This week on Let’s Make It we have an Arduino control a servo like you find in model airplanes and cars.  In the process of showing you how to control a servo we also introduce the concept of Pulse Width Modulation (PWM) and Pulse Position Modulation (PPM).

Downloads

Servo Sweep

For the code for the Servo Sweep in the Arduino software go to File -> Examples -> Servo -> Sweep.

Set Servo Position

/*############### SET SERVO POSITION BASED ON SERIAL INPUT #########################
       This code will take input from the Serial port in the form of a number.
       
       It takes this number and positions a servo between 0 and 180 degrees.
       
       To know when the number actually ends, a non numeric character must follow
       the number.  Typically the serial input would not be used, it is just for this 
       example.

 
   From: Mike Myers (http://mikemyers.me)  @netnutmike
       Let's Make It Episode 12 (http://tech-zen.tv/index.php/shows/let-s-make-it/episodes/59-sensor-fun-with-arduino-1-massive-failure-but-4-successes-let-s-make-it-episode-6)
       
       http://tech-zen.tv
       
       For the sample code, show notes, contact information and many more 
       videos, visit the show page at http://tech-zen.tv/letsmakeit

       Please subscribe to our YouTube channel or our netcasts at any of 
       your favorite netcast / podcast outlets.

       We normally record Let's Make It live on Tuesday evenings around 
       7pm eastern. You can watch it live by going to tech-zen.tv and clicking 
       the live link at the top of the page.

       We also have a community setup for our viewers and listeners. You can 
       join the community by going to community.tech-zen.tv.

       We love input on what you would like to know or if you have an idea for 
       a new Let's Make it episode, you can contact us via email or phone at 
       the show information page.
################################################################################*/

#include <Servo.h> 
 
Servo myservo;          // Create servo object to control a servo 
 
char readstr[4];        // Character Array to store the serial input
int cstrpos = 0;        // Variable to store the current input array position
long val = 0;           // variable to store the value from the input 
 
int maxValue = 175;
 
void setup() 
{ 
  Serial.begin(9600);   // Startup the Serial Interface
  myservo.attach(9);    // Attaches the servo on pin 9 to the servo object 
} 
 
void loop() 
{ 
  char ch;              //A Place to Store the character we just read
  
  if (Serial.available())      // is there anything to be read from serial port?
  {
    ch = Serial.read();        // read a single character
    
    // print out to serial port the character we received (similar to an echo)
    Serial.print(ch);
    
    if (ch >= '0' && ch <= '9')    // Number so store it in the input array
    {
      readstr[cstrpos] = ch;      // Add the read character to the array of read numbers
      ++cstrpos;                  // Increase the position in the array
    }
    else                          // not a number so lets set the position of the servo
    {
     readstr[cstrpos] = '\0';     // Add a null to the end of the string array to terminate the string
     val = atol(readstr);         // Convert the string to a long int
 
     if (val > maxValue) {
       val = 175;
     }
     
     cstrpos = 0;                 // Reset the array position back to the beginning so the next input starts a new input
     
     //Print to the serial port what we are going to do
     Serial.print("Servo set to: ");
     Serial.println(val);
     Serial.println("");
    }
  } 
  
  // The servo needs constant feed of values so we constantly output the PWM value
  myservo.write(val);            // Set the PWM value to send to the servo
  delay(15);                     // Just a little delay
    
}