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  • Hi and welcome

  • to another video about

  • our Arduino StaterKit

  • This is called the LOVE-O-METER.

  • This project is used to measure

  • how hot you really are.

  • Actually

  • in simple words

  • this circuit

  • is a very simple thermometer

  • that measures the

  • your body temperature

  • and visualizes it

  • on a string of LEDs.

  • So

  • let's look at how this circuit is built.

  • There are 5 LEDs on this circuit

  • that are used as an output.

  • So you can visualize the

  • temperature by looking

  • the number of LEDs that are

  • on at the given time

  • and so this is an extension to the

  • previous project we looked at

  • when we used three LEDs

  • and now we learn how to use more LEDs

  • so we go up to five.

  • But the most important part

  • about this circuit

  • is actually the sensor.

  • In this particular circuit, we use

  • a temperature sensor

  • called TMP36.

  • And

  • the interesting feature about this

  • sensor is that it's a very precise

  • temperature sensor that

  • generates a voltage

  • which is proportional

  • to the tempertature that it measures.

  • In particular this sensor generates

  • 10mV of voltage

  • for every degree centigrade

  • plus 0.5 volts.

  • So for example, if the temperature

  • in this room is 20 degrees,

  • then 20 multiply by 10mV

  • is 0.2V

  • plus

  • 0.5V, which is the

  • basic voltage that is always produced

  • at 0 degree.

  • by the sensor.

  • So when the temperature in this room is

  • 20 degrees, the sensor will produce

  • 0.7V.

  • Now we hit an interesting problem.

  • In this particular case

  • we will use a pin

  • that is able to measure if

  • the signal was on or off.

  • It was able to measure

  • if there was or there wasn't

  • any voltage applied

  • to the input pin.

  • in this particular case, the sensor is

  • producing a voltage, which changes

  • depending on the temperature.

  • So if we want to actually be able

  • to measure the temperature,

  • we need to be able to measure

  • the voltage produced by the sensor.

  • So, the digital pin

  • doesn't work here

  • because the digital pin

  • says if the voltage is more

  • or less than 3V,

  • to determine if the input is HIGH or LOW.

  • If the voltage is more or less than

  • 0 then the input is low.

  • We need something

  • that is going to be able to

  • give us a number,

  • which is proportional to the voltage

  • that is measuring.

  • Here we introduce the

  • analog inputs on the Arduino board.

  • You can see here

  • that there are six inputs.

  • on our circuit

  • called analog Pin.

  • Each one of them is able to measure

  • a voltage between 0 and 5V,

  • and it will return a number between 0

  • and 1023,

  • proportional to the voltage

  • it's measuring. So, when the

  • voltage is 0,

  • the number returned by the analog

  • inputs is going to be 0.

  • When the voltage is 5,

  • the number is going to be 1023.

  • For example for 2.5V,

  • the number returned by the

  • input is going to be roughly 512.

  • So, what we are doing here..

  • we wired up the sensor

  • in such a way that we are providing power

  • and connect to ground,

  • so we are powering the sensor.

  • And then the sensor has a third

  • leg that we connect

  • to analog input 0.

  • So whenever the temperature changes,

  • the voltage changes.

  • The Arduino uses a new instruction

  • that we are going to see in the code

  • later on called analogRead().

  • That will give us a number that we

  • can use to caculate the

  • actual temperature.

  • Let's try the circut for a second.

  • I am going to grab the

  • temperature sensor and see what happens.

  • So you can see now,

  • that the LEDs

  • are turning on

  • one after the other

  • when I touch the sensor.

  • And if I release the sensor now

  • The temperature is going to

  • slowly go back down.

  • And you will see the LEDs

  • start to turn off

  • one after the other.

  • So once we see the circuit is working,

  • we should be looking at the code,

  • and understand how we have

  • implemented this functionality.

  • So let's have a look at the code

  • for this example.

  • So if we look at the code,

  • you see some familiar

  • elements like the setup() function.

  • So let's start at the beginning.

  • We define a constant

  • called sensorPin that maps

  • the analog input 0, A0.

  • In the code here you can see A0.

  • And this one

  • allows us to

  • be able to change the input

  • pin if we want to.

  • And it gives a meaningful name

  • to that particular input.

  • So we know that the

  • temperature sensor is connected there.

  • So the code becomes more readable.

  • Then in the setup() function,

  • the first thing that you see

  • is that we are using serial.begin(9600).

  • This is a new function

  • that we have introduced

  • in this example.

  • It allows the Arduino board

  • to communicate with your computer.

  • So serial.begin() opens a

  • communication channel between your

  • Arduino board and the computer.

  • 9600 specifies the speed,

  • 9600 bits per second.

  • So this allows us for example

  • to print numbers

  • that we can read from the analog inputs

  • and send to the computer,

  • where we can use the serial monitor

  • that I will show you in a few seconds

  • to visualize the data

  • that comes from the Arduino.

  • Then we find the "for" loop.

  • The for loop is useful

  • in order to

  • execute a certain number of

  • instructions for a very well

  • defined number of times.

  • In this particular case

  • we need to set 5

  • pins on the Arduino

  • to become outputs,

  • and then we need to turn them off.

  • So instead of writing the same

  • two lines of code for five times,

  • we use "for".

  • If we look at the code,

  • We say that "for" starts

  • with x=2.

  • Then every time that we execute

  • pinMode() and digitalWrite()

  • x increases by 1.

  • x++ is the instruction

  • that increases the value of x by 1.

  • And we keep doing this until

  • x is less than 5.

  • So when we hit pin5, we stop

  • doing this loop.

  • So, this is very useful.

  • If you have to apply the same operation

  • to a number of pins.

  • So let's delve into the loop.

  • Inside the loop

  • We are reading the sensor value

  • using analogRead(), so we have

  • sensorVal = analogRead(sensorPin).

  • This will measure the voltage and return

  • an interger number

  • which is proportional to the voltage

  • that has been read.

  • Serial.print()

  • prints the number towards the computer.

  • serial.print('ADC')

  • specifies the number that

  • we just sent to the computer

  • 1s a raw value

  • from the analog to digital converter.

  • The analog to digital converter

  • is the circuit

  • inside the Arduino processor

  • that turns a voltage into a number

  • that we can use in our code.

  • The next operation

  • turns the number read

  • by the analog to digital converter

  • into the actual voltage.

  • So we specified

  • that the numbers between 0 and 1023

  • represent the voltage between 0 and 5V.

  • What we are doing here is

  • dividing sensorVal by 1024,

  • which is the number of possible values

  • that are representable by analogRead()

  • and we multiply that by 5.

  • This float variable

  • is a new type of

  • variable that we are introducing

  • with this example.

  • It is able to store decimal numbers

  • as, in this case

  • is needed

  • because we are going to get

  • voltages like 0.7, 0.8,

  • and we need to be able to

  • represent this kind of numbers.

  • Then, we follow up with

  • Serial.print(voltage)

  • and Serial.print("volts").

  • This

  • again sends to the computer

  • the voltage computed by the

  • Arduino and

  • the string "volts", to specify

  • that the previous number was

  • the amount of voltage.

  • Now, here is where we actually perform

  • the calculation of the degrees.

  • The sensor, as we said,

  • is producing 10mV

  • per degree centigrade

  • and then adds 0.5V

  • to all values.

  • So, if we look at the code,

  • we are taking the voltage,

  • we subtract 0.5V,

  • and we multiply it by 100.

  • Using this formula we convert

  • the voltage measured by the Arduino

  • into the actual temperature

  • in degrees centigrades.

  • Then we print the temperature.

  • And then we use a new function

  • called println() to write

  • the string "degrees C".

  • println() on top of sending the

  • information back to the computer

  • sends this new line

  • special character that tells

  • the serial monitor on the Arduino

  • to start printing the next line

  • at the beginning of a new line.

  • This makes sure that all

  • the value that we visualized

  • are all nicely

  • aligned and readable.

  • Finally

  • once we have the temperature,

  • we need to be able to decide how many

  • LEDs are turned on and off

  • depending on each temperature.

  • So what are we are going to do?

  • Actually, we are going to use a series

  • of "if"s.

  • In the previous example, we use

  • "if..else" to

  • be able to decide

  • when to execute one part of the

  • code or another part of the code

  • depending on the result

  • of a question, a kind of

  • condition that we ask Arduino

  • to verify.

  • In this particular case,

  • we have to verify multiple questions,

  • because we have five LEDs.

  • Therefore we have multiple combinations.

  • So we use a different kind of "if"

  • notion called "else..if"

  • So we ask Arduino

  • is the temperature less than the

  • baseline temperature?

  • If that's true, Arduino is going to

  • turn off all the LEDs.

  • If the temperature is in the

  • first band, we have an "if"

  • that's measuring if the temperature

  • is more on the certain value

  • but still less than another value.

  • If the temperature is within that band,

  • one LED will be turned on.

  • And then we have a set of "else..if"

  • that goes through every

  • combination of the values until we

  • are able to turn on all of the LEDs.

  • So in this particular code that we are

  • displaying here, we are

  • using "if..else"

  • "else..if" to divide

  • the temperature range

  • that we want to measure

  • into bands.

  • And we check to see in which band

  • the temperature falls in.

  • And we decide which LEDs to turn on

  • and which LEDs to turn off.

  • Then

  • through the last "else..if",

  • we reach

  • the end of the program.

  • Then the loop is going to start again.

  • We are going to go

  • through the same sequence,

  • measure the temperature

  • through analogRead(),

  • take the number, turn it into a voltage,

  • then from the voltage

  • compute the temperature,

  • print all that information

  • onto the screen and then afterwards

  • decide which LEDs

  • to turn on depending on the temperature.

  • If now I grab the sensor

  • the temperature increases and

  • the "if" statements are deciding

  • which LEDs

  • - for example, at this moment these LEDs -

  • are flickering, because

  • the temperature is between two bands.

  • So it's still undecided which

  • one should be turned on.

  • If I release this,

  • and maybe I

  • blow a little on the circuit,

  • you will see these LEDs will

  • start to flicker a little bit.

  • and then turn off.

  • So, we have now reached the end

  • of this example.

  • We have learned a little bit more.

  • We have learned about

  • controlling multiple LEDs.

  • We learned about reading analog inputs,

  • converting the values into voltages,

  • converting the values into temperature,

  • using multiple "if" statements

  • to divide the value into the bands,

  • and make multiple decisions.

  • And then how to print

  • all this information

  • back to the computer.

  • I hope you will enjoy

  • playing with this project and

  • I'll see you in the next video.

Hi and welcome

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Arduino視頻教程03:Love-O-Meter(愛情表) (Arduino Video Tutorial 03: The Love-O-Meter)

  • 80 2
    Chuan Zhe Lin 發佈於 2021 年 01 月 14 日
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