Group riding would be much safer if bikes had brake lights. The lack of brake lighting on bicycles has lead to the audio cues of "SLOWING" or "STOPPING" being shouted at every turn. While this may enhance safety, it certainly cuts into the serenity of a ride.
This project offers a viable solution that can increase both safety and serenity on a group ride. With embedded programming made easy by the Arduino integrated development environment, electronics getting smaller, more capable, and cheaper, this project is possible for the do-it-yourselfer.
BEBL Challenge! Be the first, and get your hardware cost reimbursed. I will award a $35 reimbursement, by mail or PayPal, to the first person to post a video online that demonstrates a functioning and mounted Bar End Brake Light made from these plans. Looking forward to seeing your project.
Other than the obvious criterion -- light up when braking, I wanted this light to look cool, cool enough to mount on any expensive racing bike. This rules out any visible wiring. I also wanted the light to be portable, meaning it will work on more than one bike. Thus no brake-lever specific triggering should be used.
The final design is centered around a 3-axis accelerometer board provided by Pololu.com. This product is simple to use with an Arduino, small enough to fit inside the handle bars, and best of all cheap at $15. Also, this accel has an on-board voltage regulator that we will take advantage of to power the whole circuit.
The processing takes place in an ATmega328 programmed with Arduino. These chips can be also be programmed directly in C, but Arduino takes care of a lot of setup and generally makes programming less tedious. Arduino has everything this project needs. The ATmega168 would probably suffice for this project but the ATmeta328 at $1 more, provides 2X the program space.
Mounting the computer inside the handlebars provides an enclosure for the project.
Step 1: Schematic, layout, and bill of materials
Let me know if you are interested in a printed board. We can combine orders and save!
Accel -- 3-axis accel breakout $15
6V battery -- Lithium 28L $5 each
S2 -- Surface mount right angle switch $1
IC1 -- AVR ATMega328 w/ arduino bootloader $5.50 (Consider getting this from ladyada.com, for her supped up bootloader)
LED1 -- Super bright LED red $1 each x 2
Osc1 -- 16 MHz oscillator $1
28-pin DIP socket $1.50
C1, C2 -- .1 uF ceramic cap
R1, R2 -- 220 Ohm resistor
Project board $2
Bar tape and plugs.
Total cost around $35, battery included. I'm not including the cost of the bar tape, since you need to have that anyway.