Introduction: Magnetic Induction Safety Bike Lights. Nearly Invisible Design, Cheap, Waterproof and Battery Free!

This safety light system blinks as far the wheel spins: faster it spins, faster rate the leds blink. I'ts contactless so here is quite no friction. It uses magnetic induction so it’s battery and maintenance free, waterproof and really clean in design. Perfect for all purposes!
Here in Italy Reelight’s are quite famous, but i preferred to reply the system by myself: is cheaper, custom and more exciting! There are a lot of DIY versions of this kind of safety lights, and some of those were very inspiring for me. I want to share my design for you because it’s even simpler, cleaner and more reliable thanks to the heat shrinking tubes coating.

- MAINTEINANCE FREE, waterproof assembly gives high reliability
- CONTACTLESS, which means quite no friction (check out the video)
- CHEAP, you can take all materials from "scrap"
- SAFE, it lights up as the wheel spins

Will follow only some tips and hints, due the design is really simple and you can get it just from the images. For any doubt leave a comment!

Step 1: Materials, Tips, Hints


- neodymium magnets (i took two couples from a pair of old 6Gb HDDs)

- coil (i took one from a 12DC, 10A 250V Relay)

- mastic adhesive

- heat shrink tubes, in different diameters

- 5mm red leds, ~3V 20mA

- wire (coaxial stereo wire worked perfect for me)

- wooden icecream sticks

- cable ties


- everything you need to solder

- heat gun (or lighter)


- the center of the design is to use heat shrink tubes to wrap all components, and then fix it to frame with cable ties. Before heating the tubes, i filled those a bit with mastic glue, this way i obtained a watertight sealing (and these rainy days confirm this!)

- note that there is a convenient combination between magnets and coil orientation, try changing the led connection polarity.

- i found out it’s better to put less in parallel. Less leds, less the rotation speed to light them up.


- the coil produces alternate current. If you want to have a smoother blinking use a diode bridge to rectify the current and feed a capacitor placed in parallel with the leds.


- Reelight’s:

- best inspiring DIY project for me:


i’m using this since a week ago, 150km some under the rain, and is working good. During night i prefer to use another blinking tail light powered by batteries and a yellow reflective jacket, so i don’t think at this light as my only tail light, but in some situations it could be. Tail light blink from 4kph, this means it works also pushing the bike walking!

Hope you enjoy this project, and do even better!

Cheers from Italy!


**EDIT (8th dec) ~400km, some under rain and some under 0°C, and still working :) Average speed ~27kph, Max <60kph

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