2.1.3 Tilt Switch

Introduction

In this beginner-friendly project, you’ll learn how to detect when something is tilted or moved using a simple tilt switch sensor. This is commonly used in projects like burglar alarms, motion detectors, or automatic screen rotation on phones!

Components

What is a Tilt Switch?

A tilt switch is a simple but clever sensor that can detect when it’s been tilted or moved. Think of it like a digital spirit level that gives you a simple “tilted” or “not tilted” signal.

How does it work?

Inside the small cylindrical case, there’s a tiny metal ball that acts as the “switch”. Here’s the simple principle:

The Magic Inside:

When upright: The metal ball sits at the bottom, touching both metal contacts inside. This completes the electrical circuit (like a closed switch).
When tilted: The ball rolls away from the contacts, breaking the electrical connection (like an open switch).

Real-world analogy: Imagine a marble in a small tube. When you hold the tube straight up, the marble sits at the bottom touching both ends. When you tilt the tube, the marble rolls to one side and only touches one end (or neither).

Why is this useful? - Simple detection: You get a clear ON/OFF signal - No complex programming: Just check if the circuit is complete or broken - Very reliable: No moving parts to wear out (except the ball rolling) - Low power: Only uses power when you check its state

Connect

T-Board Name	physical	wiringPi	BCM
GPIO17	Pin 27	0	17
GPIO27	Pin 13	2	27
GPIO22	Pin 15	3	22

Code

For C Language User

Go to the code folder compile and run.

cd ~/super-starter-kit-for-raspberry-pi/c/2.1.3/

gcc 2.1.3_Tilt.c -lwiringPi

sudo ./a.out

Place the tilt horizontally, and the green LED will turns on. If you tilt it, “Tilt!” will be printed on the screen and the red LED will lights on. Place it horizontally again, and the green LED will turns on again.

This is the complete code

#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

// Define GPIO pins.
#define TILT_SWITCH_PIN 0
#define LED_GREEN_PIN   2
#define LED_RED_PIN     3

// Define an enumeration for LED colors for type-safe control.
typedef enum {
    OFF,
    GREEN,
    RED
} LedColor;

volatile int running = 1;

void signal_handler(int sig) {
    running = 0;
}

/**
* @brief Controls the state of the dual-color LED.
* @param color The desired color (OFF, GREEN, or RED).
*/
void set_led_color(LedColor color) {
    switch (color) {
        case GREEN:
            digitalWrite(LED_GREEN_PIN, HIGH);
            digitalWrite(LED_RED_PIN, LOW);
            break;
        case RED:
            digitalWrite(LED_GREEN_PIN, LOW);
            digitalWrite(LED_RED_PIN, HIGH);
            break;
        case OFF:
        default:
            digitalWrite(LED_GREEN_PIN, LOW);
            digitalWrite(LED_RED_PIN, LOW);
            break;
    }
}

/**
* @brief Initializes wiringPi and configures GPIO pins.
*/
void setup_hardware() {
    if (wiringPiSetup() == -1) {
        printf("Failed to setup wiringPi!\n");
        exit(1);
    }

    // Set up the tilt switch pin as an input with pull-up resistor
    pinMode(TILT_SWITCH_PIN, INPUT);
    pullUpDnControl(TILT_SWITCH_PIN, PUD_UP);  // 🔑 关键修复！

    // Set up LED pins as outputs.
    pinMode(LED_GREEN_PIN, OUTPUT);
    pinMode(LED_RED_PIN, OUTPUT);

    // Start with the green LED on to indicate normal state.
    set_led_color(GREEN);

    printf("Tilt switch hardware setup successful!\n");
    printf("Press Ctrl+C to stop...\n");
}

/**
* @brief Main loop to poll the tilt switch and update the LED.
*/
void poll_tilt_loop() {
    int last_tilt_state = -1; // Use -1 to force an initial update.

    while (running) {
        int current_tilt_state = digitalRead(TILT_SWITCH_PIN);

        // Simple debounce: check the pin state twice with a small delay
        delay(10);
        if (digitalRead(TILT_SWITCH_PIN) != current_tilt_state) {
            continue; // State changed during delay, skip this reading.
        }

        // Only update the LED and print a message if the state has changed.
        if (current_tilt_state != last_tilt_state) {
            if (current_tilt_state == LOW) {
                printf("Device is TILTED!\n");
                set_led_color(RED);
            } else {
                printf("Device is UPRIGHT.\n");
                set_led_color(GREEN);
            }
            last_tilt_state = current_tilt_state;
        }

        delay(50);
    }
}

/**
* @brief Clean up function
*/
void cleanup() {
    printf("\nCleaning up...\n");
    set_led_color(OFF);
    printf("LEDs turned off\n");
}

/**
* @brief Main function.
* @return Integer status code.
*/
int main(void) {
    signal(SIGINT, signal_handler);
    signal(SIGTERM, signal_handler);

    setup_hardware();
    poll_tilt_loop();
    cleanup();

    return 0;
}

For Python Language User

Go to the code folder and run.

cd ~/super-starter-kit-for-raspberry-pi/python

python 2.1.3_Tilt.py