Tutorial 03 for Arduino: Electrical Engineering Basics Video Lecture | Arduino Programming: Step by Step (to become an Expert) - Electronics and Communication Engineering (ECE)

hey everyone Jeremy Blum here with our
third installment in the Arduino
tutorial series this we're going to be
talking about E or electrical
engineering basics this is just things
like voltage current resistance
understanding Ohm's law voltage dividers
voltage regulators things along those
lines all the basic stuff you need to
get an Arduino hooked up to some real
circuitry doing some cool stuff so for
each example I go through I'll talk
about how it relates to Arduino and an
example of when you need to use it when
interfacing some electronics with the
Arduino and it should be a lot of fun so
let's get started okay let's talk Ohm's
law I'm sobbing law you'll ever learn
about Electrical Engineering it's very
simple all it says is that voltage
equals current times resistance
resistance is measured in ohms current
in amperes or amps and voltage in volts
if you want to learn a little bit more
about current I'll refer you to Gerry
Ellsworth's video on the topic it's
really quite good so let's see an
example of this law in action let's see
we have a five volt battery positive and
negative terminals and a 100 ohm
resistor across it what's going to
happen is that currents going to flow
through this circuit but how much
current well using Ohm's law it's very
easy to determine voltage equals current
times resistance which means current
equals voltage over resistance which we
get by dividing both sides by R
therefore we can say five volts over 100
ohms as we were given in the problem is
going to give us point zero five amps or
50 milliamps of current through this
circuit in the direction shown from
positive to negative and that's it
that's all there is to it that we just
determine how much current is Fung's
that circuit okay now let's talk about a
practical application of this LEDs
everyone uses LEDs and especially in the
Arduino they're very very useful for
debugging and many other purposes so a
lot of people always ask why you can't
just hook up an LED from 5 volts to
ground why can't you just send power
through and lights up well it will light
up but we're going to run into a serious
problem here
LEDs the way LEDs work is they work on a
diode IV curve which you can see here
basically what that means that after V
drop or after a certain point what's
going to happen is the diode allows any
amount of current available to flow
through it which is
good for many circumstances but if we
want if it's in light emitting diode
we're going to have an issue because or
if it's any diode really we're going to
have an issue because we're allowing it
to draw unlimited current from the
source and the Arduino supply can only
store so much current so what that means
is this is going to suck up all the
available current and it's going to kill
your battery very quickly and the LED is
going to burn very bright but also get
very hot because you're sending so much
current through way more than it's rated
for and that will kill the LED pretty
quickly so it will let up but we're
going to run into some issues most LEDs
are designed to run with around 20
milliamps of current flowing through
them so let's see how we can design the
circuit so that the proper amount of
current is flowing through the LED which
will ensure we get a long life span and
a reasonable battery life to do that
we're going to put a resistance in line
with the LED and you always see this in
fact it is in the video last week and
here's the reason why by putting a
resistance in line with it we can ensure
that a proper current is going through
the line from 5 volts to ground and
therefore that there's not too much
current going through the LED so let's
figure out what resistance we want that
to be if we have a 5 volt supply and we
want 20 milliamps of current going
through the LED which is a pretty
standard amount for it to glow at a good
brightness will want to use Ohm's law to
figure out what the resistance should be
to accomplish that so resistance equals
voltage over current we have 3 volts
left because 2 volts will drop over the
LED on its own so that gives us 5 minus
2 which is 3 volts to drop over the
resistor so we want to drop 3 volts over
the resistor and we want 20 million s of
current to be going through it so if we
divide that out we get that the
resistance should be 150 homes and of
course you can go higher than that it'll
make the LED a little bit dimmer you can
even go a little bit lower than that but
you usually don't want to go too much
lower you'll be drawing too much current
and hurting your battery life and that's
it so let's see an example of what this
means in a natural circuit so I have an
LED here hooked across our voltage and
ground lines from the Arduino which is
running at 5 volts let's see what
happens to the current that's going
through it when I plug it in whoa 158
milliamps that's way too much that's
drawing basically the maximum that the
Arduino can output and you can even see
if the LED is growing yellow instead of
green
because the spectrum of the color has
changed do the massive amount of current
that's flowing through it let's unplug
this before we damage anything now I
have a 150 ohm resistor as we calculated
in ohms log before
hooked up with the LED in the Arduino
let's see what happens
LED turns on this time it's actually
glowing green like it should and we're
at just about 20 milliamps perfect homes
are predicted adjusted it as we expected
it to now we're going to talk a little
bit about pull-up and pulldown resistors
so if you remember in last week's
tutorial we use the button much like
this one hooked up to pin 8 on the
Arduino same as we do here but we had a
pulldown resistor between the pin on the
Arduino and ground and it was a 10k
resistor now we just have the button
hooked into 5 volts and the other end
goes right into pin 8 on the Arduino you
would think that when I push the button
down you would get the 5 volt signal in
the Arduino pin and would go to one
which it does but the issue is going to
come in when I not holding the button
and you would think it would go to 0 but
what's really going to happen is that
the pin is going to kind of float at
some random variable that can be
influenced by random electrical noise in
the area and will cause the Arduino to
get false readings of 0 and 1 and
switching back back and forth between
them if you look at the code I'm running
on the Arduino right now it's very
simple basically all it does is um we
have a button hooked up to pin 8 it's
set as an input all I'm doing here is
allowing it to communicate with the
computer via serial we'll cover this a
little bit later on in more detail but
basically it just allows us to send
information to the computer terminal and
all that I'm doing here is I'm sending
that information on a different line
each time and it's going to read the
state of the button pin and then wait
for a second
so in this terminal window right here
it's displaying each second it's
changing this value right now it's
showing a zero like it should and when I
hold down the button it's going to
change to a 1 as we would expect it to
but let's see what happens on time with
the noise so I just release the button
and it's still displaying a one you can
see it's scrolling up the screen there
and I bet yep simply just messing around
with the wire a little bit we'll
occasionally get it to turn to a zero
that's not right at all electrical
circuits should not do that
and so the reason behind that is we're
just basically causing random electrical
noise that's causing the pin to float up
and down and either go high or low
which is not what we want so let's try
this circuit now again with a pulldown
resistor in place we now have our 10k
resistor in place and essentially what
this resistor is doing is setting the
default value for the button what that
means is when the button is not
depressed the resistor pulls it down to
ground but when I push the button since
the resistance is so high to ground and
so minimal to 5 volts we're essentially
going to get a 5 volt signal on 10-8 of
the microcontroller which we can see if
we look at the screen now if I push the
button it goes to 1 just as you expect I
release the button and it goes back down
to zero and unlike before wiggling this
or touching it with my finger or
anything like that isn't going to jar it
from 0 it's going to stay exactly where
we want it to perfect and that's how
pulldown resistors work pull-up
resistors work in a very similar fashion
except they pull it up to 5 volts as a
default instead of to ground we can do
that too if we wanted to next topic is
voltage dividers so voltage dividers are
something that we're going to use a lot
whenever you're basically dealing with
any kind of analog input to the Arduino
or any other microcontroller so let's
talk briefly about how they work say we
have a 5 volt signal and we want to get
any voltage between ground and 5 volts
out of it it's very easy to do and all
you actually need are two resistors
basically you hook up two resistors
between 5 volts and ground and take a
line out between the two and based on
what you tune r1 and r2 to using the
voltage divider equation which I'll
explain in a second you can get V out to
be any value between ground and 5 volts
the voltage divider equation is pretty
simple basically all it is is the
voltage that you get out here is equal
to whatever the original voltage in this
case will be working with 5 volts that
voltage times the bottom voltage over
the sum of the two voltages so it's kind
of like a ratio you're dealing with this
over the whole thing so let's talk about
an example here let's say that we have
r1 is equal to r2 is equal to 100 ohms
so both these are 100 ohm resistors
every time when you have two resistances
of the same value in a voltage divider
what you'll find is that the voltage out
will end up equaling exactly half of
what the original voltage was let's see
why that is if we have a hundred ohms
from r2 and then these two are both 100
ohms
that's 200 ohms together that's 100 over
200 which is 1/2 times 5 volts the
original voltage which gives us 2.5
volts perfect now let's talk about a
practical application of a voltage
divider the main application of a
voltage divider is for inputs as sensors
and such as sensors and potentiometers
into an Arduino they have a lot of other
inputs maybe you need a voltage
reference there's things like that but
generally you want to use a voltage
regulator when you want to draw a high
amount of current out of them when
working with sensors or they work
perfectly so the simplest possible
example is a potentiometer the way a
potentiometer works is basically there's
a little wiper that goes back and forth
along a resistance value usually about
10k that you hook up between 5 volts and
ground so what that wiper is doing is
it's acting just like our line up here
except now there's only one resistance
and it wipes up and down between the two
changing the resistance on the top and
bottom and this essentially gives you a
voltage selector that you can then feed
into the Arduino and then used to check
a voltage so if the wipers all the way
at the bottom
it's basically connected to ground and
the wipers all the way at the top it's
essentially connected to five volts but
when it's in the middle you end up with
a voltage divider equation and I'll show
you how that works in just a moment
another example is when you want to hook
up basically any other kind of sensor to
the Arduino most sensors work as being
variable resistors so if for example we
have a photodiode which changes its
resistance along with changes in the
amount of light in the room which you
represent like that we can hook that up
their voltage divider circuit so once
again we'll have five volts a we usually
use about 10k as the other resistor and
then our variable resistor right here so
as the light in the room changes this
resistance varies which affects the
voltage divider equation this guy and we
therefore get a different voltage up so
as the line the room varies we get a
different voltage out of our line here
which then gets fed into the Arduinos
analog inputs and we can read that value
between zero and five and do something
interesting as a result so let's see an
example of this in action now here I
have a simple potentiometer usually
abbreviated to a pot and I have it
hooked up to one of the analog input
pins on the
we know now we'll be talking a little
bit more about analog input in some
future episodes but basically we have a
red connector on the pot which goes to
our 5 volts ground which goes to ground
as I shown in diagram and then the
middle one is the one going to the
analog input pin on the Arduino which is
analog input 0 the Arduino has 6 analog
inputs each of which can read values
from 0 to 1023 depending on the voltage
from 0 to 5 that you give them and you
can change the voltage reference to but
we'll talk about that a little bit later
so let's see what happens when I turn
our potentiometer you can see as I turn
the pot the value goes from 0 up to 1023
and then I can turn it back down the
other way and the reading that the
Arduino gets scales down back to 0 the
program that I'm using to do this is
almost identical to the program that we
use before except now it's a
potentiometer it's hooked up to analog
input pin 0 this is different than the
set of digital pins but it's still 0
it's still an input we're still
initializing our serial connection the
only difference really is that we're
doing an analogue read instead of a
digital read which reads the value in
from 0 to 5 volts and assigns it a
digital value from 0 to 1023 and if
you're more interested in analog digital
conversion I talked about that in the
tech bits episode which is linked below
the last thing we're going to talk about
today is voltage regulators we just
talked about a voltage divider as a
great way to get a lower voltage out of
your circuit that's providing a higher
input voltage but if you want to use
something that draws a fair amount of
current and is it using a fixed voltage
then a voltage regulator is the way to
go the reason being is that voltage
dividers will give out above a certain
output current and will start to fall
off and performance in the voltage that
they can provide whereas voltage
regulators up to a certain current are
guaranteed to always output that voltage
despite the input current as long as
it's above a certain value this is an
example of what a voltage regulator in
real life it's generally 3 pins in the
three pins match exactly these ricans
leftmost accepts a signal above about 7
volts up to 17 volts the middle one goes
to ground and the third pin goes to a 5
volt rail so what this is doing this is
taking 9 volt
in this case we're going to hook it up
to a 9-volt battery and I'll spit out
five volts and the great thing about
voltage regulators is that even as the
battery dies or as the voltage decreases
from nine volts to about eight it's
going to continue providing a constant
five volts signal which is perfect for
powering motors or anything that you
want to be at a constant voltage there
the key thing to remember when using
voltage regulators is that you always
have to use these decoupling capacitors
on both power rails the reason being is
that the capacitors essentially act as a
reservoir for electricity that holds the
excess as the voltage regulator does the
conversion from higher voltage to a
lower voltage and removes ripples and
just basically make sure that you have a
clean output voltage that's perfect for
working with let's see what happens when
we put this voltage regulator into a
circuit here we have our voltage
regulator hooked up in a circuit voltage
regulators right here note the heatsink
that dissipates excess heat we also have
two decoupling capacitors as I described
in the diagram earlier this is all
hooked up to a nine volt battery on one
end of the voltage regulator and on the
other end I have a multimeter showing
the voltage output if we hook up the
battery you can see that the voltage
goes straight up to five volts just like
we want it to and a disconnect and it
goes right back down to zero and if
regardless of the voltage level this
battery as long as it's within the
acceptable range designated by the
datasheet
we'll get always get five volts out of
here which would be perfect for powering
a lot of projects note that as this
battery discharge we'd be getting a
different voltage if we were using a
voltage divider because it would change
the input voltage and therefore the
output voltage would change accordingly
okay that about does it for this episode
of our Arduino tutorial series I hope
you guys enjoyed it as always any
documentation or anything especially
with this episode is available on my
website Jeremy boom comm there's a
description in the link below also don't
forget to head over to element14 and
submit your project to the element14
arduino contest that's running up until
January 31st so submit your project I
really look forward to seeing everything
you guys have been working on it should
be a lot of fun and that's about all I
have for this week so I will see you
guys next time 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 them
tutorials 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
talk to you about electronics the
Arduino 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