting together.
Peter Hinch

kevinkk525
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Re: adhesive/insulation for electronics in soil

Post by kevinkk525 » Sun May 13, 2018 11:12 am

Thanks, I did not see that thread.
But even he does not submerge his whole sensor and therefore does not need waterproof insulation (if he does not water the connector).
I'm using this sensors: https://www.dfrobot.com/wiki/index.php/ ... KU:SEN0193

They have quite a bit of electronics and I don't want to accidentally damage it by watering it but I also want to submerge a few into the soil, so these have to be insulated properly.

I am concerned about a shrinking plastic because of toxic ingredients that get washed out by the water and then get into my food.. (especially from chinese stuff..)
So I was wondering if anyone had a good idea or experience

chrismas9
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Re: adhesive/insulation for electronics in soil

Post by chrismas9 » Sun May 13, 2018 3:38 pm

What about silicone roof and gutter sealer? There are many brands that are approved for potable (drinking) water. You could put the electronics in a small food grade plastic container with holes in it, then completely fill it with silicone. Make sure the wires penetrate into the silicone a good distance so there is a reasonable surface area to seal. I would clean everything well with solvent ( IPA or flux cleaner, etc).

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pythoncoder
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Re: adhesive/insulation for electronics in soil

Post by pythoncoder » Mon May 14, 2018 6:06 am

kevinkk525 wrote:
Sun May 13, 2018 11:12 am
...I'm using this sensors: https://www.dfrobot.com/wiki/index.php/ ... KU:SEN0193

They have quite a bit of electronics and I don't want to accidentally damage it by watering it...
Quite. That sensor seems unusable: what happens when it rains? Unless I'm missing something that's the stupidest piece of electronic design I've seen for years. :twisted:

The whole of the top part of the sensor, complete with connector and the start of the connection lead, needs to be potted. You can buy potting compounds which solidify into a rubber like material. You'd need to enclose the top part of the sensor in some sort of box and pour in the potting compound.

Personally I'd use a resistive sensor with no electronics and do without the hassle.
Peter Hinch

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philwilkinson40
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Re: adhesive/insulation for electronics in soil

Post by philwilkinson40 » Mon May 14, 2018 6:50 am

Also check out Rienier from Vinduino. Old school, tried and tested gypsum sensors.

Everything is open source hardware and software. Not Micropython, but the sensors are simple enough.

kevinkk525
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Re: adhesive/insulation for electronics in soil

Post by kevinkk525 » Mon May 14, 2018 7:52 am

That sounds very interesting. Thank you all for your answers, I will read through it.

@pythoncoder: you are right, the sensor is not for the garden as rain would be a problem. I'm using these in my glasshouse (or balcony garden :D ) So there won't be any rain except if I make it rain by using a watering can.
But true, the design is not so good but the results are nicer than the resitive sensors and they (should) last longer. I have both sensor types and will use both.

Jim.S
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Re: adhesive/insulation for electronics in soil

Post by Jim.S » Mon May 14, 2018 7:49 pm

Caveat: the following is based on opinion rather than first hand experience:

I think you might have a conflict between your requirement to water proof your electronics and your requirement not to leach any undesirable chemicals into your soil. I believe that there are two types of silicone sealant, ones that release acetic acid as they cure and ones that do not ( I believe these are termed 'neutral') . A cursory search on the internet suggests sealants that are used for potable water release acetic acid, which *might* cause corrosion of copper wires.

My approach would be to build a housing out of plastic plumbing fittings (i.e two "stop ends" and a bit of tube) But seal the penetrations through the stop ends (i.e the sensor end and the power/signal cable) using a potting type sealant (as suggested by @Pythoncoder). Indeed, you might be able to make a waterproof but demountable case using 'push fit' type stop ends. This way you would minimise the contact of the sealant with your soil... Bus stated earlier, this is not based on first hand experience, other than a bit of plumbing....

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