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2.4. How to read off analog signals

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2.4. How to read off analog signals

It’s time to learn how to receive data with the help of sensors. During Week 2, we will teach you how to read off digital and analog signals, exchange data with a computer, create more complex algorithms, and use new output devices.

For many years now, people have been improving their tools, studying the forces of nature and bringing them under control, using the energy of the nature to operate their machines. Last century is noted for the creation of machines which can operate other machines. Nowadays the creation of devices that interact with the physical world is available to anyone. Our course consists of a series of practical problems on making things that work independently: they make their own decisions, act, move, communicate with each other and people around, and control other devices. We will demonstrate how to assemble such devices and programme them using the Arduino platform as a basis. After this course, you will be able to create devices that read the data about the external world with a variety of sensors, receive and forward this data to a PC, the Internet and mobile devices, and control indexing and the movement. The creation of such devices will involve design, the study of their components, the assemblage of circuit boards, coding and diagnostics. Along with the creation of the devices themselves, you will perform visualization on a PC, create a web page that will demonstrate one of your devices, and figure out how an FDM 3D-printer is configured and how it functions. Besides those keen on robotics or looking to broaden their horizons and develop their skills, the course will also be useful to anyone facing the task of home and industrial automation, as well as to anyone engaged in industrial design, advertising and art. The course does not require any special knowledge from the participants and is open even to students of upper secondary school. Programming skills and the level of English allowing to read technical documentation would be an advantage, but this is not obligatory. The entire course is dedicated to practice, so the best way for you would be to get hold of some electronics, follow the illustrated examples and experiment on your own. The kits can be purchased here: kits.cyberphysica.ru. Taught by: Alexey Perepelkin, head of Robotics department in the Laboratory of innovative educational technologies at MIPT Taught by: Dmitry Savitsky, researcher in the Laboratory of innovative educational technologies at MIPT

Skills You'll Learn

Electronics, Computer Programming, Arduino, Robotics

Taught By

Алексей Перепелкин
Руководитель направления развития цифрового творчества
Дмитрий Савицкий
Научный сотрудник

Transcript

First, let’s try to visualize analog signals

which reach Arduino input.

For this purpose, special devices called oscilloscopes are used,

but we are not going to connect our circuit to it. Instead, we will just imitate the way their program works.

To accomplish this, we are going to make use of an outstanding tool called Processing,

which you will be studying in detail next week.

For now, you can download it following the link in the Additional materials section,

as well as download the program which I wrote to visualize analog signals.

Start Processing, open my program and take a look at the line

where the port is mentioned, to which the controller is connected.

You need to do it in a way so that its number corresponds to the actual port number

that you can see in your system.

Also, have a good look at this number – this is the connection speed.

It should correspond to the speed mentioned in the AnalogReadSerial sketch,

which you downloaded at the beginning of the experiment.

Don’t worry, we are going to speak about the connection speed in detail in the next fragment.

For now, you should just pay attention to it when the program starts.

After that, you can start the visualizer by pressing the “Run” button.

We can see a window like this, which is empty at the moment,

because the potentiometer is set to 0.

Now I am going to rotate it, and now let’s look

at this line,

which corresponds to the change of the voltage at the analog input.

Since the potentiometer covers the whole range,

we have witnessed changes from 0 to 1023.

Apart from that, I have activated the display of the minimum and maximum

observed values. This might come in handy when you study the voltage range

communicated by various analog sensors.

Looking at this picture, you might have already understood that the input voltage

changes unstoppably, meaning that at some point it can take the value of,

let’s say, 2,8327 V.

This value can be brought to further precision, but for some reason

we only saw numbers from 0 to 023 on the screen.

The thing is that when the signal reaches the controller,

it undergoes certain changes.

It passes through an analog-to-digital converter, aka ADC.

If I try to explain the way the ADC works in simple terms,

it will be as follows: a special device known as a comparator,

can compare current voltage with some base voltage

and communicate whether it has got 0 or 1 as a result of this comparison,

and whether current voltage is higher or lower than base voltage.

In case with a 10-bit ADC, this happens 10 times,

and we get a combination of 10 ones and zeros which,

after being converted to a decimal number, display the value from 0 to 1023.

As a result, the range of 0-5 V, which we can communicate to

Arduino input, can be divided in 1024 units.

In other words, the difference in units means that the voltage difference is approximately 0,005 V.

In fact, it is a bit lower.

Thus, we have a certain number at the input.

But how do we work with it in a program?

How does it appear there?

Let’s have a look.

Let me bring you back to the example

with which our experiment began — the one from the sketch template called AnalogReadSerial.

You might have already realized that

the function analogRead is responsible for reading off the analog signal.

This is another Arduino integrated function

which is designated to read off analog signals.

It receives only one thing as a parameter, which is pin number.

Let me remind you that you can refer to analog inputs

by using their board indications: А0,

А, etc. All these notations are already built in the Arduino library.

Please, take note of the fact that The analogRead function can be called to the right of

the assignment operator, while to its left appears the name of the variable

which is set here – the integer variable sensorValue.

Last week we already learnt how to create int-type variables.

However, here I would like to point your attention to the fact that when we want

to read off values from a sensor, we have to use these values somewhere.

In our case, we are going to save the value into a variable.

You can also communicate it as a parameter to another function

or use it in your calculations.

Many times I have noticed how beginner Arduino amateurs

are simply trying to call the analogRead(A0) instruction when they want to read off data from a sensor.

In reality, the controller possibly reads something,

but the value that it gets, cannot be found anywhere.

This is why, when you read off values from sensors, do try to understand

where they go.

[PAUSE] The next thing

that we will have to figure out, is how exactly the data

is communicated to the computer screen, and how we can read it from there.

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