All of the buildings, all of those cars
were once just a dream
in somebody's head
Mercy Street - Peter Gabriel


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Pic 1

Going wireless

Since it’s a bit hard to get a dedicated wire into my house just to transfer the measurements to where I want to see them, I decided to try out a wireless solution. I ended up using the very inexpensive 433 MHz RF modules for Arduino which seems to work well for me since the signal only has to cover a distance of a few meters. On the other hand, the sender will be located below ground level and there is a metal lid above it as well that can block the signal.

But first verifying if the concept can work by making a prototype on a breadboard.

Full functioning prototype before putting them in their enclosures.

I tried it out while walking through the house and it seems that the walls don’t block the signal too much. Factors that help increasing your chances to have a successful transmission when there is no clear line of sight is choosing a low bitrate (I ended up using 300 baud) and supply the sender with a 12 Volt power supply. Using a CRC checksum as well is a good idea to make sure the measurements you receive are correct and didn’t get mangled along the way.

For the sender part I choose an Arduino Nano (small enough to fit in the enclosure). Next to the ultrasonic sensor, I also installed a temperature sensor. The idea was to compensate for the varying speed of sound as temperature changes. That part didn’t work out so well since I measure the temperature rather close to the lid while the temperature at water level can be quite different. For the transmission, an inexpensive 433 MHz RF transmitter is used. Since I wanted to give the transmitter a bit more power, I used a small 12 Volt power supply from Meanwell and a 7805 is used to derive a 5 Volt to power the Arduino.

Arduino Nano, RF transmitter and temperature sensor.

The power supply has been given its own enclosure. Mainly for space reasons. When connecting both enclosures, make sure that no water[vapor] can get inside if you want your creation to have a long and happy live.

The complete setup before installing I.
The complete setup before installing II.

After a final test, the installation can be moved to the water tank.

Installed in the rainwater tank.

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