Using PWM to control a servo

You can use the PWM output, or more technically PPM (Pulse Position Modulation) - to control a servo.

Let’s start with connecting a servo:

We will use port 11, as typically we would use one of PWM-capable pins for servo control, there are alternatives though.

Starting code below:

#include <Arduino.h>
#include <Servo.h>

Servo myservo;
void setup(){
  myservo.attach(11);
}

void loop(){
  for(uint16_t i = 0; i <= 180 i++){
    myservo.write(i);
    delay(20);
  }
  for(uint16_t i = 180; i >= 0 i--){
    myservo.write(i);
    delay(20);
  }
  delay(1000);
}

Let’s try to build, and… whoops! Most likely the code has failed to build due to unavailable libraries:

Luckily PlatformIO makes it ieasy for us to solve the issue, let’s try to do what they suggest and use the search on their website: https://platformio.org/lib/search?query=header:Servo.h.

Usually it’s worthy checking out most downloaded libraries first:

If you go to the “Installation” tab you should see the recommended way to add the library as a dependency to your project.

Let’s open up platformio.ini and add it:

Right under framework = arduino let’s paste the following:

lib_deps =
    arduino-libraries/Servo @ ^1.1.8

Let’s try again to build, upload and verify. Now the servo should be moving from 0 to 180 degress and then down from 180 to 0.

TASK: Servo action after a button press

Let’s try to build a simple logic with the servo that will:

set up an interrupt for a button press
move the servo quickly to 100 degrees
hold for 3 seconds
move the servo slowly to 140 degrees
hold for 1 second
move the servo quickly back to 0 degrees The imagined use case is that you are opening something up based on a button press.

Suggestions:

if you just set the servo to given angle it’s reaction could be too dynamic, let’s try to use loops to make the movement with a manageable speed.
rather than using three separate loops, you could write a single function that would move the servo from given angle to given angle, with a specific speed,

Using digital gpio to control a stepper motor

It is also possible to use plain digital GPIO to control a stepper motor via an external driver.

Please connect the stepper motor driver to the Arduino:

IN1 - GPIO 11
IN2 - GPIO 10
IN3 - GPIO 9
IN4 - GPIO 8
5V - 5V
GND - GND

And let’s try the starting code:

#include <Arduino.h>
#include <Stepper.h>
const int stepsPerRev = 200;
Stepper myStepper(stepsPerRev, 8, 9, 10, 11);

void setup(){
  myStepper.setSpeed(50);
}

void loop(){
  myStepper.step(stepsPerRev / 100);
}

Using PWM to control a buzzer

PWM can also be used to generate simple, square wave tones and emit sounds with a buzzer.

You can just connect it to any of the PWM capable pins and ground:

Starting code would be as simple as this:

#include <Arduino.h>
#define BUZZER_PIN 9
void setup(){
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop(){
  tone(BUZZER_PIN, 440, 100);
  delay(1000);
}

Ultrasonic distance measurement

Let’s try to use an ultrasonic distance measurement module. It works on a simple principle of sending and ultrasound signal and waiting for it to bounce back.

To connect it to your board you need to attach power (5V & GND) and two digital signals - TRIG and ECHO. Any digital pins can be used.

Example wiring on a diagram:

To work with the sensor you will need a proper library. A quick search on platformio would bring up: https://platformio.org/lib/show/1507/Ultrasonic

Let’s try to add that library to your project (edit platformio.ini) and try a basic example.

#include <Arduino.h>
#include <Ultrasonic.h>

Ultrasonic ultrasonic(12, 13);

void setup() {
  Serial.begin(9600);
  ultrasonic.setTimeout(40000UL);
}

void loop() {
  Serial.print("Distance [cm]: ");
  Serial.println(ultrasonic.read());
  delay(1000);
}

Let’s try to build, upload & verify the serial output.

TASK: Lowering the sensor timeout for robustness

Important note - observe what happens when there is nothing in front of the sensor - how long it takes for the code to timeout practically blocking the code from moving with any other work.

If you have an use-case that doesn’t really require full sensor range (typically up to 200cm), but you only care if there is something close to the sensor - you can address that issue setting the timeout lower.

Let’s try to modify

TASK: build a complete parking sensor solution

Now you should have all the tools required to build a fully functional parking sensor.

Let’s try to implement the following:

ultrasonic sensor with distance measurement in the range of 0-50cm
a few LEDs displaying the measured distance
buzzer that will change its tone and period between beeps when the object gets closer

Next steps

Now let’s continue to work with digital I2C bus and an OLED screen

Using PWM to control a servo#

TASK: Servo action after a button press#

Using digital gpio to control a stepper motor#

Using PWM to control a buzzer#

Ultrasonic distance measurement#

TASK: Lowering the sensor timeout for robustness#

TASK: build a complete parking sensor solution#

Next steps#