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Bluetooth-enabled bicycle turn signal

A turn signal for bikes!


After commuting to work every day on my bicycle, I decided that I needed a better way to signal my turns. Sticking my arms out can be dangerous, especially if you're riding downhill in the rain (as is common in Vancouver).

I had recently got an Arduino and wanted to embark on my first project, so I decided to kill two birds with one stone!

I wanted something waterproof that I can use in the rain, and something detachable so it wouldn't get stolen, it needed to be detachable/wireless.

The plan was to have a couple of switches embedded into the handlebars (for power and for turn signal), use a Bluetooth transmitter (HC-05) for communication, and have an Arduino Nano to control it all with an 18650 lithium-ion battery (controlled with a 134N3P chip) for power. On the other end of the bike, there are two 8x8 LED matrices controlled by MAX7219 controllers, a Bluetooth receiver (HC-05), an ATMEGA328P chip to control all the components and an 18650 (or 14500) lithium-ion battery for power. I also added a Qi wireless charging receiver to charge the battery without opening the lights enclosure.

Action shots

Here's a gif of it in action:

it's working!

A closeup of the updated slim case with all the gubbins: slim_case.jpg moving

If you don't like my boring arrows, make any indicator animation you want using my 8x8 LED byte generator found on my LED_byte_matrix_generator repo

Full parts and tools requirements can be found on the page

Wiring diagrams

Diagram for handlebar/controller:

Inside the handlebars

Diagram for lights enclosure:

lights wiring

Setup instructions:

  • Set up the HC-05 Bluetooth modules to pair with each other using a master-slave setup (instructions)
    • Other Bluetooth modules with similar functionality can be used
  • Upload code for the lights and the handlebars to the Arduino Nano (or any other ATMEGA328P based chip)
  • Wire everything up according to the wiring diagrams
    • if using a reed switch to control power to the lights, you'll need a magnet

Variation/upgrade ideas

  • Reed switch to control power to the lights. If your case is too slim for a toggle switch (like my latest iteration) or you're worried about the waterproof-ness of the case, a reed switch could be used.

    • New wiring diagram: with reed switch
    • A magnet attached to the light mount can turn the lights on and the lights can be turned off by taking the lights off the mount
    • Or a second magnet can be used to change the flux path and open the reed switch like so: flux change
  • Neopixel rings and jewels as a turn signal, like a car with the outer ring in red and the inner jewel lit up amber and flashing when turning

    neopixel idea

  • Add an accelerometer to detect slowing down and display a slowing down animation or flash amber lights

  • Use large/bright LED strips on the seatstays instead of LED matrix for better visibility Because the LED matrix is hard to see, especially in the daylight, a better/more obvious variant of this project can be built with bright LED strips attached to the seatstays of the bike. While this will improve visibility, it won't be as removable. Another similar idea is to use bright LED strips protruding as rods (horizontally, left and right) and blink them like this.

Pictures of the build


Internals of handlebars

Note: Bluetooth module, Arduino Nano and PCB separated from battery by a long ~1m cable

Image of handlebar batteries:

handlebar batteries

Testing lights before gluing everything and closing the case:


Mounted on my bike:


Message me for more details if you want to make one for yourself

Thanks for reading!


Lights enclosure with breadboards wired up:


Qi wireless charger attached to battery pack:


Fully assembled: