Time for a swim?

We measure & publish the temperature of out local version of municipal lake.

https://www.thethingsnetwork.org/c/munster/post/here-is-our-first-celebrity-sensor and https://www.thethingsnetwork.org/c/munster/post/weve-got-some-press-today

Pretty popular it seems.


Wow, that antenna is really close to a big metal girder! :slight_smile:

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I would like to see how this was made, and what type of battery and solar panel you are using.

Avergage power consumption is about 1,1mA when updating once every 30 minutes where 1mA is ironically consumed by the coulomb counter. This is strange as the part should have a much lower power consumption. We left it in the system as we want to learn about what happens with a little panel in a non-optimal mounting position. You can see that charge/discharge in the second graph on https://wiekaltistderkanal.de

Another little feature is that we can change the update rate via downlink command - so we can have a high rate when testing and reduce this drastically once everything is stable (to save airtime and power).

Code: https://github.com/kgbvax/kanaltemp
“Backend” and visualisation is Node Red.
Data is not only exported to the site, opensensemap,dweet but a local Elasticsearch. I plan to replace the Node Red visualisation with Kibana,

Here is what we like to improve for version 2:

  • The red case is great but also asking for trouble in the wild. People like the thing but there are always some idiots… So we’ll use something less conspicuous
  • Use steel cable ties for the same reason
  • Use two temperature sensors to get a depth profile.
  • Put the temperature sensors in a perforated plastic pipe that is only loosly affixed to the top. We hope that this makes this more robust against humans and ice as well
  • Switch the over-the-air protocol from binary to msgpack (to make it easier to change)
  • The current design has a little hole with an inward pipe attached to address condensation. I like to replace this with a membrane to make the thing really waterproof. It is currently mounted 20cm over the waterline and it gets it share of splash from ship swell. Also: the waterlevel is not as constant as we assumed.
  • Perhaps carry over an ultrasonic level sensor from another project we’re working on.
  • replace the Autonomo with something cheaper.
  • use a smaller battery
  • use cheap metal case

Let me know if you want to know specifics…


Lucky you. In my case the problem is the water level is too constant that I can’t really test my ultrasonic sensor.

Now I am interested… What do you use?

The schematics show a 3.3 kOhm pull-up resistor on the “POL” signal of the LTC4150.
Looking at the datasheet, this signal is high when the battery is charging (current flowing from out to in) but when you discharge the battery (i.e. normal use), this signal is low.

3.7V / 3.3 kOhm = 1.12 mA

The POL signal is like that little lamp telling you your battery is almost empty and now is draining even faster :disappointed_relieved:

Red box, steel ty-raps … some people just can’t keep their hands of other people’s stuff.
We has a big orange flash light (one of these old style rotating mirrors with a lamp) outdoors. Next to the door to the basement attached to the CO gas alarm. Someone just unscrewed the thing and took it home …

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@kgbvax Are you going to the TTN meetup in Enschede on Tuesday?

Yes. There is a 10% chance that work may require me to be somewhere else but I’ll try.

Fun fact: we had long and severe thunderstorms last night. Since 0:34 we haven’t recieved an update from the sensor :frowning:

The thunderstorm confused the i880 gateway board it seems. We’re back in business!

Thanks good catch.
If I can find a microscope I’ll replace the pull-ups.

Report from out local water rescue: Some imbecile stole the antenna.

The twist: It works without antenna. har har har har :smile:

(Almost: It no longer receives commands)

TODO: Use vandal proof antennas if node is accessible.

Such a shame. Put it in a floating buoy somewhere in the middle of the lake.

edit: Great URL btw :smiley:


Thanks :smile:

It’s a canal - a public waterway which extends from wall to wall at that point,so a buoy would be obstructing that waterway which will quickly be removed by the authorities.

Also, buoys may not be better off - they are used as toys by (usually adolescent) swimmers. I’d rather learn how to build things that survive in rough reality. :wink:

The rough reality is that whatever you try, there will always be someone who wants your stuff.
My gateway will be mounted outdoors on the roof of a building. It’s not a public building but there are ways to get on the roof during day-time. So I have been thinking of a few points to take care of:

  • Everything should at least be mounted “screw-tight” meaning that you need tools. Anything that looks like it can be unmounted will be …

  • Block the holes of the screws in the case or mount the case the other way around so screws are not visible.

  • Prevent the use of normal flat head or cross head, almost all pocket knifes have screwdrivers attached.

  • Make sure the equipment blends away in the environment. A bright box attracts attention, so do solar panels and antennas. In a plastic box, you could mount the antenna inside the box).

  • Steel ty-raps are a good idea. These things are mostly stainless steel, whereas the beams are completely rusted. Take some brown, rust colored paint to paint them after mounting (I use black shrink-wrap around the visible parts or the ty-raps).

  • on the other hand… steel ty-raps may make it look more like something from an official installation and that may have people rethink their actions…

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@kgbvax and me were accidently independent from each other at the location on sunday evening. Surprisingly, we found the node intact. The antenna was still there. Maybe the thief brought it back, or the nice guys from water rescue just misinterpreted something. Nevertheless, it doesn’t work again.

Use this as a casing