DIY Smart Brake Light: Build a G-Force Sensing Bike Light

#include <Adafruit_NeoPixel.h>
#include <Adafruit_MPU6050.h>
#include <Adafruit_Sensor.h>
#include <Wire.h>

// --- CONFIGURATION ---
#define LED_PIN    6       // Pin connected to Neopixel Ring
#define LED_COUNT  12      // Number of LEDs on your ring
#define BRIGHT_DIM 30      // Brightness for cruising (0-255)
#define BRIGHT_MAX 255     // Brightness for braking (0-255)

// Sensitivity Threshold (Negative value for deceleration)
// Adjust this based on road tests. -2.0 is usually a good start.
#define BRAKE_THRESHOLD -2.0 

// Hardware Objects
Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);
Adafruit_MPU6050 mpu;

// Global Variables for Smoothing
float calibratedZero = 0;
float currentAccel = 0;
float alpha = 0.9; // Smoothing factor (Higher = smoother but more lag)

void setup() {
  Serial.begin(115200);

  // 1. Initialize LEDs
  strip.begin();
  strip.show(); 
  strip.setBrightness(BRIGHT_MAX);

  // 2. Initialize Sensor
  if (!mpu.begin()) {
    Serial.println("Failed to find MPU6050 chip");
    while (1) {
      // Flash Red to indicate error
      colorWipe(strip.Color(255, 0, 0), 50);
      delay(500);
      colorWipe(strip.Color(0, 0, 0), 50);
      delay(500);
    }
  }

  // 3. Calibration Sequence
  // Bike must be still during this phase!
  Serial.println("Calibrating... Keep bike still.");
  float total = 0;
  for(int i=0; i<100; i++) {
    sensors_event_t a, g, temp;
    mpu.getEvent(&a, &g, &temp);
    // Assuming Y-axis is pointing forward/backward
    total += a.acceleration.y; 
    delay(10);
  }
  calibratedZero = total / 100.0;
  
  // Flash Green to indicate ready
  colorWipe(strip.Color(0, 255, 0), 20);
  delay(500);
}

void loop() {
  sensors_event_t a, g, temp;
  mpu.getEvent(&a, &g, &temp);

  // Get raw Y-axis acceleration (longitudinal)
  float rawAccel = a.acceleration.y;

  // Subtract the calibration offset
  float correctedAccel = rawAccel - calibratedZero;

  // Apply Low Pass Filter (Smoothing)
  currentAccel = (currentAccel * alpha) + (correctedAccel * (1.0 - alpha));

  // --- LOGIC CHECK ---
  // If deceleration is stronger than threshold
  if (currentAccel < BRAKE_THRESHOLD) {
    // BRAKING: All Red, Full Brightness
    setAllColor(255, 0, 0); 
  } else {
    // CRUISING: Red, Dimmed (Tail light mode)
    // Optional: Add a "Knight Rider" scanner effect here for visibility
    setAllColor(BRIGHT_DIM, 0, 0); 
  }

  delay(50); // Loop rate ~20Hz
}

// --- HELPER FUNCTIONS ---

// Set all LEDs to a specific RGB color
void setAllColor(int r, int g, int b) {
  for(int i=0; i