The Turbidity Tester

Plastic and other garbage in the waters has become a real issue in recent times. To make a difference in the effort of keeping clean the world in which we all live, thousands of YouTube creators have teamed up, lead by Mr. Beast and Mark Rober, to create the #teamseas global campaign, with the goal to raise $30M by the end of this year 2021 to remove from the waters of rivers, seas, and oceans all over the world, an amount of 30M pound of plastic and other garbage. One pound for every dollar.

To do so, #teamseas is partnering with the non-profit charities Ocean Conservancy and The Ocean Cleanup. They pledged to remove the 1 pound of plastic from seas and rivers for every dollar we will collect through the #teamseas effort.

To increase the awareness on this issue, today today I present you a device that can give you an idea of how many pollutants are contained in a sample of water. A corresponding video is also available here.

Here is the schematic of the device, which I named Turbidity Tester.

The sensor that measures the particles dispersed into the water is made of an LED and a photoresistor, on the bottom left.

The photoresistor I used is more sensitive to the green light, and so I used a green LED to make the circuit work at its best.

When the LED shines its light directly on to the photoresistor, the resistance will drop to a minimum, causing the voltage at the non-inverting input of the op-amp to reach a very low value.

When the LED shines its light through a sample of water, the more the water is polluted, the less light will hit the photoresistor and, therefore, the more its resistance will increase, which will cause the voltage at the non-inverting input to raise. The more pollution, the more voltage.

The op-amp is connected in a non-inverting amplifier configuration, and the gain of such amplifier depends on the resistors R3 and R4, which I selected in such a way that I can have on the output of the op-amp a voltage in the range between 0.3 and 8 V.

This voltage is applied to the input of the LM3915, which is a bar graph VU meter driver, configured through the resistors R1 and R2 to work exactly within the same range of 0.3 and 8V.

This way, the VU meter will light up one of the LEDs depending on the amount of pollutants in the water sample.

For the VU meter, I used LEDs of different colors: a blue one for clean water, then green, for less that clean , than orange for dirty water and red for really bad water.

To be able to put a water sample between the LED and the photo resistor, I 3D printed this simple device.

The LED is inserted in one of the side holes, and the photo resistor on the other one, so they will face each other.

The big hole on the top is made of a size that fits perfectly a tic-tac candy container, which will hold the water sample. But of course, if you want to try this project, you can use any kind of transparent container. Just adapt the size of the chamber to fit it snugly.

So, to test some water, we fill the container, we insert it in this sort of chamber, then we power up the circuit, and we take our reading on the VU meter.

This of course is not a device that can take actual measurements of the quantity of pollution in the water, but is an example on how such measurements can be done. Using more sophisticated photo-resistors that can detect different light wavelengths, we could build, using the same principle, a spectro-photometer, and we could tune it up to have precise numerical readings for each frequency. This would enable us to determine not only the presence of pollutants, but also their chemical composition and their quantity.

And talking about pollutants, don’t forget that you can help making Earth a better place to live in by donating to the #teamseas campaign.

Once again, #teamseas is a global campaign to raise $30 M to remove 30 M pound of plastic and trash from our oceans, rivers and beaches. It’s also the second wave of the largest creator-led fundraising campaign to ever hit the internet: #teamtrees. We launched #teamtrees in 2019 with a goal of raising $20M to plant 20M trees and we smashed it, raising over $23M and generating more than 1B video views. Even after two years, is still receiving donations for planting 2600 trees every day.

#teamseas has partnered up with Ocean Conservancy and The Ocean Cleanup. All donations to teamseas will be split by the two charities 50/50.

Let’s repeat together the success we made back in 2019. Let’s help the world where we live to flourish again.

And finally, here is the archive with all the files for this project:

Happy Experiments!



I am an old school electronics engineer, but I worked almost forever doing software development for the big telecommunication companies suppliers. I have recently decided that it was time to start digging into my old knowledge and make a hobby out of it. I have several subjects in mind that I would like to explore: robotics, electronic musical instruments, home automation, and so forth. Let’s make this journey together! We can surely learn a lot of new things from each other. Drop me a comment! I look forward to hear your thoughts!

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