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![bikelight_overview](img/bikelight_overview.jpg)
It's a blinky red light for the back of my bike helmet.
![bikelight](img/bikelight.mp4)
The circuit uses an ATtiny412 to control four red LEDs, along with a Microchip MCP73831 lipo charge controller for battery management and a micro-USB jack for charging.
![bikelight_schematic](img/bikelight_schematic.png)
![bikelight_pcb](img/bikelight_pcb.png)
The circuit is designed to be milled on a single sided chunk of FR1 using a 1/64" end mill. If you use [mods](mods.cba.mit.edu), the three layer *.svg files (holes, outline, and traces) are in the /pcb directory. After assembling and programming with [pyupdi](https://github.com/mraardvark/pyupdi) and an FTDI cable, I masked off the USB jack and slide switch and sprayed it with a few coats of clear varnish.
![bikelight_pcb_img](img/bikelight_pcb_img.jpg)
The pcb attaches using M3 hardware to two laser cut acetal clips, which then snap into [my helmet](https://www.bernhelmets.com/collections/bike/products/summer-watts?variant=13190223200315). If you have the same model, this will probably work for you too, otherwise you'll need to figure something else out. Laser cut files for these parts are in the /cad directory, intended to be cut from 2.5 mm acetal.
![bikelight_mtg](img/bikelight_mtg.jpg)
![bikelight_mtg2](img/bikelight_mtg2.jpg)
I used a 1200 mAH lipo battery since we had a few on hand; it's secured to the rear of the pcb using VHB tape. I snagged a JST PH off a spare Feather, but if you plan ahead you can buy the part [here](https://www.adafruit.com/product/1769). Note that lipo batteries are inherently dangerous, so don't build this circuit unless you're familiar with their quirks (and make sure to use one with a built-in protection circuit). Yes, if my helmet ever actually has to do its job, my head will likely catch fire.
![bikelight_back](img/bikelight_back.jpg)
bikelight! blink blink blink blink blink