An open source electrical impedance spectroscopy system (Part 1)

Introduction and motivation

As with any start, the beginning of this project is quite different from the result that has been obtained after more than 4 years of part time research and development. The original question that ignited everything was quite simple:

As a side note, one of my personal goals for these series of publications will be to try and keep the writing professional and scientific. At times maybe a bit “scientific-paper like”, trying to avoid unnecessary anecdotes and avoiding writing on the first person perspective as much as possible. I have been trying for some time now to improve my writing skills, more specifically my scientific writing. Maybe one day, I will be able to write that cool paper I want. I will give myself some slack in the first few posts as I present the story prior to the technical details and will start the writing journey in a more relaxed environment. Time will tell if I can stick to my goal as I traverse the journey of documenting the project.

I’m an engineer, quick read about my background if you’re interested.

When I originally thought hard about that original question, I remember being confident about having the skills required to build the electronic circuit, maybe even write a program that could send the data to the internet, but what about water quality, what do we really mean by it?

I am the lucky husband of a beautiful and smart biochemist. Part of her experience in previous roles is on the quality control of water when used as a raw material for different industrial processes. One could say that I wasn’t starting at square zero with respect to what is necessary to estimate water quality.

A good friend of mine who is also the person that asked that original question and my partner on this project, had also experience on the water world. He was involved on the sales of filtering and water treatment equipment for the residential market and some smaller commercial solutions. Our discussions were lengthy and at times confusing. Sometimes just downright chaotic. My lack of confidence in the chemical science side of things was making me uncomfortable about finding a real solution to the problem.

After many conversations with my friend and my wife about what water quality really means, my engineering brain wanted something more focused and realistic. I don’t know enough about water analysis, chemistry and other important topics in order to claim I can build something that can do an irrefutable assessment on water quality.

That question was a lot better for me. Water conductivity is specific enough and well defined. Measuring its value with an electronic circuit should be piece of cake shouldn’t it? This was 4 years ago, so one valuable lesson I grabbed from this journey is that the piece of cake, is not real. Never forget that.

I was proud of being proficient with Arduino boards and writing programs for Arduino. I created an Arduino based prototype that was able to send data to a PHP server through an HTTP POST using a Quectel M95 GSM modem with a SIM card. I didn’t know much about PHP, the HTTP protocol, servers, security or much of anything related to the internet. My circuit was able to take the digital inputs of a couple toggle switches and take some analog readings using potentiometers and was able to send that data to the internet and display the data on a very basic website. I felt like I was almost 90% done.

The first Arduino Circuit Prototype.

As I wanted to add more features I quickly learned that the Arduino Uno really wasn’t for me. The microcontroller was quite small and I wanted more power. I found a different board made by a company called mikroe. They had an Arduino compatible board with more horse power than the original Arduino Uno microcontroller. They called the board the flip and click, and at the time I felt like this was closer to the solution I was looking for. I even got the new prototype with the flip and click board in what I can now proudly call the “ugliest enclosure ever”. At the time I felt like I had created the latest product in Apple’s catalog. But hey, it did talk to the internet!

My proudest moment on “Industrial Design”

A solution to send analog and digital signals to the internet with a GSM modem now worked. One of the pieces of the puzzle to solve the problem of measuring water conductivity and sending that measurement to the internet was “complete”. Even the GitHub repository for that first prototype is still up on the internet. Now I only had to figure out how to read the conductivity from a sample of water.

In the second part of these series of posts, I will write about how I was planning to read the conductivity of the water sample, how that idea did not work, and how learning about measuring water conductivity steered me towards the general direction of electrical impedance spectroscopy.

Engineer learning about the complexities of electronic design and development.