Introduction: Side Project: Water Purity Tester

This project was a part of my curriculum in my Principles of Engineering class with Ms. Berbawy. She allotted us each with a budget of $50 to come up with a reasonable project proposal, something that would be achievable, yet challenge our abilities.

This project is based on this model from It measures electrical conductivity of a liquid and plays a sound based on the conductivity. The louder the sound the more pure the water. This is based on the concept of a voltage divider. The more conductive the sample, the more voltage gets drawn towards the upper part of the circuit, away from the speaker. This causes the speaker to receive lesser voltage decreasing loudness of the sound it produces.

The Arduino serves as a medium between the circuit and the computer where the readings are captured. This project was inspired by a recent project I had done in a class that was introduction to Arduino and bread boarding. As a step forward to challenge myself and apply the concepts that I had learned, I endeavored to make this more complicated project.


Step 1: Building the Circuit.

The first step is building the circuit. The circuit used for this build was initially quite daunting for me due to its complexity. Before touching the physical circuit it is better if you can make a simulation or some sort of mapping of your components on a virtual breadboard which would make it easier for you to make the physical circuit. For this purpose I used TinkerCAD. The easiest way to break down the circuit is by dividing it into 2 main sections: The upper section around the LM741 chip and the lower section around the 555 timer and the speaker. Initially temporary jumper wires were used in the project as they were easy to move around and handle. These were later replaced with the straight jumper wires in the final project. This makes it easier to troubleshoot and keep track of the elements in the circuit. This phase took the longest amount of time, and was not completed until almost the very end of the project.

Step 2: Adjusting the Circuit (Fine Tuning)

Once the rudimentary circuit was completed, finer adjustments still needed to to be made. The potentiometer needed to be calibrated so that the sound produced by the speaker is neither too faint or too loud. As mentioned previously, this is the step where the temporary wires were changed to the permanent ones which were present in the final circuit. This took quite some time due to the sheer number of wires used. The wires to the speaker were also clipped to make the contraption connecting the speaker to the breadboard as small as possible. Additionally to improve the aesthetics of the circuit as well as reduce the possibility of breakage the resistors and the LED were clipped.

There was a plan to also integrate a loudness sensor to measure the loudness of the sound produced by the speaker. The sensor would be originally connected to the Arduino Analogue port. An Arduino program would then be created for the sensor to pick up readings. This idea was later scraped as the sensor did not work as intended and was replaced with a computer which would pick up readings via microphone. This is not ideal, as a computer is large and bulky, but it was the best option.

Step 3: Testing Phase

This is one of the most vital stages in the life of any project and can sometimes be very annoying. Spotting problems in a circuit like this one can be very time consuming and frustrating. In this scenario using an LED can be very useful. Putting an led in the part on every individual series element can be used to test if current is flowing through that part of the circuit.

This phase was the time during which most of the major changes to the project were made. Changes like including a 5V input instead of a 9V input was one of the changes brought about during this stage. The input of 9V was creating a very loud sound from the speaker. By changing the input of power to 5V from the Arduino, worked much better.

Step 4: The Box

This part of the project was for aesthetics and to make it more compact and easy to handle. This step in no way had any effect on the functionality of the project. The box is constructed out of cardboard, with the top and one of the side s left open for sliding the components in and out with ease. This was done keeping in mind, that the Arduino cable has to be able to be attached to the circuit easily. Additionally this design also makes the circuit more visually appealing. I should have made a laser cut box out of wood, but ran out of time in the classroom because of Covid-19.

Step 5: Credits

This project would not have been possible without Ms. Berbawy who provided the funding and materials for this project to happen. I am additionally grateful to Sven and David who helped me in the course of making the project by giving helpful advice and instructing me on how certain parts worked.