Building a underwater wifi sensor ?

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Not entirely related to pimatic …
I want to build a underwater temperature sensor with a ESP sending it to pimatic. There are a few problems on the road to be taken:

• Waterproof IP68
• How far can wifi reach underwater ?
• Battery lifetime

First things first, I need to test with a simple enclosure if wifi would work underwater. For my specific situation rang isn’ta issue. I have a AP hanging a few meters from the site I want to go underwater.
If wifi seems to work underwater it is time to find a cheap housing. Looking at ebay I think the cheapest way to go is using a GoPro or phone case with IP68 rating.
Next step : battery life. I think we can get a long runtime when only measring every 10 minutes and goto deep sleep after sending. It’s no problem that the ESP goes to very deep sleep without being able to contact or do stuff.

Any ideas? Does anyone has experience with such a project ? I won’t take no for an answer, if wifi isn’t possible I want to find it out myself

@koffienl This won’t work unless you manage to place the antenna above the water surface.

“Water’s resonant frequency is in the 2.4GHz band, which is why microwave ovens use it (and why there’s an open band there). This means that water will absorb 2.4GHz waves extremely well. So, it will work underwater, just not very far. A few feet at most. My GoPro can be controlled via wifi, and when I dunk it under the surface of the water, it loses connection.”

https://www.quora.com/Does-Wi-Fi-work-underwater

I’m extemely stubborn on such cases I wan’t to try and find out myself it it works or not
My disctance isn’t very long and if needed I could try building a external antenna. I only need to go about 40 cm in the water.

@koffienl said:

I’m extemely stubborn on such cases

Ok, give it a try and please let us know about your findings

As the guy said it will work for a few feet perhaps (may be 10 cm distance to give a bet), but he already lost connection by just getting the go-pro right under the water surface.

I hop to do some tests tommorow and will report back

It will not work with the antenna in water.
As @mwittig has describe, the Water resonates with 2,4GHz.

Of course i am interesting in your results.

40cm? why the hell don´t you put your esp over water… and put only the sensor under water?
that´s what im doing here since 2 years or so…

there are waterproof versions of ds18b20… but you can make your own waterproof ones… just put the sensor with cable into a hose… heat up the end… untill it is squashy… then press it with some sort of pliers…
finished…

example:

@demlak is right. why not use a waterproof ds18b20 with longer cable and put the esp over water. on ebay they are sold for few euro only http://m.ebay.de/itm/Temperaturfuehler-DS18B20-Thermosensor-Temperatur-Sensor-Wasserdicht-Kabel-YJ-/262204004666?nav=SEARCH

or tinker yourself something similar.

I’m aware of the waterproof DS18B20 sensors, but I want a more permament and nice looking solution for my pool. Hanging a hose with a sensor in it is not a permanent and nice looking thing

I allready have 2 sensors in my plumbing, but the values only are meaningfull when the pump is running, otherwise i’m measuring still water in the plumbing.

well then you might check it out with an underwater case. am curious about your findings !

Again, I don’t think it will work unless the antenna is above the water level.
How about this: Use a rubber duck and mount a small antenna on top (basically, a piece of wire). The antenna’s pig tial can be put through the duck’s interior to small hole at the bottom. As the sensor box with the pcb and antenna may be quite heavy and may cause the duck sinking if it just hanging below under the water, I think it would be better to attach the box at a pool wall. Instead of using a regular pigtail cable which will be rather expensive you can also use a shielded cable (it should be rated for high frequency application).

Hmm that’s a good idea
I have had some RF poolthermometers floating on the water surface, but couldn’t get the RF to work in pimatic, and I want to get rid of RF. A other good looking China floater works very well but multiple editions were lost because they keep leaking. That’s why I want to build my own. But it’s a goed idea to build something floating myself.

@koffienl How about this artificial water lily which even can carry a small PCB - http://www.thingiverse.com/thing:921163

Interesting! We have a 3D Printer @ work. My only concern is getting the stuff waterproof, normal filament is nog waterproof. Curious it the instructions on the page are enough to prevent getting water in the thing.

Printing

Update : the water lely is ginving print problems, not coming out as expeced. Next step is to try to print a chlorine floater with a compartment in the bottom that will fill itself with water. Above this compartment (bu under water level) the water can be placed.

I have not read all, but why didn’t you use this sensor?
http://m.aliexpress.com/item/1297739612.html?productId=1297739612&productSubject=&aff_platform=aaf&sk=AYNZJMJiE%3A&cpt=1454482684913&aff_trace_key=01725493f85f47e0ba5d27608c2b6f25-1454482684913-09303-AYNZJMJiE&tracelog=wwwdetail2mobilesitedetail
It costs around 1$ and is waterproof.

@Icesory said:

I have not read all, but why didn’t you use this sensor?
http://m.aliexpress.com/item/1297739612.html?productId=1297739612&productSubject=&aff_platform=aaf&sk=AYNZJMJiE%3A&cpt=1454482684913&aff_trace_key=01725493f85f47e0ba5d27608c2b6f25-1454482684913-09303-AYNZJMJiE&tracelog=wwwdetail2mobilesitedetail
It costs around 1$ and is waterproof.

was already mentioned

@Icesory said:

I have not read all, but why didn’t you use this sensor?
http://m.aliexpress.com/item/1297739612.html?productId=1297739612&productSubject=&aff_platform=aaf&sk=AYNZJMJiE%3A&cpt=1454482684913&aff_trace_key=01725493f85f47e0ba5d27608c2b6f25-1454482684913-09303-AYNZJMJiE&tracelog=wwwdetail2mobilesitedetail
It costs around 1$ and is waterproof.

Because it doens;t look nice to have a wire from the shed to a pool in a PVC tube

The chlorine floater isn’t going to work either, to much print problems. Currently me and my colleagues are designing our own floater. It is based on a chloring floater.
The lowest part of the ‘tube’ is going to be made to fill with water. This is for floating stability and will also be the part where the outerpart of the sensor is going to be. Above this compartment will be a hollow tube where the water can’t come. There will be the ESP, wiring and battery.

When this works I want to go a step further and add a small solar panel, charger and LiPo battery. That, with deep sleep, should make it allmost self–sustaining. If it needs 1 or maybe 2 charges a year than thats fine for me.

@koffienl said:

Because it doens;t look nice to have a wire from the shed to a pool in a PVC tube

I didn’t know you were a lady caring about these “external frivolities”