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20 Jan 2012

 atoomnet.net writes:

Try making a double led dice with 14 leds driven only by 4 available pins of an Atmel Attiny13a. I did it, and it worked:

14 leds can be driven by a technique called charlieplexing when not many microcontroller pins are available. This technique works from the fact that leds are diodes and that those diodes have a little voltage drop. In the network of leds, you can make one led turn on by applying a voltage smaller than twice the voltage drop of a led. In this way, only one led lights up. The other leds do not turn on because the voltage is not high enough.

To make all the leds light up you must cycle through all the leds very fast. Only one led can be turned on at a time. If you cycle through all leds very fast they all seem to be on at the same time to the human eye.

Charlieplexed double led dice - [Link]

 

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