Welcome to another Arduino tutorial video.

Today we are going to learn

how to use Arduino

to move things in the real world.

To do that, we need to learn

how to control a DC motor

using Arduino.

The DC motor is a simple

electro-mechanical device

that you can see here.

It is normally powered

by a 9V battery

We are going to build a circuit

that will let Arduino

turn on and off this motor.

And we will be using that

to control this colour wheel

that we have manufactured

using an old CD.

In the kit, you will find parts

in order to build the wheel adapter,

and you will find the paper

that you can glue on top of the CD.

There are some issues that we have to

take care of.

First of all the DC motor here

works normally at more than 5V,

which is the standard voltage

that Arduino operates at,

and it requires more current

than a single Arduino pin can provide.

Normally, we can just hook up

a regular LED to an Arduino pin,

because the amount of electrical current

that the LED needs in order to operate

is low enough that you can power it

with an Arduino pin.

But in the case of the DC motor,

the motor requires a current

which is much higher,

and we risk burning

the Arduino pin

if we try to hook it up directly.

There is also another issue

that we have to be aware of:

when you turn on and off

an electric motor

- when you turn it off actually -

it generates a spike of

negative voltage that can actually

go back into your equipment

and destroy some of the parts.

In order to solve this problem

we are going to use a new component

that we haven't used

in the other videos,

which is called 'mosfet transistor'

This is essentially

a switch that can be

turned on and off by

applying - or not -

a voltage to a certain pin

of the mosfet transistor.

The mosfet here has 3 pins

called source, drain, and gate.

The mosfet is essentially

an electronic switch that can be

turned on or off by

applying a voltage on a pin

called 'gate'.

So this mosfet transistor

has 3 pins called gate,

source and drain.

If you apply a voltage to the gate pin

it connects

the gate and the source together,

as if I was pressing

a button on a switch,

but this is all done electronically.

So I can use this

to connect the battery

to the motor,

and since the mosfet is sitting

in-between it basically

connects and disconnects

the motor from the battery

and I can control this

through software that I

write on the Arduino board.

When you turn off an electric motor,

it normally generates

a spike of negative voltage

that can destroy your equipment.

Even if the mosfet

is quite strong

it is still very sensitive

to these negatives spikes of voltage,

so we have added to the circuit

this "flywheel diode"

that conducts

only when the motor generates these

dangerous spikes of voltage

and protects the mosfet from burning.

So what the mosfet is doing for us:

it lets us control loads that are

larger than we can

normally manage with an Arduino pin;

it lets us operate at a voltage,

which is higher

than the standard Arduino voltage.

As I said,

Arduino operates at 5V

but the battery here is 9V.

Using the mosfet allows us

to switch on and off bigger loads

that operate at voltages

that are higher than the Arduino

standard operating voltage.

It protects us,

because if something happens,

the mosfet blows up at worst,

but using the diode the way we

hooked it up here we can protect

the mosfet and we have a fairly reliable

and robust way to turn on and off,

but even change the speed, if we want,

of this DC motor.

So let's look at how

we can build this circuit.

First of all we place the mosfet

on the breadboard

and then we connect the negative

,the black wire,

of the motor right in the middle pin.

Then if you look at the mosfet

from the front,

where you can see the markings,

the pin on the left hand side

is the 'gate'.

We are going to wire it up

to pin number 9

on your Arduino.

The pin on the right hand side,

that's the ground.

We are going to

connect it with the jumper wire

to the ground rail

here on the breadboard.

Then we are going to connect

the ground from the battery

together with the ground

on the breadboard so that the battery

and the Arduino

have the ground in common.

This is a condition

needed so that

the power supply on the Arduino

and the battery have the ground in common

so that the voltages are all referring

to the same ground

and the circuit can operate properly.

So the circuit works like this.

We connect the 9v

coming from the battery

directly to the motor

and then from the motor

we connect the ground pin of the motor

to the mosfet

and then the mosfet connects to the

actual ground on the circuit.

So when the Arduino pin

turns on and off,

a 5v voltage

will be applied to the gate.

When the gate receives the voltage

from the Arduino pin, it will connect

the motor to ground

and the motor will start to spin.

When we remove the voltage

from the gate pin,

the mosfet will open

and the circuit will break

and the motor will stop running.

Let's look at the sensor part

of the circuit.

In our case the sensor

is a button, so we wire up

the circuit in the usual way.

We have a button here.

We have the resistor,

which is a pull-down resistor,

so we connect power to the button,

button to resistor, resistor to ground,

and the point where the button

and the resistor connect,

that's where we connect the wire

to take that voltage

and bring it to pin 2 on the Arduino.

Every time I press the button,

the Arduino detects that condition

and turns on the mosfet.

Here we have a motor

and here is a small adapter

which adapts the motor shaft

to this pinwheel

that we manufactured using al old CD

and a piece of paper

that you can find in the kit.

Once I created the adapter,

I am going to put a little bit of glue on it,

so that the cd is not going to

fly away the moment I turn on the motor.

Let's put a few drops of glue.

Let's try.

You can see now that it is picking up speed

and it's turning into this interesting

cappuccino colour.

If I release the button

the motor starts to slow down.

That's pretty good.

So this was our example

and now let's have a look at the code.

Starting from the beginning

we have a couple of constants.

switchPin,

that maps the switch to pin number 2,

and motorPin

that maps the motor on pin 9

Then we have a variable called

switchState = 0;

which will contain

the state of the push-button

and it will be used in an if-statement

to determine if

the motor has to be on or off.

Then let's look at the setup()

There is a pinMode(motorPin, OUTPUT);

that defines that the pin

that connects to the mosfet

and controls the motor is an output.

And pinMode(switchPin, INPUT)

that basically says that the pin

connecting to the pushbutton is an input.

Then let's now look at the main loop.

Inside the loop we

begin by reading the state of the button

by saying

switchState = digitalRead(switchPin);

This reads the current state

of the button and then places

HIGH or LOW values

inside the switchState variable.

After that we have an if-statement.

If (switchState == HIGH),

so if the button is pressed,

digitalWrite(motorPin, HIGH);

which turns on the motor.

else digitalWrite(motorPin, LOW);

This if-statement

looks at the state of the button

and if the button is pressed

we turn on the pin,

if the button is released,

we turn off the pin.

When the pin is on,

the mosfet connects

and it starts the motor.

This is all the code that is needed

to build this simple application.

Now you can

hack the software

and add more functionality.

For example if you look online,

you may be able to find some code

that teaches you how to

turn on the motor when you press once,

or if you press again it turns it off,

or to operate a toggle switch,

or you can learn

how to change the speed of the motor.

So the number of things you can do now

with this project are a lot.

Remember: build it,

hack it and share it,

because Arduino is you!