The virtual laboratory experience.
By: Joaquin Jamilis
Tags: Arduino, Laboratory, Open Design, Electronics

July 2021, still living in pandemic times. The Open Design Master’s teachers have to face a virtual electronic laboratory with 40 students of whom not even the 10% have knowledge about electronics. The program included Arduino, electronic components (LED, LDR, resistors), measurement devices, soldering, 3D printing, coding, and more. What a challenge…

I was lucky to have some previous knowledge about a few topics that were going to be taught. I had to work in the University with some prototypes that were built with leds, sound sensors, and Arduino. What’s more, I work with 3D printing and own three machines, and I used that advantage to play with some of the experiments.

Getting to know Arduino

Arduino is an open-source electronic prototyping platform that enables users to create interactive electronic objects. It consists of a board that you must connect to a computer in order to program it. Arduino has one of the most basic programmable languages that makes it really easy to use without previous experience.

As we don’t possess almost any skill with this platform, we started with the basics: let’s make a LED shine.

The first step was to choose the correct resistor, a necessary component since a LED works with ≈1,5v and the board runs on 5v. In order to do so, we calculated how much resistance was necessary (R=V/I), and using the multimeter and the color coding of the components we chose 220Ω resistors.

The programming code has a three-part structure. In the first part we define the variables, this means that we will tell the board what ports will be used, and what components are they connected to. The second part, or the set up, is the initial variable setting and is the first function that the program executes. The last part is called loop, it’s the action or set of actions that will be repeated indefinitely.

The set up was done using a protoboard. It is a prototyping board that has ports connected internally to allow the connection of electronic components and removes the need of soldering or tying cables.

The result of the experiment and some other improvements:

Introducing the LDR

Each experiment was an improvement or addition to the last one done. After playing with LED’s for a while, the LDR was introduced. This electronic device, also called photoresistor, is a resistor with an oscillating electrical resistance value that depends on the amount of light that falls on it.

The idea was to apply the light of the LED on the LDR in order to change the values of the measurement by using the blinking experiment or just blocking the cone of light from the LED.

The scale

Every step taken had a purpose. The main experiment of the seminar was to create a scale that measures weight with light. Perhaps it’s not necessary to take that literally. As we learned in the previous experiment, the LDR could change the voltage value with the variation of intensity of light, so we needed to have a device that, with weight, could move the illuminating LED to achieve that purpose.

One of our teachers gave us the scale to 3D print. The design wasn’t perfect, some pieces needed to be carefully printed with the correct configuration. As I said before, I own 3D printers, therefore I was able to do this part of the experiment myself. For the printer settings I consider a high infill and a low layer height (both to make the piston stronger and to have a high-density print), a medium speed (50 mm/s) and black PLA (literally to create a blac box).

Given that I work with 3D printing, I have my machines clean and well calibrated so the results were perfect at the first attempt. It was only necessary to sand a little to erase the layer pattern and let the piston slide more smoothly.

Having all the components ready, it was time to build the circuit and test the scale.

In order to calibrate the scale we needed to use a measured weight (I used 7g coins) and correct the code. The only issue that I found in this step was that the plate was too light and the moving lid (the one that holded the led) was a little bent because of the weight, so the scale didn’t start to measure until a certain amount of coins. To correct this I had to give the plate some weight that could be measured as 0, that’s called ‘tara’.

After that the experiment was a success. I had the scale functioning with just a little error.

Measuring pressure

This one was an easy and really interesting DIY experiment. It consisted of a PET bottle with a latex finger on the finish. The principle is simple, if the air inside of the bottle was hotter than the room temperature, it would expand and the finger would come out of the finish of the bottle. On the other hand, if the inside air was colder, the finger would get back in.

This temperature change and air expansion takes some time, and an anxious person like me cannot wait until the latex finger pops out. With that mean I developed my own experiment using of course my 3D printer. The bottle was standing over the bed of the printer, and I turned it to 100° C. The rise of the temperature is much faster and the ‘effect’ more visible. The results speak for themselves.

As I said before, each experiment complements the previous one. The bottle had to be placed over the balance and upside down. Using the heat of the hands we would wait until the air expanded and the finger applied pressure on the plate of the scale, and being the scale connected to the computer as before, we would have in numbers the value of the force that the expanded air was doing.

Coding

This last experiment was a study of flexibility of coded structures. The idea was to follow a sequence of coordinates to create a structure.

The mandatory structure (or at least the one I built) was not so stable, and it couldn’t resist a light weight in any direction.

The structure I designed was built following this code: X, Y, -Z, -Y, X, Z, Y, X . And this was the result.