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Easy Electronic Circuit - Two Flashing LEDs

Sunday, 1 April 12, 11:06 am
When a couple of colleagues got Arduinos, I finally got round to getting hold of a starter kit off ebay. It's a very simple kit, with a breadboard and a selection of components that include resistors, capacitors, LEDs and transistors. It also had a couple of circuits pinched off the web to get you started, and they seemed as good a place as any to get started.

With the first one, two LEDs blink on/off alternately. The circuit comprises the following components:
  • LED x 2
  • Transistor x 2
  • 10µF Capacitor x 2
  • 470Ω Resistor x 2
  • 10kΩ Resistor x 2
  • Standard 9v Battery
These components are laid out as in the following circuit diagram:

What's Going On?

The alternating effect must be produced by the transistors being switched on / off by the capacitors discharging and charging. Each transistor can switch the LED on or off, converting the smooth exponentially discharging output from its capacitor into high or low once a threshold is reached.
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/xkcd/ The Simpsons

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