In my last blog post I have given a short insight in my worm farm and showed the idea I have using a vibration sensor, the Fast Furrier Transform (FFT) to detect leaks in the pipe system. Todays post is not about what I have planned. But see by yourself.
In this blog post:
What happened
Wow, what a week. I was eagerly waiting to know whether I would receive a vibration kit or not. While waiting I did not want to let time pass doing nothing. So, I did a lot of reading on vibration sensors and water pipes, experimented with a piezo sensor using my Arduino and learnt more on the FFT. The more days passed without having the magic message from Element 14 in my inbox, the more I knew I would not have been selected. And I was right. Thanks for DAB to give me some advice how I could improve my applications for the next time.
So what to do?
I had like several possibilities how to proceed
- give up and put the idea in the drawer
- just buy the equipment
- do it another way
The worm watering system had already cost quite a bit of money and I did not want to spend more, specially not the almost 200 Swiss francs the sensor would cost me. So, I could just give it up or do it another way.
I have chosen to do it but go my way. That mean’s not being eligible to win the computer, but I do not care too much. The farm has this possible issue with leakages and the topic is really fascinating combining physics, maths, digital signal processing and programming.
Why another Nucleo
Before this vibration competition I had never heard of Nucleo boards. And I had no idea how to program them. Thanks to Shawn Hymel there is a great series of Nucleo board tutorials on youtube.
The more videos I watched the more I realized how powerful these boards are for signal processing. I stumbled over a document on the Arm Cortex Microcontroller Software Interface Standard (shortly CMSIS). This is a library providing a consistent and simple software interface to perform a whole lot of mathematical functions like
- Basic vector operations
- Functions like sine and cosine
- Matrix computing functions
- Transform functions like the FFT
Wait, what was that. I hit the jackpot. That thing has a built-in FFT functionality. The associated firmware runs on the STM32F429xx and the STMF746xx MCUs. So I decided to order by myself the Nucleo STM32F746STM32F746.
Charge amplifier
In the past days I also did try to get as much knowledge on vibrations in pipe systems containing fluids. Luckily, I found different research teams doing exactly this mainly to detect leaks in water pipes below ground. In one of these research papers they mentioned the company called Brüel & Kjaer from Denmark. I contacted them for more information on their vibration sensors and what they would cost.
Well, for the price of one Brüel & Kjaer sensor I would be able to buy several vibration sensors from Kemet. The good thing was, that they not only send me the price list, but added some advice on my project.
Sensing the vibrations of the pipe would not be possible with their sensor alone. I would also need a charge amplifier. A charge amplifier is an electronic current integrator, that produces a voltage output proportional to the integrated value of the input current. This would allow me then to get the data needed to detect the leaks. A big thank you to the Swiss sales rep of Brüel & Kjaer for that information.
Might have been, that the amplifier that is built-in the Kemet sensor would have been strong / accurate enough to get the needed data.
My own sensor
Using a piezo vibration sensor for my project seemed more and more impossible and too expensive. While researching I have discovered a German company called Sensolute. They too have vibration sensor able to detect even small vibrations. Basically, it is a gold sphere in a closed sensor. If the sensor is shaken the circuit is closed and generates a signal.
The disadvantage clearly isthat you just get a Boolean signal (shake / no shake). But perhaps even with that leaks generate another signal pattern than the normal vibrations.
We will see.
With that decision made I am officially out of competition. But I do not care too much. Looking forward to see the other projects and I’m sure I will learn a lot for my own from them.
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