Servo motors

Figure 1: Standard servo

A standard servo rotates over 180 and is useful for controlling actuators such as valves or automatic door openers. Please see the notes for more information.

Firstly, the Particle development environment simplifies things a little in comparison to Arduino because the servo object is built-in. With an Arduino you need to explicitly include a servo library. On the hardware side though, a standard servo requires 5V to operate and the Argon is a 3.3V device. If your Argon is connected to a computer or a power outlet via USB, then you can take 5V from the VBUS pin to power the servo. Another complication is that controlling a servo requires pulse-width modulation (PWM) which is only available on some of the Argon's digital pins. Figure 2 shows you how to connect up your servo using VBUS.

Figure 2: Breadboard layout using VBUS

Next, go to the Particle Web IDE and paste the code below into the editor.

Give your file a name and save it using the folder icon in the navigation panel.

Servo myservo;  // create servo object to control a servo 
                // a maximum of eight servo objects can be created

int pos = 0;    // variable to store the servo position

void setup() 
{ 
  Serial.begin(9600);  // Allow serial output for debugging
  myservo.attach(D8);  // attaches the servo on pin 8 to the servo object 
}


void loop() 
{ 
  Serial.printf("Incrementing...\n"); // Debug message
  for(pos = 0; pos < 180; pos += 1)   // goes from 0 degrees to 180 degrees 
  {                                   // in steps of 1 degree 
    myservo.write(pos);               // tell servo to go to position in variable 'pos' 
    delay(15);                        // waits 15ms for the servo to reach the position 
  } 
  Serial.printf("Decrementing...\n"); // Debug message
  for(pos = 180; pos>=1; pos-=1)      // goes from 180 degrees to 0 degrees 
  {                                
    myservo.write(pos);               // tell servo to go to position in variable 'pos' 
    delay(15);                        // waits 15ms for the servo to reach the position 
  } 
}

You can see the messages displayed on the serial port by starting the serial monitor with the command

particle serial monitor

If you need the servo to work reliably when the Argon is not connected to your computer, you will need to provide a second source of power. Usually this is some form or battery - a pack of four AA batteries, for example, provide a combined voltage of 6V. Please refer to the notes for further information.