Control a Servo Using Swift Language

In this mission, you will use another kind of motor, the servo motor. The angle of its arm could change with the potentiometer

Step 1: What You Will Need

The parts you will need are all included in the Maker kit.

• SwiftIO board
• Shield
• Servo
• Potentiometer module
• 4-pin cable

Step 2: The Servo Motor

The servo motor could adjust its arm's position according to the signal. You could set PWM output to control it. This servo requires a pulse every 20ms. And the duration of each pulse determines the position of the arm:

• If the high voltage lasts for 0.5ms, the arm will be at 0 degrees.
• If the high voltage lasts for 2.5ms, the arm will be at 180 degrees.
• If the high voltage lasts for 1.5ms, the arm will be at 90 degrees.

Note: this servo needs the pulse to be in the range of 0.5 to 2.5ms. You may also meet other servos that need the pulse in 1 to 2ms.

Step 3: The Circuit

Place the shield on top of your SwiftIO board.

Connect the potentiometer module to pin A0 using a 4-pin cable.

Connect the servo to the pin PWM4A. The servo has three wires: the ground wire is brown, the power wire is red and the signal wire is orange.

Step 4: The Code

/* Import the SwiftIO library to use everything in it. */
import SwiftIO

/* Import the board library to use the Id of the specific board. */
import SwiftIOBoard

/* Initialize the analog pin. */
let a0 = AnalogIn(Id.A0) 

let servo = PWMOut(Id.PWM4A)

while true {
    /* Read the analog value and return a value between 0.0 and 1.0. */
    let value = a0.readPercent() 

    /* Calculate the value to get the pulse duration. 
    Each cycle of the signal lasts for 20 milliseconds.
    The pulse should last between 0.5 and 2.5 ms to activate the servo. 
    With a 0.5ms pulse, the servo will turn to 0 degrees and with a 2.5ms pulse, it will at 180 degrees. 
    In between, it is at an angle between 0–180. */
    let pulse = Int(500 + 2000 * value) 

    /* Set the servo position according to the scaled value. */
    servo.set(period: 20000, pulse: pulse) 
    sleep(ms: 20)
}

Step 5: Code Analysis

import SwiftIO
import SwiftIOBoard

Import the two libraries: ​SwiftIO and ​SwiftIOBoard.

let a0 = AnalogIn(Id.A0)
let servo = PWMOut(Id.PWM4A)

Initialize the analog pin A0 for the potentiometer and the PWM pin PWM4A for the motor.

let value = a0.readPercent() 
let pulse = Int(500 + 2000 * value)
servo.set(period: 20000, pulse: pulse)
sleep(ms: 20)

In the dead loop, read the input value in percentage, so you get a value between 0 and 1.

You will use this method set(period:pulse:) to set the PWM. The period is measured in microseconds, so it is 20000us. The pulse should be the number between 0.5ms to 2.5ms. So the value will be matched into this range by doing some calculations.

Step 6: Run the Project

As you turn the potentiometer, the servo arm will move to a different angle.