Tag: IoT

Although I had this up and running back in March, it took me a while to find some time to write everything down. Here it goes.

Part 1: how does stuff work?

With my .NET application running on the Pi. I now had to see how I could monitor my water usage. Typical water meters in Belgium, or at least where I live, look quite dull but they have everything what’s needed to make them smart.

One way to get automatic readouts is to contact the supplier and let them add a logger but it’s not cheap. Their website is not really helpful but it looks like it will cost more than €100 and then there is a yearly or monthly fee. Not a valid option.

However if you do some research you’ll find info on how these meters work and chances are your meter is outputting a magnetic pulse. In the video below you will see a very nice explanation of it at around 0:35.

With my newfound knowledge I installed the application “Magnetic Detector!” on my iPhone and headed down in the basement while the tap was running and sure enough a sine wave appeared.

While doing further research I learned that detecting magnetism can be done with a reed switch or a Hall effect sensor. I chose the first one since the Hall effect sensor would need power all the time and eventually I want to replace the Pi with a tiny board. Basically the reed switch is just like a manually operated switch except it will close whenever a magnet is nearby.

Part 2: Wiring it up

I bought a reed switch for €3 and set everything up. I first tested with a regular magnet to see if everything worked and then placed my setup near my water meter.

The reed switch can be inserted into a cavity of the water meter, apparently it’s really built to accept these kinds of devices.

Part 3: Storing the readouts

With the hard part behind me, I created a free Azure web app and connected it to a free SQL database. Note that you can only create a free SQL database from within an Azure web app, if you go directly to SQL databases you will not find that option.

Since it’s a .NET app I also installed the package Newtonsoft.Json to transfer my pulse counts to the Azure web app. I spent several hours trying to get it working though as I, once again, was faced with a mysterious error.

System.TypeInitializationException: The type initializer for 'Newtonsoft.Json.JsonWriter' threw an exception. ---> System.BadImageFormatException: Could not resolve field token 0x04000493
File name: 'Newtonsoft.Json'
  at Newtonsoft.Json.JsonWriter.BuildStateArray () <0x76860c90 + 0x0009f> in <filename unknown>:0

Don’t know why, but I eventually went looking at the dependencies of Newtonsoft.Json and then explicitly updated my mono installation with the necessary bits from the Debian package list. Everything started working and uploading the pulse was just plain C#.

public void Upload(Tick tick)
{
    using (HttpClient client = new HttpClient())
    {
        client.PostAsync(_apiEndpoint, new StringContent(JsonConvert.SerializeObject(tick), Encoding.UTF8, "application/json")).Wait();
    }
}

My database started filling up and after only one day I could calculate that my showers were consuming 70 liters and the dishwasher 30 liters. Time to cut back on the time spent in the shower!

In order to keep the program running in the background I’m using a program called screen, you can find more info on that in this excellent post.

Part 4: Next steps
I had the Pi running in April, but had some issues with the Wifi. Some days I received no pulses at all and I had to reboot to gain access. Since then, well actually yesterday, I’ve changed to code to keep track of the pulse counts that failed to be uploaded and transfer them at a later time. Next up will be to create a dashboard to view the pulses or add further sensors to monitor gas and electricity.