2.7. Reading off digital signals

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來自 Moscow Institute of Physics and Technology 的課程

Building Arduino robots and devices

149 個評分

Moscow Institute of Physics and Technology

Building Arduino robots and devices

149 個評分

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

從本節課中

Week 2

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.

2.1. Week overview1:16

2.2. First sensor1:56

2.3. Voltage divider5:19

2.4. How to read off analog signals5:30

2.5. Exchanging data through a serial port6:44

2.6. About a signal8:45

2.7. Reading off digital signals5:37

2.8. Boolean expressions and program branching16:43

2.9. New display devices: buzzer and bar graph13:12

2.10. Seven-segment display2:24

2.11. Microchips4:25

2.12. Output shift register13:21

2.13. Debugging5:37

2.14. Usage of modules6:19

2.15. Monitoring system12:01

與講師見面

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

Let’s try to evoke the difference between a digital and an analog signals.

The analog signal was examined at the beginning of Week 2.

When we started the visualizer, we saw

the signal change swiftly: the value was changing from 0 to 5 V.

The digital signal can either be present or absent:

it will either take the value of 0 or 1.

In Arduino pin terminology, this is either High or Low.

This means that when we record a digital signal, we write digitalWrite (high)

and we put the value of 5 V at the specified output.

And when we write digitalWrite (low), we set the value of 0 V at the output.

Now we are going to learn how to read off digital signals:

we will also try to determine whether or not there is voltage at the input.

While reading off the signal, the controller will be determining

whether current voltage is higher or lower than 3 V.

Thus, the “low” or 0 value will be assigned to anything lower than 3 V, while

the “high” or 1 value will be given to voltage higher than 3 V.

Now we are going to prepare a sketch to experiment with.

In this experiment, we will be transmitting everything that is passed to

input 7 directly to the in-built LED and output 13.

To make an input and an output out of the 7th and 13th pins respectively,

we shall start with the pin mode function designation in setup.

For LED_PIN, pin 13, this will be “output”,

and for DIGITAL_IN, pin 7, this will be “input”.

Our loop will consist of recording the digital signal

on LED_PIN leaving it in the same state that our DIGITAL_IN pin is now.

Now we need to receive this digital signal at input 7.

For this purpose, we shall assemble a simple circuit.

A simple tact switch will help us receive this signal at input 7,

the same switch we used

during Week 1 to manually control a traffic light.

At one end, I have connected it to the 5 V Arduino output with this red wire,

and at the other end, I have used this white wire to connect the switch to input 7.

Consequently, when the tact switch is on, the 5 V voltage will be transmitted to input 7.

We will determine high voltage level and will transmit the signal to output 13.

Let’s try and see if this works.

Yes, it really does work.

I am now going to say a couple of words about the resistor which I connected at the same end

that has a wire connection with Arduino.

This is the so-called pull-up resistor.

It is connected to the “ground” link on the breadboard which, in its turn, is connected to Arduino’s “ground” link.

We need the resistor in order to prevent the switch from picking up any noise that always exists on air.

I can remove it from the circuit, and we shall see

that the LED is on when the switch is off.

When I press it on, it will be brighter, but during the rest of the time,

input 7 will be receiving voltage which

is perceived by the controller as high, so the LED will also be on.

Now let’s look at the sketch again: I am suggesting an alternative

to get rid of the noise on air.

We shall configure the output destined for the switch and marked as DIGITAL_IN,

not into a simple INPUT, but into INPUT_PULLUP.

What is it exactly?

It turns on the pull-up resistor which is built in Arduino,

although in this case the pull-up is performed towards the voltage supply and not the “ground” link.

Some people separate the terms of “pull-up resistor” and “pull-in resistor”,

but I’m used to calling it a “pull-up resistor”, as it pulls the switch up either towards the “ground” link or the voltage supply.

As a result, the INPUT_PULLUP pulls the switch up towards the voltage supply.

To make it work, I have set the second output of the switch

from 5 V to “ground”.

And now, look how the LED is on when the switch is off.

Thus, when the switch is off,

high voltage exists at the input because of this INPUT_PULLUP function.

When we press the switch on, the voltage disappears,

therefore, the switch operates vice versa.

This method is more convenient, in my view,

as it simplifies the scheme. Moreover, we can get rid of all this input noise

by changing only one single parameter.

To conclude, we have learnt to read off a basic digital signal.

Why do I say “basic”?

All digital devices that surround you

communicate with each other in a more intricate manner

than just through “yes” or “no”, “signal” or “no signal”.

They use pre-agreed communications protocols,

where it is discussed and agreed in advance what the combination of

high and low voltage levels in certain periods of time signifies.

We will later have to deal with sensors

which use complex protocols, but this will happen over the course of the upcoming weeks.

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