Jan 302011

This project requires you to be somewhat comfortable with the breadboard and placing components in the proper sequence.

In particular, pay attention to:

  • The negative stripe on the capacitors (should always point to ground)
  • The pins of the transistors (its helpful to know which are E,B, and C)

To build this circuit:

  • 9V battery or power source
  • Transistors (two NPN, we used 2n3904)
  • Capacitors (we used 100uF)
  • LEDs (2)
  • resistors (2 of 10k Ohms)
  • resistors (2 of 470 Ohms)
  • push button switch
  • jumper wires

Alternative breadboard layout for LED flasher:

If you want a simpler layout with less jumper wires, here’s another version we built. It’s the same circuit, but the transistors and capacitors mirror each other so be mindful of polarity!

alternate layout

Video of dual LED flasher in action:

where I test the circuit in Ktechlab before showing the build test

  One Response to “LED Flasher using 2 LEDs and 2 transistors”

  1. Nice example! I have tried ktechlab myself and wonder one thing, since I can’t find this info in the public documentation.

    How do you add capacistors with polarity in ktechlab? I look like your’s have + signs attached to them, but there are only bipolar capasitors available in ktecklab, at least as far as I can tell.

    You also seem to use a standard transistor in your drawing, I can’t find those eiter in ktecklab. Is there some kind of library that I can import to get these.

    Sorry for bothering you with this, but I have tried googling this without results. The best I found was your video.

    Thank a lot, nice demo! =)

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