The servo motor has three leads. The color of the leads varies between servo motors, but the red lead is always 5V and GND will either be black or brown. The other lead is the control lead and this is usually orange or yellow. This control lead is connected to digital pin 9.
The servo is conveniently terminated in a socket into which we can push jumper wires, to link it to the breadboard and then to the Arduino.
If servo Misbehaves
Your servo may behave erratically, and you may find that this only happens when the Arduino is plugged into certain USB ports. This is because the servo draws quite a lot of power, especially as the motor is starting up, and this sudden high demand can be enough to drop the voltage on the Arduino board, so that it resets itself.
If this happens, then you can usually cure it by adding a high value capacitor (470uF or greater) between GND and 5V on the breadboard.
The capacitor acts as a reservoir of electricity for the motor to use, so that when it starts, it takes charge from the capacitor as well as the Arduino supply.
The longer lead of the capacitor is the positive lead and this should be connected to 5V. The negative lead is also often marked with a '-' symbol.
Load up the following sketch onto your Arduino. You should find that the servo immediately begins to turn first in one direction and then back in the other.
The sketch is based on the standard 'sweep' sketch that you can find in the Arduino Examples under the folder 'servo'.
#include <Servo.h>
int servoPin = 9;
Servo servo;
int angle = 0; // servo position in degrees
void setup()
{
servo.attach(servoPin);
}
void loop()
{
// scan from 0 to 180 degrees
for(angle = 0; angle < 180; angle++)
{
servo.write(angle);
delay(15);
}
// now scan back from 180 to 0 degrees
for(angle = 180; angle > 0; angle--)
{
servo.write(angle);
delay(15);
}
}
Servo motors are controlled by a series of pulses and to make it easy to use them, an Arduino library has been created so that you can just instruct the servo to turn to a particular angle.
Arduino SERVO knob
You just need to add the pot and a lead from its slider to A0 on the Arduino
#include <Servo.h>
int potPin = 0;
int servoPin = 9;
Servo servo;
void setup()
{
servo.attach(servoPin);
}
void loop()
{
int reading = analogRead(potPin); // 0 to 1023
int angle = reading / 6; // 0 to 180-ish
servo.write(angle);
}
There is now a second variable called 'potPin'.
To set the position of the servo, we take an analog reading from A0. This gives us a value of between 0 and 1023. Since the servo can only rotate through 180 degrees, we need to scale this down. Dividing it by six will give us an angle between 0 and 170, which will do just fine.
The position of the servo motor is set by the length of a pulse. The servo expects to receive a pulse roughly every 20 milliseconds. If that pulse is high for 1 millisecond, then the servo angle will be zero, if it is 1.5 milliseconds, then it will be at its centre position and if it is 2 milliseconds it will be at 180 degrees.The end points of the servo can vary and many servos only turn through about 170 degrees. You can also buy 'continuous' servos that can rotate through the full 360 degrees.
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