Tutorial 02 for Arduino: Buttons; PWM; and Functions Video Lecture | Arduino Programming: Step by Step (to become an Expert) - Electronics and Communication Engineering (ECE)

hey guys Jeremy plum here at the second
Arduino tutorial sponsored by element14
last week I gave you an intro to the
Arduino and a bunch of aspects of using
it and some intro programming this week
we're going to start talking about
analog outputs on the Arduino that's
done using PWM signals if you don't know
what PWM means or you're not really sure
with difference between digital analog
is I strongly encourage you to watch
this tech bits episode right here that I
did a few months ago otherwise we're
going to be working on using some
buttons we're going to control LED
brightness using those PWM signals we're
gonna learn about a little bit more
about the Arduino programming
environment we're going to learn how to
use functions in the Arduino programming
environment and a whole bunch of other
great stuff so let's get started your
best friend when working with the
Arduino or any set of electronics for
that matter is going to be a breadboard
this is the first stop for prototyping
your circuit and makes everything really
easy the way a breadboard works is all
these vertical pieces right here are
vertical rails
usually kakum to power ground and
they're electrically connected to
hallway through so if you look on the
left side for example you can see these
two rails I'll hook one up to power and
one up to ground and in the middle you
have these bigger pieces of breadboard
these are connected horizontally across
of course not connected though through
the middle and usually those from acting
integrated circuits on there so you can
connect the pins on each side of the
circuit and it's very useful for
prototyping next thing well that will be
using there are these resistors today
I'm using a 220 ohm resistor to work
with the LED because you want to make
sure that you're not drawing too much
current through it
and the other one is a 10k resistor that
I'm gonna use as a pull-up or pulldown
for the button that'll keep the voltage
level at ground when it's not pushed I
won't go into how to you how to read
resistors here but you can look that up
online just Google how to read resistor
codes it's really pretty straightforward
they're all color coded so you can tell
the the values an LED or a light
emitting diode is directional like all
diodes so you need to make sure you put
it in the circuit in the right direction
some of them have little indicators on
the plastic part this one doesn't this
one you can tell which direction is by
the length of the leads
the shorter lead is the one that goes to
ground the last thing here is our push
button the push button works by you just
basically push it down and it connects
the leads on one side so if we put our
multimeter into diode mode we can use it
to actually see that you can see why I
touch the leads together that the
reading on the screen goes to zero
indicating that there's a connection
between the probes the same thing should
happen when we connect it to both sides
of the button and we press on it so here
you can see that there's no connection
but if we keep the leads there and push
down on the button you can see that it
goes down to zero indicating that we've
completed circuit okay so let's get our
arduino wiring up with a push button so
we can start writing some programs with
it first off let's connect the ground
from the arduino and the power from the
arduino the 5 volts to rails on the
breadboard so that we can use them plug
a wire into the ground pin on the
Arduino I'll connect it to our left rail
here and now do the same thing with 5
volt line so plug it into the connector
marked 5 volts and we'll hook that up to
the rail on the right side next up we
want to hook our little switch up so
we'll put it across this gap in the
middle pop it in there just like that
and now we can go ahead and connect it
so what we'll do is we'll attach a
pulldown resistor from one of the pins
that can get connected on this side down
to ground so I'm gonna use a 10k
resistor for that the exact value isn't
really important here but it should be
relatively large I usually choose 10k or
1k so remember our ground is our left
side so I'll hook that up into ground
and all this is gonna do is make sure
that when the push button is not being
activated that its value is pulled down
to the ground now we'll connect the
other side of it
to the five volt line so that one we
push it down it goes to five volts and
sends a digital one to the
microcontroller so hook that up right
there now all we have to do is actually
hook up the same place where the
resistor is hooked into the the button
over to the Arduino so let's do that
plug one end of a wire into the side of
the button that's pulled down to ground
usually and the other side I'm gonna
plug into pin 8 you can choose any pin
you like really they can all do both
digital input and output but I'll pick
eight and that's it we can now use this
circuit to send a digital one or zero to
the Arduino okay now I'm just gonna put
our external LED on pin 13 of the
Arduino remember 13 already has an LED
on it but I'm gonna put another one in
there make sure the short pin goes to
ground as we mentioned before and just
like that you don't need to put a
resistor in here because there's already
a resistor for the internal LED on pin
13 great now that we have our circuit
setup let's write a program to control
it to start off let's just have it say
when we hold the button down and
therefore it's getting a digital one on
pin eight keep the LED on this is simple
straightforward in fact you don't even
need a microcontroller to do this but
this was a good place to get started so
let's define our variables up at the top
that we're going to use we'll have a pin
that the switch is connected to and
that's pin hate and a pin that the LED
is connected to which is pin 13 as
always we're going to need our setup
function so let's do that in our setup
function now instead of just having an
output we have an input as well so let's
set both goes just as with last time we
use the pin mode command and we have our
switch pin which is an input and then we
also have our LED pin which is an output
great that's all we need in the setup
now let's do our loop so we're going to
read the value of the switch and if it's
high we'll set the LED high and if it's
low will set the LED low it's just that
simple
so we're going to use some if statements
to do that to look at the values so if
we do a digital read of the switch pin
remember it's digital because it's just
a switch there's no analog values here
that see they're 0 volts or it's 5 volts
so if we look at the switch pin and if
that's high or if it's at 5 volts
currently we're going to make sure that
the LED is high otherwise we're gonna
make sure the LED is low and of course
doesn't matter if it's already assigned
to one of these it'll just keep it at
that our sketch is uploaded so let's see
if it does what we want
and sure enough I hold down the button
and the LED stays on great but that's
kind of boring right you can do that
without even using a microcontroller so
let's make a little bit more interesting
let's try to make it when we push the
button the LED turns on and when we push
the button again the LED turns off that
would be a little bit more annoying to
do without a microcontroller so let's
try to do that so if we're not going to
be using this system to toggle the LED
on and off the first thing I have to do
is add two new variables up here that
allow us to keep track of this state of
the system we'll make these boolean
boolean scan basically just have two
values true or false high or low on or
off zero or one they all basically mean
the same thing we'll keep track of what
the button was in the previous loop of
course it'll initially be set to low and
we'll make a boolean to keep track of
the current state of the LED so that we
can toggle it and this will allow us to
check things within the loop and set
them to what they need to be the setup
function is going to remain the same as
before we still just have do things that
were controlling but we're definitely
enough to change some stuff down here
right
the first thing where I can do is we're
no longer just check and see if it's
high we're checking to see if it is
currently high and was previously low
because that would mean the button was
just pressed so let's check for that
instead of using this if statement that
we have here now we'll still read the
switch pin and we want to see if that's
high but we want to see if that was high
and the last button was read as low
right and now what we're gonna do
instead of writing to it right here
we'll still do that later so let's copy
that down there but we're gonna write a
variable now so we're gonna use that led
on that we created before and just flip
that value so what that exclamation mark
there does is just invert it from what
it previously was and it will make it
the opposite value which is perfect
that's exactly we wanted to do we want
to switch it on or off and then let's
make sure we update our variable that's
gonna keep track of everything obviously
this is gonna equal high now because
that's part of the if statement let me
read that it was high okay otherwise
we're not going to write here anymore
like I said we're gonna do that
afterwards but we need to still set the
value of last button because we set it
here and we need to have it set so let's
set last button and that's going to
equal to whatever value we're currently
out here and you can do the digital read
just once at the top and then use a
variable to assign it but for the
purpose of this program this will work
just fine and now we're not writing it
always high right we're just gonna write
it to the value of LED on okay and that
should do it that should do exactly what
we need so let's see how that works
that's weird that's definitely not what
we expect oh that's interesting that
time it went on with the other times it
didn't okay that time he went off and
that time we went on that time it stayed
on when I clicked it something's
definitely not right here why is this
only turning on and off some of the time
if you guessed the switching that the
switch is bouncing you'd be correct
here's what a switch looks like when
it's bouncing up and down basically what
that means is with a simple switch like
this you have to worry about the signal
going up and down before he stays a
certain state whether it's pressed or
undressed so we have to write something
into our software that deals with that
so let's go do that now so let's add a
function to D bounce this switch and
software you can do this and hardware
also but we'll for now with the bouncing
software so the first thing we're gonna
do that's new is we're gonna make our
own function and it's gonna return a
boolean so I'm gonna define as a boolean
whereas these other ones don't return
anything this is gonna return a boolean
and we're gonna call the function D
bounce and will also feed it a boolean
value which in the function will be
referred to as last and this will be the
last date of the switch that will pass
it just like in the other functions that
are defined by default in Arduino you
enclose it in brackets so we just did is
we made a function called D bounce just
like digital read is a function with an
input switch it switch pin D bounce is
now function with input last and we can
now to find that first like let's make a
to more global or make another global
variable here that's gonna keep track of
what the current button value is then
I'll also be a boolean and we'll call
that current button and we need this to
use it with our D bounce function and as
before it'll be sent with a default
value of low okay and now let's fill in
this function here so the first thing
we're going to do is we're going to need
to determine what the current value of
the switches so we'll set that equal to
current and we'll do a digital read of
that switch pink okay now so what this
is doing is this is just setting the
value current to the input that it reads
from the switch pin and now we're gonna
have to compare that to the last one so
since we passed the last value we cannot
compare it and see if they're equal
that'll tell us if someone hit the
switch so if last is not equal to
current that's what the exclamation mark
means remember we'll do something so if
the switch change States first thing
we're going to do is we're gonna delay
by 5 milliseconds and what this is gonna
do is this is going to give the switch
enough time to finish debouncing but is
short enough that your finger will not
you have been released from the button
because it's basically faster than we
can move then what we'll do is we'll
read it again
this is just a very simple way to do a
deep bounce but it works quite well so
what we're doing here by reading this
again is we're waiting for it to finish
we're detecting that changed waiting for
it to finish bouncing by playing this
delay in here and then reading it again
where it's presumably had its steady
value and then we can return that value
from the function so we'll return
current and that should give us our D
bounce value and now of course we'll
have to change our loop down here to
work with that right so first thing we
have to do is actually run that function
so we'll set current button equal to the
value that's returned from that because
remember returns the current button
State so current button is going to
equal the debounce function and we're
going to pass it last button great okay
and now if last button we don't need to
read it anymore now because this the D
Bands function is doing that for us if
last button is low and current button
remember the value of current button has
been D bounced already so you don't to
worry about it is high that means
someone has just pressed the switch
which is exactly what we're looking for
so now we can still invert this like we
did before but we no longer need to
track this because the D bounce function
is taking care of that in fact we can
get rid of our else statement also it's
also taken care of in the D bounce but
what we will need to do is save our last
button here and make sure it gets set
always to the proper value and that'll
just get set back to current button once
we've set our button so that we can use
it next time and through the loop and
now this is gonna write led on as before
and that should do just what we want so
let's run that closed it goes on click
it goes off seems to work pretty
reliably it looks like our switch d
balancing function worked great job all
right so that's pretty cool but now
let's try to make the LED change
brightness when we click the button to
do that we're gonna use something called
pulse width modulation which is
basically a way of annulled emulating an
analog output for an LED or basically
any other device however
some of the digital pins on the Arduino
support that so we have to make sure we
pick one that does if you look at the
market on the board here you can see
that PWM pins are marked with a little
tilde sign and 13 the one that we
currently have the LED hooked up to is
not one of them so let's pick another
one we'll pick eleven eleven is a pwm
pin so we're gonna hook our led up to
pin 11 using the breadboard now first
make sure you unplug the Arduino we
don't want to do anything while there's
power connected top out our LED and
let's put it over on our breadboard
making sure we hook this short end into
our ground our ground is our left side
of the rail over here great so that led
is going between that line over there
and ground and now we can use a resistor
to go from the Arduino through the LED
to ground and we'll hook that over into
pin 11 making sure that we're not
shorting out any wires while we do that
okay this is gonna be a piece of cake to
fix in here first off we defined our LED
pin up here so let's make sure we change
that the pin 11 because we changed the
pin it sucked up - next we're going to
change our LED on value 4 which is a
boolean to an LED level variable so when
you're communicating with a pwm pin you
set it up as a value from 0 to 255 to
control it and that'll control the
brightness of the LED so instead of
setting it to false we'll set it equal
to zero and we'll change it from a
boolean to an integer so now this can
take on any value but we're only going
to concern ourselves with values between
0 and 255 which will set the brightness
up the debounce function can stay
exactly as it is and we're just going to
change some things around over here now
so now instead of saying flipping the
value of LED on will just increment its
brightness so we'll say LED level
instead of LED on and we'll say it's
equal to its previous value
Plus 51 I chose 51 because it's 255 is
divisible by it but you can choose any
number you want really we're going to
make sure we take care of cases above
255 but that'll work fine and that'll
give us five different increments this
will still set as before now the key
thing we're going to do here is make
sure that when we get up past 255 or
when we click one more time the LED goes
back into the off state so if the LED
level is greater than 255 because we
can't output values greater than 255
we're gonna just set it back down to
zero just like that very simple you
don't actually even need to put in
brackets because it's just one line you
can put it right after right after it
and the only thing we're going to change
here now is that instead of digital
right this is going to be an analog
right and instead of LED on we changed
our variable name to LED level and
that's it let's see how that works and
we can see as I click it the brightness
of the LED increases until I click it
and it goes back down to zero where it
starts all over again all right that
does it for this week's tutorial I hope
you guys enjoyed and you got a lot out
of it as always if you have any
questions feel free to ask me on YouTube
on hello.mat 14 on my website Jeremy
Blum comm whatever I'm always happy to
answer questions I'm gonna upload the
source code from this episode to my
website I'll have a link down in the
description below
shortly after I upload it and that's
about it
I'll see you guys next week we'll be
talking about some basics of Electrical
Engineering voltage dividers you
understanding current resistance things
like that stuff that you need to do some
really interesting stuff with the
Arduino all right sounds good
I can't wait to see you guys next week
thanks a lot for watching thanks to
element14 for helping me to sponsor this
video series they were kind enough to
provide a lot of the materials that I'll
be using to create these tutorials
feel free to go visit their website at
element14.com check out their community
which is a great place to talk a few
about electronics they already
and basically anything else engineering
related and they also have a store where
you can buy a lot of the parts that
we'll be using in these videos