Introduction: Astable Multivibrating Bicycle Light

This will be made in two main parts, breadboarding and then soldering together a semi permanent circuit. It might work if you want to skip one or the other parts but it's fun to learn how it works and tune it with a schematic and breadboard then put together something you can keep using.

If you just want to try to breadboard and learn about the astable multivibrator there might be more comprehensive Instructables out there which explain more how it works.

See: for a step by step of a breadboard for the circuit we'll be using

and read the Wikipedia mulitvibrator article for some background on the concept of the circuit.

Step 1: Breadboard Your Oscillator

First off we want to breadboard our circuit so you can swap stuff out if you want different timing or want a different power setup than I have. So first off gather the materials.


  • 2 transistors (npn here but pnp can work too) (data sheet)
  • 4 resistors (ohms can vary based on timing and light power requirements). I used two relatively small resistors leading to the LED's (80 ohm leading to purple and 2.75 k ohm leading to the orange, while I swapped out the other LED's with ranges from 30k to 200k ohm to get different blinking speeds.

  • 2 Capacitors ( 2 electrolytic 10 uf ones for this circuit)

  • Battery, anywhere from a watch battery to a 9 volt depending on your LED setup and the tolerance of the components you're using.

  • And a prototype board which is big enough to hold however many leds you want to use and the other components. Or you can just solder all the right things together or use a pcb but, for the first version I recommend a small to medium prototype board.

Then check out the schematic: and try and breadboard it.

Then I like it's a good idea to try and draw your own schematic as you lay out the circuit.

Step 2: Solder All the Compenents Together

You can use any prototype board you can fit all your components on or design a pcb to be milled in a program like Kicad or Eagle and send out to have your board fabricated for you. Or you could solder wires right to the components and still get it to work but it probably won't be the sturdiest circuit.

You can also design a little 3d printed holder for your circuit and power supply plus figure out a way to attach your light to whatever you want it to sit on. I'll share a couple of my versions.

Makerspace Contest 2017

Participated in the
Makerspace Contest 2017

First Time Author Contest

Participated in the
First Time Author Contest