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FBTA
Fake Bike Theft Alarm
This
fun project isn't exactly ham radio related, but it does give you tips
how to safely charge a small Li-ion battery with a USB charger and guide
you how to blink a LED efficiently.
The idea of this project is to install a flashing LED inside the end of a bicycle handlebar. This may scare a thief and prevent the bike from being stolen. You only need to make a hole in the grip for the LED. Typically a handlebar inner diameter is 19mm, this PCB needs 18m. 
The
estimated operating time is one year with a 800mAh size 14500 (AA) 3.7V
Li-ion battery. This
means that it only needs to be charged once a year and this can be done
via the USB-C connector. The charging time is abt 2.5 hours, follow the
status LEDs.
The blinking LED circuit is a Schmitt trigger oscillator which drives a LED by means of a N-MOSFET. 
The charger is using a Microchip Li-ion charger IC. It makes preconditioning, constant current and finally constant 4.2V voltage charging until the current is low enough, which after it stops charging. The IC provides also status LED drive for charge and full charged condition. See more in the schematics. Downloads - Schematics - BOM - Layout - Gerber files Update 2024-12-13 OH7SV Back to OH7SV projects |