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172 Making Things Move

3. Connect the red wire to 5V power, the black wire to ground, and the yellow
wire to digital pin 2 on the Arduino. Sometimes this third wire is green or
orange, but it will always be different from the red (power) and black (ground)
wires.

4. Connect one leg of the photocell directly to power.

5. Connect the other leg to a row on the breadboard of your choice. Then
connect this row to ground through the resistor. Also connect this row to
analog pin 0 on the Arduino. Your circuit should now look like Figure 6-33.

NOTE We need to use the analog pins with a photocell because it’s not
just an on-off type of input like the switches we’ve used until now. The
photocell will actually indicate a value between 0 and 1023 (as will any
analog sensor), depending on how much light is hitting it.

6. Open a new sketch in Arduino and type the following code. Then verify and
upload the code to the Arduino.

/*
Servo control from an analog input using the Arduino Servo library

Created June 2010
By Stina Marie Hasse Jorgensen and Dustyn Roberts
Adapted from code at http://itp.nyu.edu/physcomp/Labs/Servo
*/
#include <Servo.h> // include the servo library

Servo servoMotor; // creates an instance of the servo object
// to control a servo
int analogPin = 0; // the analog pin that the sensor is on
int servoPin = 2; // the digital pin for the yellow servo
// motor wire
int analogValue = 0; // the value returned from the photocell

void setup()
{
servoMotor.attach(servoPin); // attaches the servo on Arduino pin
// 2 to the servo object
}