Introduction: Bike Blinkers/ Hazard Lights

These super cool simple to make bike lights work on almost any bike and look great! They last for hours on end and use simple Arduino code to run it. Lets get to building!


  • (20x) 3mm LEDs
  • (2x) NPN Transistors
  • (2x) 35 Ohm Resistors
  • (2x) 100 Ohm Resistors
  • (1x) 9v Battery
  • (1x) 9v Battery Clip
  • (2x) Push Buttons
  • (1x) Power Switch
  • Extra Wire
  • (1x) Arduino Uno

Step 1: Build the Frame (3D Print)

What I have done is drawn up the way the light is going to look using Inventor. You can also use Tinker Cad as well. I will attach the STL files below so you can use which ever slicer you wish and 3D Print it. I recommend 0.15mm for the print quality at a 10% infill to make it print faster. The case it designed to fit an Arduino Uno but if you use a smaller microcontroller (like the Arduino Nano), you. Moreover, the casing for the buttons only fits my type of buttons. You might need to design your own if you are going to use different buttons. Another option is to use a three way switch where you can change the blinker direction with one hand and just hot glue the switch to the handle bars.

Step 2: Assemble the Electronics

What I have done is taken the Lights, hot glued the back of them in place, and connected all of the positive and negative leads together in parallel. What this does is makes it so that the 9v battery can easily power all of the LEDs. I connected all the negatives of both sides and left the positives from each side independent from each other. That way the Arduino can control each half of the lights respective to when you press the button. I then added a resistor to limit the current that way it doesn't damage the LED bulbs. The reason we are using a transistor is to protect the Arduino. If you pull too much current from a pin on the Arduino board, you can potentially damage the Arduino which is not good. It is much safer to use the Arduino to open a transistor like a switch and allow the 9 volt battery to power the LEDs directly. See the pictures above to see how I wired the LEDs together.

Step 3: Assemble the Frame of the Lights

I will be using hot glue to assemble all the pieces since it is easily assessable, holds up well, and has the ability to easily be removed if something needs to be repaired. I glued on the back wing plates to the front plate and let it dry. I followed this up by fishing the wires through the rectangular hole in the Arduino case in order to connect it onto the Arduino. You can either hot glue or tape the Arduino in place using double sided tape. After attaching this piece, I moved onto the bike clips.

Step 4: Assemble the Attachment Clips

Assemble the attachment clip and secure it in place using bolts with a 0.25" diameter. By doing so, you can tighten it to whatever thickness your bike post is. This allows for it to be easily modular to transfer between bikes. You can also attach the back Plate of the Arduino housing to the bike clip assembly using a nut and bolt. Once this is complete you should have two parts, The light assembly and the clip assembly. DO NOT GLUE THESE TOGETHER YET. We need to ensure that the wiring is correct and works. We also need to code the Arduino.

Step 5: Secure the Buttons to the Bike

If you are using buttons like me, you can attach the buttons into the clips and bolt them next to your bike handles. See the picture above. This will allow your handles to easily reach the buttons without making it an inconvenience. String the wires all the way down to the back of the seat where the Arduino will be housed.

Step 6: Plug It All Together

Plug In:

9v + into Vin

9v - into GND


Base of transistor on left side into One of SwitchOne Pins

Base of transistor on right side into One of SwitchTwo Pins

Button (Left) into pins 2 and the Transistor Base

Button (Right) into pins 7 and the Other Transistor Base

Collector pins from both sides to 9v +

Power switch in between 9v+ and everything else connected to it. (Prevents passive loss of battery power)

[Schematic Is in Picture Above]

Step 7: Code the Arduino

I will attach the Arduino Code file Down below. It is very simple. All it does is constantly blink an output from pins 2 and 7. When this happens, it makes it easy for the lights to simultaneously blink. You won't see the blinking until the button is pressed. Then the lights will come to life. When both are pressed, they blink synchronously making the lights give off a hazard light effect. If you want to change the speed at which it blinks, change the delay(x) number.

Step 8: Test and Finish Assembly

When You are testing it, the left button should blink the left side and the right button should blink the right side. If you click them both then both sides should blink simultaneously. If it is all working as it should, hot glue the Two parts together and secure onto the bike. Just Like that, you have made your own Bike Blinkers!

Step 9: Final Thoughts

I really hope you guys enjoyed this project. Make sure to Vote for it and try it out for yourself. If you have any questions or just want to say hi, leave a comment down below and I will make sure to answer. Thanks again, and happy building!

Bikes Challenge

Runner Up in the
Bikes Challenge