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Brightness AnalogIn

In this example, we use PWM to adjust the brightness of an LED according to the position of the potentiometer.

What you need

  • SwiftIO Feather (or SwiftIO board)
  • Breadboard
  • Potentiometer
  • LED
  • 330ohm resistor
  • Jumper wires


  1. Place the potentiometer onto the breadboard. Connect the legs on the left to pin 3V3, connect the second leg to pin A0, and the third leg to pin GND.
  2. Place the LED onto the breadboard. The long leg of LED goes to D19 through a resistor. The short leg connects to GND.
circuit diagram

Example code

You can find the example code at the bottom left corner of IDE: example / SimpleIO / BrightnessAnalogIn.

// Read the analog input value and use it to set the PWM output to change the LED brightness.
// Import the library to enable the relevant classes and functions.
import SwiftIO

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

// Initialize an analog input and a digital output pin the components are connected to.
let sensor = AnalogIn(Id.A0)
let led = PWMOut(Id.PWM0A)

// Allow the LED brightness control all the time.
while true {
// Read the input voltage in percentage.
let value = sensor.readPercent()
// Light the LED by setting the duty cycle.
// Keep the current LED state for 200 millisecond.
sleep(ms: 200)

Code analysis

let value = sensor.readPercent()

There are three available methods to get analog values in different forms. In this case, you will need .readPercentage. It will return a percentage representing the ratio between actual voltage and reference voltage (3.3V). The value can then be used as duty cycle to set the LED brightness.


DigitalOut - set whether the pin output a high or low voltage.

AnalogIn - read the voltage from an analog pin.

MadBoard - find the corresponding pin id of your board.