Learning to Program the Arduino

Listing 4. Fade an LED On/Off Using a Flex Sensor

/* Flex sensor + LED
/* Analog Input
* Demonstrates analog input by reading an analog sensor
* on analog pin 0 and turning on and off a light emitting
* diode (LED) connected to digital pin 13.
* The amount of time the LED will be on and off depends
* on the value obtained by analogREAD().
* Created by David Cuartielles
* Modified 16 Jun 2009
* By Tom Igoe
* http://arduino.cc/en/Tutorial/AnalogInput
* Modified 16 July, 2011
* By Amit Saha
* Current code was tested with a Flex sensor
*/
int sensorPin = 0; /*Flex sensor pin */
int ledPin = 13; /* LED pin*/

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {

  int loop=1;
  float sensorValues=0.0,delaytime;
  for(loop=1;loop <=10 ;loop++)
  {
     sensorValues = sensorValues + analogRead(sensorPin);
  }

  //Use the average as a delay value
  delaytime = sensorValues/10;

  digitalWrite(ledPin, HIGH);
  delay(delaytime);
  digitalWrite(ledPin, LOW);

delay(delaytime);
}

The flex sensor has two pins: one end should be connected to the +5V input, and the other pin should be connected to the analog pin 0 and farther on to the ground via a 10 kOhm resistor.

Serial Communication

All the sketches so far have made use of the Arduino library calls to read and write to the Arduino pins. You haven't directly made use of the serial communication between the host computer and the Arduino board. First, I'll describe how to write a basic client/server style program.

The "server" program is a sketch that lives on the Arduino board waiting for serial data to be available (an integer in this case) and sends back the number by adding 1 to it to the "client".

Listing 5. Example of a Server Sketch

/* Serial communication demo: +1*/

/* Server program
Amit Saha*/


int number;

void setup()
{
  // Open the serial connection, 9600 baud
  Serial.begin(9600);
 }

void loop()
{
  // Get the data "packet"
  // Wait for some data to arrive
  if (Serial.available()>1) {
      //operation=Serial.read();
      number=Serial.read();

      Serial.println(number + 1);
    }

}

The client side of the program is written in Processing using its serial library (Listing 6).

Listing 6. Example of a Serial Client Sketch

/*Client for Serial communication*/
/* Amit Saha */

import processing.serial.*;

Serial myPort; // The serial port

// initial variables:
int i = 1; // counter
char inData;

void setup () {

size(400, 350); // window size

// List all the available serial ports
println(Serial.list());

// Pick up the first port, since I usually have
// just the Arduino connected.
// Make sure the correct port is selected here.
myPort = new Serial(this, Serial.list()[0], 9600);
myPort.clear();

// set initial background:

background(255); }

void draw () {

  myPort.write(4);
  //myPort.write(5);

  if (myPort.available() > 0) {
    inData = (char)myPort.read(); // Typecast it to the corresponding
                                  // character for the
                                  // ASCII value
    serialEvent();
   }

}

void serialEvent () {
  System.out.println(inData);
}

To run the client, download the processing IDE and create a new sketch with the code as shown in Listing 5. Run this code after you have uploaded the server sketch (Listing 5) to the Arduino.

Controlling a Servo

Now, let's make things move with your Arduino code. For this example, let's control the movement of a servo—that is, start and stop the servo and control its speed and rotation. Three wires protrude out of the servo: control (white/yellow), power (red) and ground (black/brown). First, set up the circuit such that the the control wire is connected to the Arduino's digital pin 2, the red wire is connected to the Arduino's 5V input and the black wire to the ground. Now, upload the sketch (Listing 7) to your Arduino. You also optionally may connect an LED to the digital pin 13 (in the same way you connected a single LED earlier), which will turn on or off depending on whether the servo is rotating.