Tutorial 05 for Arduino: Motors and Transistors Video Lecture | Arduino Programming: Step by Step (to become an Expert) - Electronics and Communication Engineering (ECE)

hey everybody Jeremy Blum here with
episode 5 of our element14 Arduino
tutorial series today is the last day of
the Arduino contest that we're running
so we'll let you know the results of
that really soon too then talking about
motors and transistors and a couple of
new programming topics that we haven't
covered yet like for loops we're going
to use a DC motor and change its speed
dynamically using a transistor and some
code from the Arduino and then we're
also going to use a servo motor that you
can control with PWM or pulse width
modulation signals from the Arduino
control its position and then we'll
finish up this episode by making a
little project that controls the precise
degree rotation of a servo motor using
the readings from an infrared distant
sensor let's get started today we're
going to be using an NPN transistor you
can see an example of one here NPN
transistors have three pins a collector
a base and an emitter you can see in the
schematic that it also has three pins
here collector base emitter you can
think of it like this current flows in
through the collector and out through
the emitter but it's only allowed to
flow through based on the state of the
base pin more current is allowed to flow
through from collector to emitter as the
voltage of the base pin increases on PNP
transistors the opposite of NPN
transistors it's the opposite when this
goes low the base current is allowed to
flow from collector to emitter in this
project we'll be sending a PWM or pulse
width modulated signal into the base
which will change the amount of current
flow that goes from collector to emitter
and therefore change the speed of a
motor that's hooked up to this
transistor the reason you use a
transistor to control motor is because
it helps isolate the motor from the
Arduino and allows us to draw more
current than the Arduino can provide on
its own it also allows us to operate it
at nine volts instead of five volts
which allows us to run the motor faster
here's what our circuit will look like
for controlling a standard DC motor here
we can see our NPN transistor again we
have a motor connected between the
collector of the NPN transistor and nine
volts on the base we have
1k resistor connected from the base of
the transistor to pin nine of the
Arduino which is capable of PWM control
pin 9 will send pulse width modulated
signals through the 1k resistor to the
base we put in a 1k resistor here to
isolate it from the nine volt signal
just in case something shorts out we
don't have to worry about it breaking
the Arduino as the signal on pin nine
goes up and down different amounts of
current will be allowed to flow from
nine volts through the motor down to
ground when base is high current will
flow through the motor and allow it to
turn we also add a capacitor 1 micro
farad and a diode pointing from the
collector to 9 volts to help protect us
from noise and spikes that are generally
created by motors here's the circuit all
wired up let's take note of a few
important things here you can see the
transistor the capacitor and the diode
that I talked about earlier that will be
controlling the motor this is the 1k
resistor that connects between the base
of the transistor and pin 9 of the
Arduino the most important thing to note
here though is that you always connect
all the grounds between all of your
voltages I've used this binding post
right here to connect the ground from
the 9-volt battery to the ground from
the 5 volt signal of the Arduino this is
to ensure that everything is operating
off of the same reference level now
we're going to write a quick program to
test our new DC motor circuit I've
already gotten the framework set up we
have a motor pin connected to pin 9 and
that pin is going to be configured as an
output in our loop sometimes I like to
make comments that explain to me what I
want to do on the loop before I actually
do it in plain English so that I know
where I'm going this is just a generally
good programming tip so the first thing
we're going to do is accelerate the
motor from 0 to 255 so they'll show us
at changing speeds there I'm going to
hold it as top speed for a little bit
then decelerate it down from 255 back to
zero hold it at 0 for a little bit and
then will repeat the whole thing so the
motor will accelerate then decelerate
and then repeat now to accomplish this
we're going to use a new programming
tactic called a for loop so let's get
that written up and then I'll explain
how it works
so here's the framework for our for loop
basically what we're doing is we're
defining a new integer called I that
we're going to start at zero and we're
going to increment I by one one
increment every time we go through the
loop up until we hit 255 so this will
give us 256 different points of
resolution which is exactly how many
were able to get out of an analog output
from the Arduino and so we'll do with
each increment we can use the eye on
that time through the for loop to set
the speed of the motor and we can do
that using analog right motor pin eye so
instead of sitting a number here we're
setting it to whatever the value of I is
on this time to the for loop so the
first time it goes to the for loop I
will be equal to zero and the motor
won't move on time 100 or 101 through
the for loop it I'll be equal to 100 and
it will set that value to 100 so the
motor will be moving at about half speed
and by the time we get up to 55 the
motor will be running at full speed now
we don't want to go through this too
fast
so we'll edit delay of 10 milliseconds
there so it hangs on each value for just
a little bit not even enough to notice
for a human but it'll make it seem like
more fluid motion ok and then we'll hold
it at the top for a little bit so to do
that we'll just use a standard delay
function for a half second and now we're
going to do the same thing but in
Reverse to decrease it from 255 down to
zero so again we use a for loop we can
reuse the same variable it doesn't
matter since these two for loops are
completely separate from each other so
I'll just use the I again but this time
we're going to start it at 255 and have
it go down until it is equal to 0 and
each time instead of incrementing it's
going to decrement which we use a double
minus sign to denote just like we use
double plus sign to denote incrementing
always goes in brackets and we'll do the
same thing as before
then I give it a delay of 10 and then
hold it at zero for just a little bit
with a delay of a half second perfect
let's see how this works so it's
programmed and the motors giving exactly
we want it to it spins up and then spins
down and accelerates and decelerates
just like it should
great so our transistor circuit is
working perfectly if you want to change
the direction of a DC motor
you can either swap these wires or use
an H bridge to change the direction of
current flow automatically when I use an
H bridge in this tutorial but we'll
probably use one in the future it's a
simple integrated circuit that you can
buy that allows you to run a DC motor in
both directions easily now we're going
to control a hobbyist servo motor like
this one servo motors are much different
from DC motors instead of just giving
them a constant voltage in watching them
rotate forever
servo motors respect the PWM signal
depending on the value of the PWM signal
the server will rotate to a particular
location in the case of this servo and
many hobbyist servos this one is limited
to 0 to 180 degrees based on the value
sent it will rotate to an exact
predetermined position this is really
useful for a lot of projects servos take
up a fair amount of current and you
could power one off of the Arduino has
built-in voltage regulator but if you
want to power more than one it's
generally a good idea to put it on its
own 5 volt circuit so that's what we're
going to do here just for the purposes
of demonstrating like we did last week
we're going to use a voltage regular
like this one always be sure to use your
decoupling capacitors the datasheet
specifies for this voltage regulator
that you should use point 1 micro
farad's and 22 micro farad's the exact
value isn't important just keep it in
the general area well feed in 9 volts
from a battery on one end and we'll be
making a new 5 volt rail that we can
power the servo off of on the other when
you're drawing schematics you don't
necessarily have to connect all the
wires here I have 5 volts and then I'm
calling this 5 volt rail number one you
can see a little subscript one there
that same 5 volt rail is the one that
connects to the servo over here I have a
separated 5 volt rail for the Arduino
that it's running on note that the 5
volt rail should not be connected
together
however all grounds in a circuit should
be connected together everything with
this symbol the ground symbol in the
schematic should be wired together at
some point the servo has three wires a
five volt supply wire a ground wire and
a communication wire this communication
wire operates at a 5-volt logic level
and be clean and can be connected
directly to a PWM enabled pin of the
Arduino we're going to use pin 9 again
here we can see the circuit all wired up
you can see the servo motor here it has
three wires the yellow wire goes to pin
9 on the Arduino the red wire goes to
it's 5 volt supply and the brown wire
goes to ground
note that I've disconnected the 5 volt
wire from the Arduino from the board the
2 5 volt lines should not be connected
together because they're from different
supplies the grounds however are still
connected through this lug you can see
the two decoupling capacitors here and
our 9 volt to 5 volt voltage regulator
right here that's going to be powering
the servo we have a 9-volt battery
hooked up to it now let's program it
using the Arduino servo library so we
can get this servo doing something
interesting the Arduino programming
environment has several libraries that
you can use that make it easier to
interact with different types of
hardware one of these libraries is a
servo library which we'll be using today
to interact with our servo and make
telling you what to do a little bit
easier the first thing you have to do is
include any optional libraries that you
want to use so we'll include the servo
VH library you can learn more about all
the libraries available to you on the
Arduino DCC website after we include the
files that will allow us to interact
with the servos we'll need to make a new
servo object that we can control to do
that you type servo and then whatever
you want to call the servo I'll call
this one
Jeremy is servo this is creating a new
object called Jeremy servo of type servo
now we can do stuff to that I've already
set it up as a servo on pin 9 like we
always do note that you don't need to
set it as an output manually because
when we attach the servo through the
program right now it'll take care of
that for us so we can say Jeremy's servo
dot touch
and then the pin that it's connected to
is the argument for that function and
you notice that this is similar syntax
to the serial communication function
that we were using earlier
that's because serial it's also a
library that Arduino uses although it's
included by default whereas with the
server library you have to include it
manually okay so we have our server will
attach to the program and ready to use
let's make a program that will increment
the servomotor about 20 degrees on an
incremental basis and then rotate it
back to zero again we'll use our friend
the for loop which we just learned about
earlier we'll start at 0 and the server
library takes care of all the PWM
commands that you need to send it so it
makes this really easy what this for
loop will do will start us out at 0 0
degrees and it'll rotate it goes up by
20 degrees until we get to 180 degrees
and then when we're done it'll rotate
automatically back down to 0 the library
automatically handles figuring out what
direction has to rotate into based on
the current position and what position
you want to go to so we'll call Jeremy's
servo dot right and this will tell it
the position to go to and we'll send it
to position high because we want to send
it to whatever position high is in the
for loop right now note that while
before we were incrementing by 1 we can
use this command to increment it by 20 H
time and we'll keep it at each spot for
one second just so we can see what it's
doing clearly all right good
let's see I this works ok so we can see
that every one second the servo rotates
by 20 degrees just like we asked us to
and when it's done it automatically
rotates back to 0 so it's able to
determine automatically what its range
is and what direction to rotate in to
get back to whatever position you sell
to and it's just that simple in fact we
can actually see as the servo is kind of
walking along our breadboard a little
bit here ok we're going to finish up
with a project that will allow us to
control the position of the servo motor
using the map function that we learned
in the last episode and the infrared
distance sensor that we used in left
so so let's get working on this project
adding our infrared distance sensor to
the circuit will be pretty easy
everything else stays the same we just
add our infrared distance sensor here
connected to the common ground you
should however make sure that you
connect it to the five volts from the
Arduino not the five volts so using the
power the servo this is because you want
to be off the same reference voltage
that the Arduino uses it for it's analog
to digital conversion and then look
connecting to an analog input zero on
the Arduino let's set the infrared
distance control to our program now this
will all stay the same we'll have to add
another pin definition here in distance
pin equals zero
Joey stairway will stay as it is this
can all stay the same we don't define
this input because it's an analog input
and that's the default we can get rid of
our for loop across will no longer be
using that we can get rid of the delay
now what we need to do is put in here
function for reading from the infrared
distance sensor so we'll make a new
variable called dist do an analog read
of the distance pin and then we'll make
sure that we map that value remember
that value comes in between zero and a
thousand twenty three so we're going to
map that value to a new variable called
pose position for position and 0 to 1023
will translate to zero to 180 because
that's the degrees of rotation for our
servo motor and then we'll just have
that value turn the motor so we'll set
the position of the motor with the
position variable and that's it let's
see how that works
all right the program is not running
let's see how it works
all right great you know so servo is a
little bit jerky
that's because the value is coming from
the infrared distance sensor are not
perfect they vary back and forth with
each reading you can fix this either by
adding a filter on the input or by doing
some math in the program I'm not going
to cover either those right now but if
you want to look them up you can they're
pretty straightforward we'll probably be
using some filters to handle analog
inputs in future episodes but for now
this is good enough and it's pretty cool
huh all right awesome
that does it for episode 5 of my Arduino
tutorial series and it's also the last
basic tutorial that I'll be doing so at
this point we've covered all of the very
basic things that you need to get in
order to know up and running the coming
tutorials will be slightly more advanced
and we'll go to the yellow LED level
that I have in my difficulty rating at
the beginning of each video when we talk
about stuff like wireless communication
serial connects between the Arduino and
various integrated circuits and things
like that it should be very educational
and I'm really looking forward to moving
into some more difficult material as
always please let me know if you have
any questions or comments about these
videos or suggestions or anything like
that I look forward to hearing from you
guys and I'll see you soon 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 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