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2.7 Toggle Left and Right

In this lesson, we’ll learn how to use a slide switch with the Raspberry Pi Pico 2 W to detect its position (left or right) and perform actions based on that. A slide switch is a simple mechanical device that connects the common (middle) pin to one of the two outer pins depending on its position.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	PURCHASE LINK
Pico 2 W Starter Kit	450+	Pico 2 W Kit

You can also buy them separately from the links below.

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Getting to Know Pico 2 W	1
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Resistor	1(10KΩ)	BUY
6	Capacitor	1(104)	BUY
7	Slide Switch	1

Understanding the Slide Switch

img_slide

A slide switch has three pins:

Pin 1: Connected when the switch is toggled to one side (e.g., left)
Pin 2: Common pin (middle pin)
Pin 3: Connected when the switch is toggled to the other side (e.g., right)

By reading the voltage on the common pin, we can determine the position of the switch.

Schematic

sch_slide

GP14 will get a different level, when you toggle the slide switch to the right or left.

The purpose of the 10K resistor is to keep the GP14 low during toggling (not toggling to the far left and not toggling to the far right).

When you toggle the switch, the mechanical contacts can cause rapid, noisy signals known as “bounce.” The capacitor connected between GP14 and GND helps to filter out these rapid fluctuations, providing a cleaner signal.

Switch Toggled to the Right:
- Pin 2 (GP14) is connected to 3.3V through Pin 1.
- The GPIO pin reads HIGH (1).
Switch Toggled to the Left:
- Pin 2 (GP14) is connected to GND through Pin 3.
- The GPIO pin reads LOW (0).
Switch in the Middle Position:
- Pin 2 (GP14) is not connected to either 3.3V or GND.
- The pull-down resistor keeps the GPIO pin at LOW (0).
- The capacitor helps to reduce switch bounce (noise due to mechanical movement).

Wiring

wiring_slide

Writing the Code

Note

You can open the file 2.7_toggle_left_right.ino under the path of pico-2w-kit-main/arduino/2.7_toggle_left_right.
Or copy this code into Arduino IDE.
Don’t forget to select the board(Raspberry Pi Pico) and the correct port before clicking the Upload button.

const int switchPin = 14;   // GPIO pin connected to the slide switch
int switchState = 0;

void setup() {
  Serial.begin(115200);       // Initialize Serial Monitor at 115200 baud
  pinMode(switchPin, INPUT);  // Set the switch pin as input
}

void loop() {
  switchState = digitalRead(switchPin);  // Read the state of the switch

  if (switchState == HIGH) {
    Serial.println("ON");   // Switch toggled to the left
  } else {
    Serial.println("OFF");  // Switch toggled to the right
  }
  delay(200);  // Small delay to avoid flooding the Serial Monitor
}

When the code is running and the Serial Monitor is open:

Prints “ON” when the switch is toggled to the left and “OFF” when toggled to the right.

Understanding the Code

Initializing Serial Communication:

Starts serial communication at a baud rate of 115200. This allows us to print messages to the Serial Monitor.
```
Serial.begin(115200);
```
Setting Up the Switch Pin:

Configures switchPin (GP14) as an input to read the switch state.
```
pinMode(switchPin, INPUT);
```
Reading the Switch State:

Reads the current state of the switch. It will be HIGH when toggled to the right and LOW when toggled to the left or in the middle position due to the pull-down resistor.
```
switchState = digitalRead(switchPin);
```
Responding to Switch Position:

Prints “ON” when the switch is toggled to the left (GP14 reads HIGH) and “OFF” when toggled to the right (GP14 reads LOW).
```
if (switchState == HIGH) {
  Serial.println("ON");
} else {
  Serial.println("OFF");
}
```

Alternative: Using Internal Pull-Up Resistor

If you prefer to simplify the circuit and reduce the number of components, you can use the internal pull-up resistor of the Pico. However, please note that traditional Arduino boards do not support internal pull-down resistors, only internal pull-up resistors. The Raspberry Pi Pico does support INPUT_PULLDOWN, but in the Arduino environment, its support may vary. For this example, we’ll use INPUT_PULLUP.

Circuit Modifications:
- Remove the External 10KΩ Resistor and Capacitor.
- Slide Switch Connections:
  - Pin 1: Connect to GND on the Pico.
  - Pin 2: Connect to GP14 on the Pico.
  - Pin 3: Leave unconnected or connect to GND (since we’re using the internal pull-up).

Code Modifications:

const int switchPin = 14;   // GPIO pin connected to the slide switch
int switchState = 0;

void setup() {
  Serial.begin(115200);          // Initialize Serial Monitor at 115200 baud
  pinMode(switchPin, INPUT_PULLUP);  // Enable internal pull-up resistor
}

void loop() {
  switchState = digitalRead(switchPin);  // Read the state of the switch

  if (switchState == LOW) {
    Serial.println("ON");    // Switch connected to GND, toggled to the right
  } else {
    Serial.println("OFF");   // Switch not connected, reads HIGH due to pull-up
  }
  delay(200);  // Small delay to avoid flooding the Serial Monitor
}

Conclusion

In this lesson, you’ve learned how to use a slide switch with the Raspberry Pi Pico to detect its position and perform actions based on that. You’ve also seen how to implement a pull-down resistor in the circuit to ensure reliable readings and how to use the internal pull-up resistor to simplify the circuit.

Further Exploration

Control an LED: Modify the code to turn an LED on or off based on the switch position.
Multiple Switches: Try adding more switches to control different actions.
Debouncing: Implement software debouncing to handle any residual switch bounce.