Transcript Lesson 3 - Analog Inputs - Columbia University | IGERT

Digital & Analog Inputs
Review
• Fundamental parts of an Arduino
program are …
• Setting output types using pinMode.
• Declaring variables
• Can write a digital signal (0/1) to a pin
using digitalWrite.
• Can read a digital signal (0/1) from a pin
using digitalRead.
– Must have a variable to store the value
IF, IF-ELSE, and IF-ELSE-IF
if (someCondition)
{
// do stuff if the condition is true
}
if (someCondition)
{
// do stuff if the condition is true
}
else
{
// do stuff if the condition is false
}
if (someCondition)
{
// do stuff if the condition is true
}
else if (anotherCondition)
{
// do stuff only if the first condition is false
// and the second condition is true
}
Your turn
• Challenges: Complete in order
1. Push the button and have it display an LED pattern
•
Fireworks!
2. Push the button and have it turn on alternate LEDs
•
•
3.
Button HIGH – Yellow
Button LOW – Red
Push the button twice to turn on LED
• Need a COUNTER -- if you get to this stage, ask one of us for
help 
ANALOG INPUTS
Analog Signals
• What is an analog signal and how does it differ
from a digital signal?
0
1
1
0
1
1
1
0
Analog Signals & Arduinos
• The Arduino can read an analog signal on one of
the analog input pins.
– analogRead
• The signal that can be read must be between 0
and 5 V.
• The Arduino converts the signal to a number
between 0 and 1023.
• How many values are there for a digital signal?
How many values are there for an analog signal
on the Arduino?
Program Time!
• We’re going to write a program that will turn
on the Arduino’s LED when “threshold” value
is reached.
How:
• Use a Voltage
Divider to change the
voltage on the analog
input pin.
• Use the Arduino to
detect when the
voltage has reached a
certain level.
• Turn on the LED!
Analog
Input
Potentiometer
Analog Signal Detector
• Step 1 – Declare Variables:
int inputPin = 0;
// select the input pin for the potentiometer
// ( can be 0 through 5).
int ledPin = 13;
// select the pin for the Arduino’s LED
int inputValue = 0; // variable to store the value coming from
// the voltage divider.
• Step 2 – Setup:
void setup()
{
pinMode(ledPin, OUTPUT);
//Declare the LED pin as an
//output.
}
• We do NOT have to declare the analog pin as an input. Why?
Analog Signal Detector
• Step 3 – The Loop:
void loop()
{
inputValue = analogRead(inputPin);
if(inputValue > 511)
{
digitalWrite(ledPin, HIGH);
}
else
{
digitalWrite(ledPin, LOW);
}
}
// Read the analog
//input, what are
// the possible values.
// Check our threshold.
// Turn on the LED.
// Turn off the LED.
Your turn
• Challenges: Complete in order
1. Design a program to make the LED flash at a
speed dependent on the value on the analog
input pin.
2. Turn on a number of LEDs that is proportional to
the analog input value.