Transcript Electric Circuits

Working with Arduino:
Lesson #2: Variable, Photo, and Force
Sensitive Resistors
EGN1007
Learning Goals
Learning Goals: The student will be able to:
1. Build a complete circuit using the Arduino microprocessor
2. Identify important electrical components in a circuit and explain their
use
3. Identify and apply specific elements in “C” code used to run a
program in conjunction with how a circuit is built
Variable resistors
Along with the digital pins on the Arduino, the board also
has 6 analog pins which can be used. These inputs take
a voltage between 0 and 5 volts and convert it to a digital
number 0 to 1024. A device which uses these inputs is
called a POTENTIOMETER or variable resistor.
When a voltage is applied to the outer
pins, the middle pin will read some
value between 0-5 volts depending on
the angle of the position.
The schematic symbol is that of a
regular resistor with an arrow either
through it or perpendicular to it.
Let’s Begin
1. Place the potentiometer on D5-D7.
2. Run a red wire from the 5V on the
Arduino to E5. This will supply the
Pot with 5V.
3. Run a wire from Analog 0 to E6.
4. Place the LED on J5 and J6 with
the longer lead(+) of the LED in J5.
5. Place a resistor on I6and I16.
Notice that both the resistor and
LED share row 5
6. Run a red wire from Digital 13 port
on Arduino to I5.
7. Run a black wire from H16 to the
ground(GND).
8. Run a black wire from E7 to G16.
Programming our sketch
Let’s define 3 variables as integers.
These will tell us which ports our
LED and POT are in
This is a variable that we will use which can store a value coming from the POT.
Programming our sketch
Just like before we need to set our LED as an output.
Programming our sketch
The sensorValue is determined by the actual READING on the POT
The only difference this time is that the delay is caused by the
READING on the POT which is referenced by the sensor’s value.
Your turn!
Using what you have learned in this lesson
AND the last lesson. Write a short program
that uses the POT to control the brightness of
the LED. HINT: Do not allow it to blink!
Write your code on the lesson worksheet and
explain your code.
PhotoResistors
This type of resistor produces a variable
resistance based on the amount of incident
light.
The schematic symbol shows light in
the form of arrows coming down and
striking the resistor symbol.
To be used correctly is MUST be in a VOLTAGE DIVIDER.
Voltage Divider
A voltage divider is a simple circuit consisting of two resistors that has
the useful property of changing a higher voltage (Vin) into a lower
one (Vout). It does this by dividing the input voltage by a ratio
determined by the values of two resistors (R1 and R2):
So lets say that R1 is the photocell and R2 was a regular resistor. Ss the
resistance of the photocell changes as a function of light intensity, the current
flowing would increase and decrease. This will cause a voltage that
CHANGES and changes in voltage is what Arduino can sense and
understand.
Let’s Begin
1. Place the photoresistor on J20 &
21.
2. Run a red wire from the 5V on the
Arduino to J20. This will supply the
PR with 5V.
3. Place the 10K resistor (brownblack-orange) on I21 and I30.
4. Run a wire from Analog 0 to H21
5. Place the LED on J5 and J6 with
the longer lead(+) of the LED in J5.
6. Place a 560W resistor on I6 and
I16. Notice that both the .resistor
and LED share row 5
7. Run a red wire from Digital port 9
on Arduino to I5.
8. Run a black wire from J16 to the
ground(GND).
9. Run a black wire from H30 to H16.
Programming the sketch
These will tell us which ports our
LED and PR are in.
Programming our sketch
Just like before we need to set our LED as an output.
Programming the sketch - map
map(value, fromLow, fromHigh, toLow, toHigh)
Re-maps a number from one range to another.
That is, a value of fromLow would get mapped
to toLow, a value of fromHigh to toHigh,
values in-between to values in-between, etc.
Why do we have to do this? The LED understands the range 0 to 255 and
the photoresistor will export values between 0 and 900
Programming the sketch - constrain
constrain(x, a, b)
Constrains a number to be within a range.
Example
sensVal = constrain(sensVal, 10, 150);
// limits range of sensor values to between 10
and 150
Why are we doing this?
(I told I was going to explain this later)
Remember that the Arduino is a digital
machine. It can only deal with analog via
special tricks.
analogWrite (pin, value) - turns the pin ON
and OFF very quickly which makes it act like
an analog signal. This value is between 0 (0
volts) and 255(5 volts)
Why are we doing this?
(I told I was going to explain this later)
Remember that the Arduino is a digital
machine. It can only deal with analog via
special tricks.
analogREAD (pin, value) - This allows you to
read the their voltage which outputs a value
between 0 (0 volts) and 1024 (5 volts)
The bottom line
When you READ a range from 0-1025 you
must MAP and CONSTRAIN that range if you
want to WRITE (0-255)it to a different device.
Therefore we READ the value from the PR. We
then map and constrain it so that we can
WRITE that value to the LED. The written
value is then outputted as brightness in the
LED.
Programming our sketch
We first create a variable to READ the value of the PR
We then RE-MAP the ranges that the PR can produce to those same
values we used to control the brightness of the LED. We also
constrain these values to this range.
Lastly, we send the value (voltage) to the LED based on the
LIGHTLEVEL of the PR.
Place your hand or finger on the PR to dim the LED.
Challenge – Night Light
Instead of lowering the LED brightness when
the light level on the PR is LOW, can you
figure out a way to turn the LED ON when the
value across the PR is LOW and OFF?
Hint: Use an “IF-ELSE” statement and other ideas from lesson 1
like math functions (+,-,*,/,<,>).
Write out what you WANT to do in WORDS first (psuedo-code) as
this may help you determine how this is to be done.
YOU CAN DO THIS! And, YES……turn off the lights to test.