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!

How To Make A PCB Using A Laser Printer

When working with electronic circuits, sooner or later we feel the need to make our own PCBs to get a more functional and better looking circuit board.

I already made a video in the past to show how that could be done, for simple circuits, by drawing the circuit manually on the copper clad with a special kind of pen that uses an ink impervious to the chemicals needed to etch the PCB.

This time, I am presenting you a different technique, that allows you to draw the traces, and also the silk layer, with any of the design tools of your choice available on the Internet and the market in general. All you need to have is a laser printer. You can refer to this newer video for a demonstration of the process.

The whole process works on the concept that the printouts of the laser printers are made with a toner that has the characteristic of being able to protect the copper from the etching chemicals, like the ink from the pen in the original video. This is because the toner is made with a sort of plastic material.

Unfortunately, we cannot use a laser printer to print the masks directly on the copper clad, because the PCB boards are too thick for the printer. Therefore, we need to find a way to print on paper and then tranfer the printed ink to the copper afterwords.

This is made possible by a certain quality of glossy paper that do not allow the toner to stick permanently on its surface when exposed to heat. Even paper from magazines that are printed on glossy paper works relatively well for this to happen. However, there are specialized papers, that are designed specifically for this, which are called Thermal Transfer Paper For PCBs. A quick search on-line will give you plenty of places where you can buy it at a relatively modest price.

Once you have your PCB design ready and printed on such paper, the process to create PCBs becomes really straightforward.

First step is the transfer of the traces drawing to the copper. The copper needs to be perfectly clean, so it is always better to use a piece of steel wool to scrape away copper oxide and other dirt from the copper surface. Just move the wool in a circular fashion to remove all the particles of oxide from the copper clad and make sure to use gloves, otherwise the contact with the skin of your hands will soon oxidize again the copper.

Once all the oxide is removed, you need to deep clean the copper to remove any particle of dust from it. To do so, you can use some alcohol. Once done, let the board stand for a a while to make sure it is completely dry.

Then lay the board on the printout, making sure the copper is in contact with the drawing. Wrap the paper all around the board to make sure it will not move during the transfer process.

Once the PCB is wrapped with the paper, put it on the table copper-side up and use an iron at the max temperature, with no steam, to heat uniformly the whole surface of the paper and the pcb wrapped in it. Be careful not to burn yourself in the process, of course. You do not need to press hardly, the weight of the iron is just enough. Just make sure you keep moving the iron so that the whole surface is heated uniformly. Do that for a while, until the copper clad becomes almost as hot as the iron. Don’t worry about burning the paper. it is not going to happen. Paper burns at 451 F while the iron, even at the hottest temperature, doesn’t normally go over 400F.

Once the paper and the clad are well heated, put aside the iron and unwrap the board, making sure that when you remove the paper from the copper side you do that slowly and uniformly. The ink from the printout will now have moved from the paper to the copper.

Second step is the actual etching. Use a plastic container, fill it with some ferric chloride solution, enough to cover the whole pcb, then dump the board in the solution. Once the board is in the solution, you’ll notice that the ferric chloride starts changing color. From the initial brown color, it starts becoming darker and darker. This happens because of the copper on the board that starts dissolving in the solution.

While the etching process continues, try to agitate the solution periodically, which will speed up the reaction. A warmer room will also help. Every now and then, check the status of the board and remove it from the solution as soon as you don’t see any more copper on the surface of it.

Once the etching is completed, remove the PCB from the solution and start rinsing it immediately, to stop the reaction that would continue to attack the remaining copper on the surface.

You now need to remove the toner film from the copper traces, otherwise you will not be able to solder the components on it. To do so, use a Lacquer thinner on a piece f paper or cotton and work slowly a little bit at a time. Do this in a well ventilated area. Solvent vapors are both unpleasant to breath and harmful.

Third step is to drill the holes. It is only necessary if you use pass through components, of course. If you use surface mounted components, this step is not necessary, unless you need holes to hold in place the board.

Finally, the fourth and last step is to do another transfer, on the components side of the board, to transfer the drawing for the silk layer. The procedure is exactly the same, but this time the toner will be lay down directly on the board support, not on the copper.

You can see how this process allows you to quickly repeat the whole procedure on as many boards as you like. You just need to print multiple copies of the layouts on the thermal paper and go through the previous four steps.

Hope yo liked this procedure, and don’t forget to go watch the corresponding video, so you will see exactly how this procedure works.

Making A Small And Fast Computer Using a Raspberry Pi 4B

Converting the Raspberry Pi to use a SSD or a Hard disk via the USB V.3 connector, instead of the microSD card, allows for a big increase in the speed of the device. The conversion can be done very easily with an RPi 4B, since it already has the capability of booting from a USB-attached storage device, but can be easily done also to older RPi versions with a simple modification to their firmware, following the procedure on the RPi official web site.

The conversion consists in removing the microSD card from the RPi and use instead a hard disk. And for that, I bought on Amazon a nice Samsung 500GB external solid state disk for a very reasonable price. Since it connects through a USB v3 cable, it seems perfect for the job.

If you need a SSD like this, or a different one, you could use my affiliate link to buy one, so you will indirectly support this site and the eleneasy YouTube channel at no extra cost to you. You can also watch the video where I show you how to make the conversion.

And since I now have two devices, the RPi and the SSD, that need to stay connected and work together, I decided to 3D-print a nice box to save some desk space.

There are two parts: one for the actual box and one for its cover. They are both made out of a simple cube, but I made a few slits on the bottom of the box and on the cover to help with the air flow, so the components inside will not overheat, especially the RPi.

Here is the OpenSCAD code I used to design the object:



	cube([100, 100, 65]);
	translate([2, 2, 2]) cube([96, 96, 64]);
	translate([1, 1, 63]) cube([98, 98, 3]);
	translate([5, 20, -1]) cube([88, 2, 4]);
	translate([5, 34.5, -1]) cube([88, 2, 4]);
	translate([5, 49, -1]) cube([88, 2, 4]);
	translate([5, 63.5, -1]) cube([88, 2, 4]);
	translate([5, 78, -1]) cube([88, 2, 4]);
	translate([2, 97, 20]) cube([15, 4, 20]);

	translate([35, 97, 10]) cube([56, 4, 20]);
	translate([97, 8 , 10]) cube([4, 70, 15]);


translate([110, 0, 0]) difference()
	cube([98, 98, 2]);
	translate([10, 20, -1]) cube([78, 2, 4]);
	translate([10, 34.5, -1]) cube([78, 2, 4]);
	translate([10, 49, -1]) cube([78, 2, 4]);
	translate([10, 63.5, -1]) cube([78, 2, 4]);
	translate([10, 78, -1]) cube([78, 2, 4]);

Pleass refer to my YouTube video for the details of the project.

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