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It's not fair. 

Your car shows brake lights when it brakes. Some cool cars turn their lights on when you approach your car at night. Some really cool cars change the intensity of brake lights when they brake hard. 

My bike has a red light that turns on when you press a button. 

NOT FAIR. 

For my FedEx Day project (a day where our company lets us make anything for 'next day delivery'), I brought my bike into the future with the help of a coworker and a local design firm called Altitude. My coworker helped with the Bluetooth programming, and Altitude designed+fabricated the 3D printed rear light mount and brake detection assembly. 

Check out the final result:

Rear Light

1. The user brakes, which completes a circuit on the Arduino.
2. The Arduino reads the acceleration value from the accelerometer and calculates a "braking power" number based on how fast you're stopping.
3. The Arduino sets RGB values on the NeoPixel ring based on the braking power. Faster braking = brighter lights.

Front Light

1. The user pairs their phone one time with the front light via Bluetooth.
2. The Arduino periodically checks the Bluetooth module to see if a phone is connected.
3. If a phone is connected, the Arduino turns on a light.
4. The Arduino keeps the light on until no vibration has been detected by the accelerometer for over a minute and the phone is no longer paired.

Parts List

• Arduino Uno R3 Microcontroller 
• Adafruit Triple-Axis Accelerometer - 2/4/8g @ 14-bit - MMA8451
• Adafruit 12 RGB LED Neopixel Ring
• DSD TECH HC-05 Bluetooth Serial Pass-through Module Wireless Serial Communication with Button for Arduino
• 9V snap connector, and 8AA battery pack
• Triangle Saddle Bag 
• Wires to connect components
• Custom assembly on brake cable to complete circuit while braking
• Custom 3D printed housing for Adafruit 12 RGB LED Neopixel Ring

Open Items

• I only had 8 hours to get this all done, so the front light was pretty sketchy. I'd like to move the Bluetooth hardware onto the main Arduino in the bike bag, and run a wire to a better looking front bike light. 
• Although functional, the code that detects braking is pretty simple and could be made more robust to detect braking on hills. It could also flash the LED ring after quickly braking. 
• Eventually, I'd be nice to redo this on a smaller Arduino, like the Arduino Nano, and to move over to Lithium cells for the battery so I could mount everything on the rear seat post.
• Even further out: I'd love to shrink this all down into a custom board, have the front light wirelessly communicate with the rear light, and have the brake detection mechanical assembly be a little more robust which would basically turn this little hack into a real product.

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