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Slide 1
Scratch for ArduinoLesson 3 – Analog Input
Potentiometers, Variables, and Etch-a-Sketch*
Etch-a-Sketch may be omitted due to safety concerns.
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Slide 2
Analog Input
● Today we will extend the ongoing LED project by introducing an analog input device
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Slide 3
Graphical Dimmer Switch
● Last week some of you may have completed the Graphical Slider control
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Slide 4
● Today we will be using a Potentiometer as a variable resistor, or Rheostat, to recreate the effect with a physical switch...
Physical Dimmer Switch
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Slide 5
● What is electrical resistance?
Resistors & Variable Resistors
a measure of the difficulty to pass an electric current through a circuit element
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Slide 6
● Fixed Resistors have fixed resistance
Resistors & Variable Resistors
● Variable Resistors have variable resistance
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Slide 7
● Inside there’s a fixed resistor and a wiper that points between the minimum and maximum terminals of the resistor
Variable Resistors
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Slide 8
● Let’s use a multimeter to measure the minimum and maximum resistance of the wiper terminal
Variable Resistors
? ohms
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Slide 9
● Resistance causes voltage to drop, so the potentiometer also behaves as a Voltage Divider
Variable Resistors
5 V0 V
0 V
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Slide 10
● Resistance causes voltage to drop, so the potentiometer also behaves as a Voltage Divider
Variable Resistors
5 V0 V
5 V
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Slide 11
● Resistance causes voltage to drop, so the potentiometer also behaves as a Voltage Divider
Variable Resistors
5 V0 V
2.5 V
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Slide 12
● Resistance causes voltage to drop, so the potentiometer also behaves as a Voltage Divider
Variable Resistors
5 V0 V
1 V
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Slide 13
● Unlike the digital pins which read either 0 or 1, analog inputs can read a range of values.
Analog vs. Digital Input
5 V0 V
?
Let’s find out what that input range is...
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Slide 14
Let’s Get Hands-On
(the exciting part…?)
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Slide 15
Connect to Arduino
This end to computer
This end to Arduino
Some of the LED on the Arduino should light up after connection
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Slide 16
Start up mBlock
● Don’t forget mLink● Go to https://ide.mblock.cc to start mBlock● File → New
Get rid of this guy
Add this one instead
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Slide 17
Connect with Arduino
● Switch to “Live” mode and “Connect”
● Select a COM port[x] “Show all connectable devices”
● If appears, click on
it followed by and
“Updates”
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Slide 18
Review Breadboard
Use long strips to create lots of pinholes for GND & 5v
Useful when connecting multiple devices
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Slide 19
Potentiometer Circuit
+-
+-
5 V
-
GND5 VA0 port will read the Potentiometer wiper.
GND & 5v connected through long strips.
Leave room for the LED circuit!
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Slide 20
Exercise 3a
Read Analog Input
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Slide 21
Read Analog Input
Need to do something with the value….
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Slide 22
Read Analog Input
Create a new variable.
Keep reading the Analog Input pin A0 in a loop.Set the variable to the value.See Monitor
on the Stage
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Slide 23
Challenges● Note in your Student Handout the min/max values for
the A0 readings for the Potentiometer’s Wiper
● Write a program that:
1) checks if Potentiometer wiper is closer to GND or closer to 5V
2) if closer to GND Panda says “GND”
else
Panda says “5V”
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Slide 24
Condition on Analog Input
Add the Panda portion & Test it out!
Can you add conditions for 4 different outcomes?
The “if – then” and “if – then - else”conditional constructsare very importantin programming.
They allow you to change the behavior of your program based on input or state.
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Slide 25
Light Control
● Back to our dimmer effect...
● Let’s combine our LED and Potentiometer circuits to re-create this effect.
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Slide 26
Challenges
● Make a Physical Dimmer Switch:
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Slide 27
Dimmer Switch Circuit
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Slide 28
Challenges
● In your Handout, note the math required to convertbetween 0-1023 (input) and 0-255 (output)
● Then program it in mblockHint: look at the map block under Data
0-1023 ? 0-255
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Slide 29
Exercise 3b
Mapping Input to Output
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Slide 30
We should now have two variables.
One to read Potentiometer from A0.
Second to store the mapped output PWM (0-255).
Variables
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Slide 31
Dimmer Program
1) Read and store A0
2) Map and store PWM output3)Output PWM to
the LED pin
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Slide 32
Challenges
● Try to upload the program to the Arduino for a smoother effect. Just change the mode, and the start event to when Arduino starts up.
● Change the program so that the Potentiometer controls how fast the LED blinks, instead of its brightness level.
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Slide 33
Exercise 3c
Move, Panda, Move!!!
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Slide 34
Move, Panda, Move!● Make Potentiometer control Panda’s X-axis position.
1-D Joystick
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Slide 35
Move, Panda, Move!● Find Pand X-axis min and max (move it around)
● Map A0 to Panda’s X-limits and store in a variable (for all sprites).
● Tell Panda to set its position to that saved value.
1-D Joystick
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Slide 36
Move, Panda, Move!
1-D Joystick
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Slide 37
Challenges
● Make Panda point towards the new X ● Make Panda look like it’s walking by changing
costumes– And make Panda only walk when it’s moving…
● Add a second Potentiometer to control Y.Like an Etch-a-Sketch!
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Slide 38
Extra Challenges
● Use multiple LEDs to create a Metering Effect. The bigger the reading, the more LEDs are lit.
You can start with 3 LEDs, e.g.:
if (A0 < 330) turn off everythingelse if (330 < A0 < 660) turn on 1else if (660 < A0 < 990) turn on 2else turn on 3
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Slide 39
Copyright
● Created by A Posteriori LLP● Visit http://aposteriori.com.sg/ for more
tips and tutorials● This work is licensed under a Creative
Commons Attribution-ShareAlike 4.0 International License.