Tutorial 04 for Arduino: Analog Inputs Video Lecture | Arduino Programming: Step by Step (to become an Expert) - Electronics and Communication Engineering (ECE)

hey everyone
Jeremy Blum here with our do editorial
number four we're on a roll here today
we're going to be talking about analog
inputs to the Arduino I'm going to talk
about setting a reference level for the
analog voltage taking an analog voltage
in from either a pre-made sensor or
building one yourself using a variable
resistor and a voltage divider which is
something we talked about last week and
then we'll talk about mapping those
values to different values in the
Arduino programming language using it to
control LED brightness which is an
analog output and a few other
applications so let's get started let's
talk a little bit about how analog
inputs are set up on the Arduino boards
here I have the uno the mega 2560 and
the nano boards all of these allow for
analog input options and on all our
Lino's there is a 10 bit analog digital
converter that allows you to convert
from ground up to the input voltage of
the Arduino usually 5 volts to a value
from 0 to 1023 that means you have a
thousand 24 bits of resolution or two to
the 10th power
hence why it's called 10 bit resolution
if you want to learn a little bit more
about how analog digital converters work
please watch my tech bits episode on
analog and digital signals you can set
the reference voltage that you use for
the analog inputs on all these Arduino
boards by default it's set to 5 volts or
3.3 volts on 3.3 volt on are we no
boards but here we'll just be walking
working with the default 5 volt boards
you can also set it to an internal 1.1
volt reference although that's not
available on the mega and on the mega
you can use different command set it to
one point one volts or two point five
six volts as a reference you can also
select your own voltage reference by
setting it to an external value which
you input into an analog pin on the
Arduino here we can see the analog
reference pin I was talking about you
might want to consider using an external
analog reference if you're only using
sensors that go from 0 to 3.3 volts on a
5 volt Arduino the reason for this is
that the values from 3.3 volts up to 5
volts if you use the default 5 volt
reference will basically be excluded and
you'll be getting less resolution than
you potentially could use an external
voltage reference allows you to
eliminate that problem down here on the
bottom we can see
the analog inputs a zero through a five
there are six inputs available on
Arduino Uno
if we look now at the mega the mega has
many more analog inputs available all
these right here analog inputs 0 through
15
so there's 16 analog inputs available on
the mega and if we look at the Nano
board we can see that there are actually
8 analog inputs available on here for
our first sensor let's use a simple
photo resistor photo resistors simply
decrease their resistance as the ambient
light in the room increases as I
decrease light in the room the
resistance will increase so if we hook
this up in a voltage divider circuit
with a fixed resistor we can essentially
feed into the Arduino a voltage that
varies with light in the room let's hook
that up using this schematic here's our
assembled circuit just like in the
schematic we have a photo resistor
connected between 5 volts and a 10k
resistor the 10k resistor then goes to
ground and at the junction between two
of them we take a wire out and go to
analog input 0 on the Arduino this is
just like our voltage divider setup that
we worked on in the last episode
now let's program this to show us the
values from the photo resistor as we
change light in the room note that you
can change the position of the photo
resistor and the fixed resistor and the
values in the computer will inverse
that's really a quick program that will
show us the value of this sensor so
first we'll need to define our input
pins we'll call it sin spin that's going
to be equal to analog input on pin 0 now
we always want to do our setup function
and in here we don't need to define as
an input pin because it's sent to that
as default we can define the analog
reference as default that's because
we're going from 0 to 5 volts but again
this line isn't necessary it will do
this by default but I'll just put in
here for complete coverage and we want
to print this to this screen so let's
set up our serial connection like we did
last time and the 9600 just means the
speed at which we're communicating with
the computer 9600 baud is a pretty
common value that you use alright and in
our loop all we're going to do is read
the sensor and then print it to the
screen so serial dot print line just
like last time analog read and the
sensor of pin sense pin make sure we
close our parentheses and we don't want
to spit out values constantly so we'll
just put a delay in there of 1/2 second
that should be good all right
let's see how this works out so we can
see that ambient light we're getting a
value of about 950 and as I put my hand
over the sensor we can see that drops
down if I cover it completely we go down
to about 750 ish 770 ok great that's
only giving us a range of 200 out of a
potential range of a thousand 24 why is
that well it's partially because of the
resistors that we've chosen and the
inherent fact that you're going to lose
some values by using a voltage divider
which is fine we don't need the full
1024 resolution you can overcome this by
setting up an op-amp and doing a few
other things but it's not really that
important to us if we want we can try to
change the resistor to a 1k resistor and
see how that changes it now we've got a
1k resistor in the circuit instead of a
10k resistor and we can say let's change
the values now ambient light is closer
to around 570 and if I put my hand over
it drops down to it about 200 so that
range is a little bit better not by much
and you can keep messing with the
resistor values until you get a value
where you where you're happy but in
reality this amount of range is fine for
what we want to do we just saw that a
value of around 9
ambient lighting in the room so let's
make a simple nightlight now if the
value goes below 800 we'll turn on an
LED that will illuminate the room so all
I've done here is add an LED to our
circuit with our 150 ohm resistor same
as we used last time and I've hooked it
into pin 9 on the Arduino so let's go
program that all right the first thing
we'll have to do is to add our LED pin
here and it's going to be pin 9 next up
we have to set that pin as an output
because if it hit the defaults to an
input so let's make the LED in output
and we can get rid of the serial
communication we're not going to use
that anymore okay
down in our loop let's start by getting
the value from the sensor and saving it
to a variable so we'll make a new
variable called Val pretty standard name
do an analog read a sense pin we don't
need this one
we have Nydia these anymore right and
then if the value is less than 800 we'll
do something so I'll use an if statement
which checks the value so if the value
is less than 800 we will do a digital
write to the LED pin and try it on
otherwise if it's a greater than 800
let's make sure we turn it off digital
write LED pin low which will turn it off
and that's it so let's CSS works
okay great we put our hand over and the
LED turns on just like we wanted to it
gets too dark in the room we'll have a
nightlight now now you don't have to be
afraid of monsters in your closet now
let's make our nightlight a little bit
more adaptive we'll have it change
brightness based on the brightness in
the room as the room gets darker the LED
will get brighter to illuminate the room
better we're going to do a few things to
do this first off we need to map our
value so there's a function in Arduino
called the map and map takes in the
original value Val in this case and
values to map it to so the reason we do
this is because our value for an analog
input can range from anywhere from zero
to a thousand twenty three where as
analog output what we'll be using to
change the brightness of the LED is only
zero to 255 additionally we want an
inverse relationship as the value from
the light sensor increases we want the
value on the LED to decrease and
vice-versa so the map function will
allow us to do that if val is the
function we want to map and let's say
we'll set 750 as the minimum and 900 as
the maximum and that will map to 255 and
zero
and we'll set that new value equal to
LED level so precisely what this is
doing is it's taking in valve from the
sense pin the value of 750 gets
converted to 255 the value of 900 gets
converted to zero anything in between
scales proportionally so as the value
increases from 750 to 900 this value
will decrease our LED level will
decrease from 255 down to zero which we
can then feed into our LED to change its
brightness we want to do one more thing
now it's to check for values outside of
750 or 900 if it's less than 750 or
greater than 900 we want to set it equal
to those values so that we're not
dealing with anything greater than or
greater than 255 or less than zero
across the analog output won't know how
to handle that correctly so we'll use
one more function and we'll reset our
Val first using constrain
constrain is another Arduino function
that takes in a value and then sets
minimum and maximum values so we'll set
it to the same value 750 900 now what
this does is takes the value from our
sense pin if it's less than 750 it
resets it to 750 if it's greater than
900 it sets it up to 900 now we only
have to worry about values between these
two which means these values will always
be between 255 and 0 just as we want
them to now we can get rid of this and
just use analogue right to set the
brightness of the LED directly analog
right LED pin and will now set it to LED
level awesome let's see how that works
ok so the LED starts off like we expect
it to and as I move my hand closer we
see the LED incrementally gets brighter
until it's at full brightness when I
have the sensor in complete darkness and
it scales back just the same way perfect
we now have an adaptable nightlight
naturally photo resistors aren't the
only kind of variable resistors that you
can use in a circuit like this here I
have a thermistor which varies its
resistance with temperature as I hold on
to it you can see that the value drops
from 460 down to that 440 so this is
actually working the opposite direction
of the photo resistor if we wanted to
increment the values in the same
direction as the other one we could swap
it with the resistor another thing to
experiment with is using different
resistor values if you look at the
voltage divider equation that I showed
you in the last episode you'll see how
setting this resistor will affect the
range that you've got the analog
readings on and then of course you can
also use op amps to scale the readings
up so you get a better resolution but we
won't cover that in this episode of
course you don't always actually have to
build your own sensor you can often buy
preassembled sensors that are designed
to output at a certain voltage so you
don't have to worry about scaling them
or adding a voltage divider circuit or
anything like that this is an example of
one this is an infrared distance sensor
it uses an infrared emitter and receiver
to bounce infrared light off an object
and detect the distance to it all
sensors that come like this will usually
have three wires a voltage wire
wire and a sense wire the red wire we
give it 5 volts ground gets next the
ground of course and then the yellow
wire returns a value between 0 and 5
volts that we can feed into the analog
digital converter and the hard we know
and use it to measure a distance value
you'll often notice that these kinds of
sensors will give you a broader range
because they've already designed it to
operate on the whole 0 to 5 volt range
you can also buy these centers in 3.3
volt iterations and other voltage
versions so if we look at the screen now
as I move my hand closer and closer you
can see that the value slowly increases
from about 50 all the way up to about
600 something let's wrap up today's
tutorial with our first little project
this project will combine the infrared
distance sensor and the photodiode that
we used today to make an emergency
lighting system in the event that a room
is dark detected by the photodiode and
movement is detected by looking at
values from the infrared distance sensor
we'll turn on our emergency lighting
system in this case an LED although you
can easily hook this up through a relay
to control a more powerful bulb a lot of
the code we'll be using to make this
system work is very similar to what we
had before there's only a few
modifications that we need to make to
put everything in place the first thing
is we're now using two analog inputs and
I'll again put 0 and analog input one
zero is connected to the distance tech
door in this case a motion detector as
we're using it and analog input 1 is
connected to the photodiode which I'm
calling light pin we still have an LED
connected to pin 9 next up we're going
to need to make to various to keep track
of the distance what we'll do is every
time through the loop will keep truck
we'll look at what the distance is from
the infrared distance sensor and compare
it to what the distance was last time if
it changes significantly from the
previous detected value we can assume
that something has passed in front of
the infrared distance detector and
assume that movement has occurred so
we'll use these two variables to track
that in the loop our threshold defined
by interest at about 200 this is
basically the value 4 which is looking
for deviation amount between the last
distance and the current distance you
can fine-tune this to make system as
sensitive or as insensitive as you want
I found that 200 works pretty well setup
is the same we just have to configure
LED pin as an output everything else is
defaulted
and here's our loop so first off we're
going to read our light value and from
the photodiode using analog read just
like we did before and we'll read in our
current distance from analog read
emotion pin note that here I have to
define light valance into because this
is the first time I'm using it current
distance I've already defined as an int
up here so I don't need to use the
integer term again the next thing we're
going to do is look if everything meets
our conditions so this if statement will
check if the threshold has been exceeded
and if the light value is less than
value of 800 so how are we doing that
let's break it down there's two parts
here the part in this set of parentheses
and the part checking for the light
value those two parts are separated by
double ampersand which is a logic and
that means if both the contents of this
parentheses are true and the end this is
true right here then we'll execute the
if statement which turns the LED on for
one second if we look more specifically
into this part of the if statement we
can see that we're checking for our
thresholds these double pipes indicate a
logic or so either this or this has to
be true for this entire part of the if
statement to be validated as true the
first part before the double pipes says
current distance is greater than the
last distance plus the threshold so if
our threshold is 200 and our previous
distance was 300 then if current
distance is more than 500 then this will
evaluate to true alternatively it'll
evaluate to true if the last distance
was something like 500 and then that
minus threshold of 200 is 300 so if
current distance was less than 300 that
would also indicate a significant change
and that would also evaluate this to
true so if all that's if one of these is
true and then this is true also
then we'll digital write the LED to high
and turning it on leave it on for one
second to make sure people have enough
time to find their way it'll stay on if
it continues to detect movement
otherwise we'll turn the LED back off
and then the last thing we have to do is
set last distance equal to current
distance so at the next time through the
loop we can compare the distance that we
use this time to the loop with the new
distance so if I just put my finger over
the photodiode or I just make some
motion they only do you want to turn on
but if
room is both dark and motion is detected
the LED will turn on for a second and
help anyone who's roaming through the
dark find where they need to go thanks
for watching this episode of my Arduino
tutorial series if you have any
questions or comments or if you want to
watch the other videos in this series
you can do so on my youtube channel so I
got 14 on my blog Jeremy Blum comm or
over at the element 14 Arduino group I
hope you guys enjoy this and I'll see
you guys next week 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 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