Wiblocks --- FAQ

Question

How many LEDs can I connect directly to the microcontroller output pins?

Answer

Using Charlie-plexing you can configure N lines to control N*(N-1) LEDs.

Charlie-plexing uses the three states of microcontroller pins to enable a large number of LEDs to be controlled. An LED is turned on by configuring two lines as outputs and setting the LED anode high (Vcc) and the cathode low (GND). An LED is turned off by setting either the anode or cathode to a high impedance state (tri-state).

It is easy to see the LED operation by arranging the LEDs in a matrix. For each output pin an LED row is created. For each row columns are created using all the other output pins. To turn an LED on the anode needs to be set high and the cathode needs to be set low. This corresponds to setting the row input low and the column input high.

The schematics shown are simplified and may require additional ballast resistors or current drive circuitry.

Limitations

Number of PinsNumber of LEDs
36
412
520
630
742
856
972
1090
11110
12132
13156
14182
15210
16240
17272
18306

References

Lancaster, Don (2001) Tech Musings, August, 2001 Retrieved May 2, 2010

wikipedia Charlie-plexing