Bike Wheel Induction Safety Light




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.

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84 Discussions


1 year ago

Just ordered a kit. One of the best instructables I've seen. Well thought out, clearly explained, modular and hackable. Nicely done.

I would do it in reverse - not the spokes to light but the rear light to be a red LED powered by dynamo/magnet on the spoke(s) .

Also replacing the rectifier is a great idea and the resistor is not needed you might not make too much current to burn the LED - if you do - then put more LEDs in parallel.

Also Joule Thief circuit might be e good idea and super-capacitor / ultra-capacitor.

Great - good work.

2 replies

NO. The LED's are "voltage"- sensitive, that is: a standard (red) led has a forward voltage of ~ 2,1volt, and can manage ~20milliamps max. So, if you put higher voltage to the ledneed to "eat up" the owervoltage e.g. : if you put 6Volt on the led you need to eat up 6V-2,2V=3,8V and with 20mA that will be R=U/I => 3,8V/0,02A => ~ 190R. Therefore, it doesn't help if you put led's in parallel, the only thing you achvive with that is you have to eat up more Amps. But putting led's in serial you again have a problem, you get them to light with 2,2V+2,2V=4,8V?? Pleeeeease.... use a resistor

The idea is to increase visibility by having a rotating light source.

The idea is good & doable. But go and check After
checking that, please continue from there giving us 'ables to build such
of our own?

why did u give us that link? it goes to a company making phones. why add spam in the instructables?

It surely does not go to any "phonemaker"??? and the bicykle there

Why do you use rectifiers, caused too much loss? You must switch instead two led diodes antiparallel.




2 years ago

Looking at the multicolor LED in ianmcmill's video, how about having a red LED turn on when slowing down or stopping (staying on for more than few seconds) while the white LED turns on as you speed along ?

First thank you for the great tutorial. I tried to do it on my own but it didnt work out. I bought a 24V relay, 220 ohm (FIN 40.52.8 24V) and some neodymium magnets (N48, 15x5mm). But the coil only works when the magnet TOUCHES the coil. @ianmcmill which relay coil did you use exactly? Thanks for the help.

1 reply

Check Step 4. I used: SRD-24VDC-SL-C. I recently designed additional coil housing which makes it really easy to install and is back compatible with the rest of the design. You can use the whole relay without having to remove the coil. Or just remove the coil and use old 3d files.

I designed 2 new components which simplify installing electronic components a lot. Check step 4 for details.

This is awesome! I made one and it works great. Can anyone explain the selection of the optimal relay coil? There are a lot of different coils out there. Is the voltage rating of the coil important or just the resistance? Does it have to be a relay coil or would any inductor work? Which type of coil produces the most power for a given magnet and magnet distance (geometry)? What is the lightest weight coil or coil-geometry that will generate the most power? Thanks.

5 replies

Quite few people requested full kit for this project so I'm actually testing coils at the moment to source a cheap and efficient one. Those 24V power relay ones are to expensive. Ill get back to when i figure something out.

I have tried 2 relays.

The first and second picture shows an Omron 24V relay. The coil is 20mm high and has a diameter of 10mm. Resistance is 1100 ohm. The pins where the wires connect are very fragile. I already killed 3 relays in the process. On eBay I bought 7 for around 9€.

The third picture shows a car relay. I guess it's 24V. It is 16mm high and has a diameter of 15mm. So this doesn't fit.


Which one do you want to use first? Ill add a housing for it to thingiverse files.

Hey. I have tried a 12V relay. It's resistance is 250ohm. I managed to solder everything together and it worked. I used a 3.8V 30mA rainbow LED and manually passed a magnet along the coil. It lit up and showed the first 2 colors. Albeit very dim, it worked. Then I wanted to insert it into the housing and realized I had to desolder again so I could build everything together. And tehn I realized that I soldered the LED to close to the capacitor, so that when I screwed in the 2nd housing containing the coil, the LED head interefed with the thread of the coil housing.

Anyways 12V coil works but I could not test it on my bike and see if it generates more light.

Heh yea there is no other way to put it together then as described in Step 2.