I seem to like flooding my basement… Usually by overfilling one of my aquariums, or intentionally putting 55 gallons of water in a 45 gallon aquarium. Sometimes, I overfill the swimming pool in the back yard.
So I decided to put together a monitoring system. It will monitor my sump pump, letting me know when it is getting used hard so I know to pay it more attention. It will monitor my Aquaponics grow bed, telling me when my flood and drain / ebb & flow grow bed isn’t functioning correctly. It will also monitor my fish tank water levels and let me know when the water is getting low, or more importantly when I am filling it and it gets to where it ought to be.
This is put together with Raspberry Pis. An older original B model for the fish tank because I have it and it’s close enough to Ethernet that I can run a wire to it. The Sump Pump is getting a Zero W as it is further away, and I needed to buy something and it was the cheapest option ($10).
I am measuring water height by 2 methods. An ultrasonic distance meter and a differential pressure setup.
I coded up the project a couple of different ways, learning as I went along. I ended up starting with the hardest methods first, and moving towards easier methods. Starting at OS level triggering of shell scripts, moving through python programming, and finally landed on Node Red. I am happy for the path I took as I now have a solid understanding of what a Raspberry Pi can do for me and how to control it at multiple levels. Node Red is how I will be building most of my projects going forward as it’s easier for the kids to understand.
Node Red is a graphical programming environment that you use with a web browser. This means a quick tweak can be made from your cell phone! Not the best experience, a cell phone, but doable.
The core concept of Node Red, is you drag ‘nodes’ or blocks onto your screen and set them up with the particular details that node needs. Configuration settings such as the specific pins on the raspberry pi you have a sensor plugged into, a login for an online service, etc.
You then connect the different ‘nodes’ together with lines, and the whole thing just starts working. Amazing, really.
You program a computer using the same methods you would use to explain a process to another person. Draw a bunch of boxes saying this box does this thing, and connect the various boxes together with lines showing how different events are chained together.
When you use the Node Red menu in the Raspberry Pi, it opens up a text window, with a bunch of stuff on the screen. In amongst that text, is instructions on how to set Node Red up to turn itself on automatically when the Pi starts. Now you have automatic monitoring even if the power goes out and comes back on.
Direct reading of water level via sonar
Ultrasonic distance meters turn to out to measure the distance to a water surface fairly well. The water needs to be reasonably flat & calm for it to work reliably. The thing basically beeps at a high enough frequency that we can’t hear it, and listens to see how long until it hears it’s echo back. A little bit of math, which computers happen to be good at, and you have a distance measurement!
I picked up a bunch of HC-SR04 sensors for cheap from eBay. You can get them from reputable sources for around $5 each.
The HC-SR04 sensor tutorial I followed when writing code is found at https://www.modmypi.com/blog/hc-sr04-ultrasonic-range-sensor-on-the-raspberry-pi
If you want to learn about all of this, it is good to work through the tutorial. I ended up dropping the tutorial method and used Node Red.
Node Red needs an add-on node to ‘talk’ to the sensor. The one I found is https://flows.nodered.org/node/node-red-node-pisrf . Install it according to the instructions, restart Node Red (or the Raspberry Pi if you haven’t figured out how to restart Node Red) and reload your browser window for it, and you can now start taking distance measurements.
Differential Pressure water level method
Have you ever noticed that if you hold your finger over the end of a straw, stick it in your glass, the water goes up the straw only a little bit? When you do that, you are increasing the air pressure inside the straw.
If you compare that air pressure inside the straw, to the air pressure outside the straw, you are working with differential pressure. We can use this to simply see the cycle of water rising and falling, or calculate the actual height of the water inside the pipe. I don’t know what physics principle to use to do the math for calculating actual water height.
I used a BMP280 temperature and pressure sensor. The adafruit library didn’t work well for me. I did however find https://github.com/ControlEverythingCommunity/BMP280/blob/master/Python/BMP280.py which worked well.
The Node Red library has a bug in it at the moment. When you try to use it with the BMP280 module, it crashes Node Red. If you see this happen, the fix is simple, you need to call in the bigNumbers.js library in the right spot. Once you do this, things work correctly.
The BMP280 had some issues with longish wires. I ended up using some Cat5 with the tip from https://www.raspberrypi.org/forums/viewtopic.php?t=82049 for how to pick the wires to get the best performance. This worked well, if a bit time consuming to pigtail the doubled up wires so I only had 1 wire to solder onto the printed circuit boards.
Seeing the data
I logged the data to io.adafruit.com using MQTT. The library I used is found at https://github.com/adafruit/io-client-python for coding things the hard way. Node Red has a built in MQTT node as well.
I used Adafruit’s IO tool because it’s cheap (free) and easy, and is great for learning how to do all of this. There are other options available from Amazon, Azure, Google, IBM, and many many more. Adafruit’s tool is great to start out with.