4.10. How to receive a command from a network

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From the course by Moscow Institute of Physics and Technology

Building Arduino robots and devices

193 ratings

Moscow Institute of Physics and Technology

Building Arduino robots and devices

193 ratings

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

From the lesson

Week 4

After going through Week 4, you will be able to connect your device to a network, plan its creation beforehand , control heavy loads, and power your device correctly.

4.1. Week overview0:50

4.2. Submersible pump2:02

4.3. Field transistor and relay6:40

4.4. Power supply6:47

4.5. Planning6:07

4.6. Think first7:46

4.7. Soil humidity sensor2:16

4.8. Where do web pages come from4:10

4.9. How to transmit data to a network11:35

4.10. How to receive a command from a network8:14

4.11. Finite-state automaton5:13

4.12. WaterMe program basics and switch7:18

4.13. Errors that we often encounter7:03

4.14. The longest sketch so far12:31

4.15. How WaterMe works5:20

Meet the Instructors

Алексей Перепелкин
Руководитель направления развития цифрового творчества
Центр инновационных образовательных технологий МФТИ
Дмитрий Савицкий
Научный сотрудник
Лаборатория инновационных образовательных технологий МФТИ

We have learnt to send data from Arduino to the Internet, but if we think about

the task which we had set ourselves for the realization of the WaterMe program,

te also need to run the poliv command from the Internet.

We don’t know how to do this yet, but we are going to learn it now.

I am going to change the sample sketch a bit

by adding several lines to it.

Firstly, we are going to have a test LED,

which will be turned on following the command from the network.

Secondly, I am going to create an object of the String type.

It’ll be a line, i.e. a set of symbols,

with which we will be able to perform various actions.

You are going to find out now why we might need it.

The rest will be carried out in the same manner.

I have set the LED pin as our output,

[PAUSE] and then,

after we start receiving the request

from the client,

I will add the received symbol to the

object of the String type, which I’m going to call “request”.

We are going to enlarge it in order to find the section

which is responsible for the command

issued from the website.

I’ve also transformed this line a bit,

as it was outputting a slightly

incorrect heading which made the browser

send a new request every second and refresh.

I have added the address which needs to be requested,

this is the same address that we used before. Why it’s important,

you are going to find out a bit later.

I have left everything unchanged here,

and then, after the data has been output from the analog input,

I have added these four lines.

One of them is the transmitted tag of the line break.

The next transmitted tag is the one which creates a hyperlink,

i.e. a link that redirects us to the Internet.

That’s what it looks like.

Tag A is responsible for the

address, which we are going to be using later.

In our case, I’ve just added symbols ?on to our address.

Between the opening and the closing tags,

it’s written “on”. This is the link text which we can see and which we need to click on.

Next we insert a space, and after the space, there will be one more link

where it’s written “off”. It’ll redirect us to the /?off address.

These slashes have been flickering in your eyes too much recently, I know.

Let me explain to you why we need this slash in particular or, for instance, that one.

Take a look at the line which we are sending to the client -

it is written in quotation marks.

Whatever we find inside these quotation marks will be the line itself.

That’s how we do it in coding.

If we need to transit the quotation marks too as part of the line,

we need to inform the compiler somehow that this is not the end.

That this quotation mark is now the end of the line, but it’s part of the line.

That’s why we put a “/” before it.

In other words, this is also a sequence,

just like the line break and the tabs, but it also contains a quotation mark.

We need this to make quotation marks be considered not only as the opening and the closing of the line,

but also as the content of this line.

This section is added on the page.

After we’ve terminated the connection with the client,

we shall see what information has been saved in the “request” line,

where we were adding symbol by symbol while we were receiving the client’s request.

Let’s look for the “?on” substring in the “request”

What is this “?on” exactly?

We’ve just added a link to the web page markup,

which redirects us to the ?on address.

Therefore, when the user clicks on this link, as it has been done in our request

received by the server, they will see this ?on substring.

If we find it, we will perform this action.

However, if we find a different substring, the “?off” substring, then we are going to perform a different action.

As you can see, this line is responsible for turning the LED on and off.

Now we can check how this works in practice.

I also promised to tell you why we needed to refresh the page,

but I’m going to mention this in the next fragment, really.

For now, we are going to check the command sent from the Internet.

I have connected an LED to our test device,

which will be turned on following the Internet command. I have uploaded a remastered sketch,

and now we can see that our web page looks a bit different.

In fact, we have two new links now: On and Off, so the page is refreshed more often now,

precisely every second. This is because we have changed this mysterious heading.

Let’s see what happens when I press On.

We can see that the LED is now on.

When I press Off, it turns off.

I’m going to repeat this several times.

I can still rotate the potentiometer

and change our value.

Look, I’m going to highlight the section in the location bar,

which you need to pay attention to.

I am clicking on the On link, and for one single second, /?on has been added to the address.

Same thing will happen if I press Off.

We need this mysterious heading,

refresh1url=http 192.168.0.150,

to be redirected by clicking just on the

address of the device after sending the command,

without all these slashes, or on and off.

We have now learnt to both transmit data from Arduino to the Internet and

send commands from the Internet to Arduino.

In reality, this trick with “refresh”

is not the best way to achieve the desired results.

However, if you are interested in this subject and would like to work on it,

you’ll definitely find a better way to execute this.

Let’s now return to the design of our WaterMe program.

And look again at our diagram,

where everything has already been made clear for us.

We know how to send data from Arduino to the Internet and

receive commands from the Internet, so we can add the depiction of the

router to the diagram and the Internet,

from where we get our requests and where we send our replies.

Now we are almost ready for the realization of our project,

but before that, let’s discuss how

to organize the code of our device.

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