Introduction to Electronics for Raspberry Pi: Flashing LED
The Raspberry Pi allows you to build hardware projects to interact with the real world but to do this you need to know electronics. This video shows how to use a 555 timer chip and a few other cheap components to make an LED flash. What has this to do with the Raspberry Pi? Not only do you learn about chips, capacitors, LEDs and resistors in this tutorial but also how to generate a timed digital output - handy for all sorts of Pi projects.
9v battery and clip
220 Ohm resistor (for LED)
4.7k resistor (for pins 6/7)
200-4.7 resistor (to control speed of flashing)
(all these parts are included in the bitsbox.co.uk electronics starter kit)
Also mentioned: Electrodroid."