Events
Leonardo
- Wednesday @ 7pm (ish)
- Great speakers on interesting things
- Here's this months
- If you want to go, please email p(at)scaruffi(dot)com and let him know you want to, asap the rsvp
Review
From Tuesday's Code
Connecting Components
A switch with a pull-up resistor

This circuit will get a digitalRead(switchPin) of 1 until the switch is depressed, then it will read 0.


¿Por Que? Because not using one can lead to "open grounds," which can cause spurious voltages to sometimes creep into the pins you're testing for voltage values
A switch with a pull-down resistor

This circuit will get a digitalRead(switchPin) of 0 until the switch is depressed, then it will read 1.


¿Por Que? Same issue as pull-up resistors
A potentiometer

This circuit will get an analogRead(potPin) with a range from 0 to around 1023. 0 when the potentiometer is turned closest to ground.


Interestingly, the potentiometer, since it's hooked to ground, will act as a "voltage divider," (which it would not do if you didn't hook up the ground). This gives reading between 0 and 1023 with the Arduino no matter what Ohm value you use for the potentiometer.
A Photoresistor
Sensors
Three basic Kinds
- Those that return voltages (0 to some Voltage value)
- Those that return serial data (1's and 0's)
- Those that return 1 or 0 (on or off)
PIR Sensor
- Super simple 1 or 0 result
- Detects changes in InfraRed. When the sensors detects a change in the InfraRed blurry image of the room it changes from 0 to 1 (no voltage to +5 volts)
- A WikiPedia explanation
// Read PIR sensor
// Vars
int PIRPin = 12;
void setup() {
Serial.begin(9600);
pinMode(PIRPin, INPUT);
}
void loop() {
Serial.println(digitalRead(PIRPin));
}
Parallax Ping Sensor
- Returns a digital pulse that has to be timed in milliseconds, which accurately correspond to distance
Download ultrasound_sensor.txt file
/* Ping))) Sensor
From: http://arduino.cc/en/Tutorial/Ping?from=Tutorial.UltrasoundSensor
This sketch reads a PING))) ultrasonic rangefinder and returns the
distance to the closest object in range. To do this, it sends a pulse
to the sensor to initiate a reading, then listens for a pulse
to return. The length of the returning pulse is proportional to
the distance of the object from the sensor.
The circuit:
* +V connection of the PING))) attached to +5V
* GND connection of the PING))) attached to ground
* SIG connection of the PING))) attached to digital pin 7
http://www.arduino.cc/en/Tutorial/Ping
created 3 Nov 2008
by David A. Mellis
modified 30 Jun 2009
by Tom Igoe
*/
// this constant won't change. It's the pin number
// of the sensor's output:
const int pingPin = 12;
void setup() {
// initialize serial communication:
Serial.begin(9600);
}
void loop()
{
// establish variables for duration of the ping,
// and the distance result in inches and centimeters:
long duration, inches, cm;
// The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
pinMode(pingPin, OUTPUT);
digitalWrite(pingPin, LOW);
delayMicroseconds(2);
digitalWrite(pingPin, HIGH);
delayMicroseconds(5);
digitalWrite(pingPin, LOW);
// The same pin is used to read the signal from the PING))): a HIGH
// pulse whose duration is the time (in microseconds) from the sending
// of the ping to the reception of its echo off of an object.
pinMode(pingPin, INPUT);
duration = pulseIn(pingPin, HIGH);
// convert the time into a distance
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm");
Serial.println();
delay(100);
}
long microsecondsToInches(long microseconds)
{
// According to Parallax's datasheet for the PING))), there are
// 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
// second). This gives the distance travelled by the ping, outbound
// and return, so we divide by 2 to get the distance of the obstacle.
// See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds)
{
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the
// object we take half of the distance travelled.
return microseconds / 29 / 2;
}
