Introduction: Bike Wheel Induction Safety Light


It's a wheel spoke mountable safety light for your bike that doesn't need batteries. Ever. It also has smart on/off function. Light turns on when you start moving and turns of about 5 seconds after you stop moving.


No batteries needed. Never end up in dark with your bike.

Smart on/off function. Light turns on when you start moving and turns of about 5 seconds after you stop moving.

Custom inscription/logo/colors.

Parts list

(1) Neodymium magnet 2x

Dimensions: Diameter from 10 to 12mm, thickness from 4 to 10mm.

Source: Old HDD, ebay

(2) Spoke mount left - 3d printed part

Source: Print it yourself. All 3D models freely available at thingiverse: or buy here:

(3) Coil housing 2x - 3d printed part

(4) Spoke mount right - 3d printed part

(5) Universal magnet mount upper - 3d printed part

(6) M3 X 35 screw and a nut

(7) Universal magnet mount lower - 3d printed part

(8) Magnet housing screw - 3d printed part

(9) Locking nut - 3d printed part

(10) Adjustment screw - 3d printed part

(11) 5 mm white LED

Source: Any decent hardware store or ebay

(12) 1000µF, 16V capacitor.

Source: Hardware stores, in old electronics components, ebay

(13) 1 k Ohm, 1/4W resistor

Source: Any decent hardware store or ebay

(14) Diode bridge

Source: recycled electronics, ebay

How to make one:

You can use 4001, 4148... diodes, but for maximum performance use Schottky diodes (1N5818 or similar)

(15) 24V or 12V relay coil

Coil resistance should be aprox. from 250 to 1800 Ohms

Source: Old relays, ebay

(16) Main housing - 3d printed part

Step 1:

If you're using square relay adapter go to step 4.

If you're using a coil from an old 24V relay simply saw on the line marked with yellow on image 1. The only mistake you can make is to cut to deep ruining the coil. After the metal carrier falls apart you'll end up with what you need. Trim plastic flanges on both sides to make them round. Solder everything together based on scheme diagram (image 2) and you'll end up with a compact unit seen right on image 1. Coil orientation after assembly needs to be the same as left on image 1 (pre assembly).

Solder 1k resistor to positive side of 5mm LED as shown on image 3.

Step 2:

You need to drill a 6mm hole in to inner threaded part of main housing. There is already a 6mm indentation on the printed housing. Best way to do it is with a dremel, hot tip or a bore.

Insert LED with resistor in to drilled hole. Place coil-diode bridge-capacitor assembly in coil housing 1 and screw it in to main housing as shown on image 4.

Solder positive side of LED to positive side of capacitor and negative to negative.

Screw coil housing 2 in. Spoke mounted part is done. If you want to make it 100% rain resistant spray it with 1 rich coat of plastic acrylic paint primer and minimal 2 coats of acrylic lacquer.

Step 3:

Insert Neodymium magnet(s) on to magnet housing. You can stack anything from 4 to 12 mm of magnets in there. If you use more/stronger magnets then voltage induced in coil will be higher and led will shine stronger. This allows you to custom tune brightness. Coil housing has thread on inner and also outer side. After fitting the magnets simply secure by screwing adjustment screw in to magnet housing (image5).

Assemble universal magnet mount as shown on image 6.

Slide wheel safety LED on wheel spokes.

Attach magnet mount to bike frame. It's quite flexible so should fit on wide variety frame profiles and places.

Adjust everything so the coil passes the magnet with 1-2mm clearance (images 7,8,9).

You're done. Stay safe.

Step 4: Simplified Way of Installing Electronic Components

You have 3 different coil housing options to use depending on your coil size. Simplest to use is coil_housing_square with coil_housing_square_cover. This two files house a standard 24V, 10A relay coil such as: SRD-24VDC-SL-C. You don't have to "operate" the relay to get the coil out, you simply sand of one part of the relay and insert the whole relay. coil_housing_square has a support modeled on the internal side which you simply snap off or drill out after printing. Its the only model that has or needs any kind of support.

Check image 10 for following steps:

1. Relay before sanding.

2. Sand off the relay until you reach coil core. You will end up with relay about 12-13mm thick.

3. Solder the rectifier to the coil.

4. Insert the coil+rectifier to the new square coil adapter.

5. Insert the led diode with soldered resistor in the main housing then screw in the square coil adapter.

6. Solder the positive leads of diode and rectifier to positive capacitor side and negative leads of capacitor and rectifier to capacitor negative.

7. Tuck in all the wires. Screw in the new square coil adapter cover on and you are done.