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--- glossary:glossary_c [2022/03/24 20:40] – [Current] fix link chrisridd
+++ glossary:glossary_c [2022/06/27 12:23] (current) – Removed scaling so GIF will animate. WhiteCF
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 ===== Charlieplexing =====
-Charlieplexing is a method of multiplexing a few I/O ports out of a microcontroller to control a large number of LEDs. It is common for an I/O port to either provide (source) current or provide a low level (sink) from another source of current applied to an LED, to allow an LED to light.  Occasionally when designing a microprocessor circuit that has LEDs, a designer finds there are more LEDs than available I/O pins to control them.
+This is a method of multiplexing a few I/O pins of a microcontroller to control a large number of LEDs. It uses I/O pins that can be 3 state, either source or sink current or be open circuit (switched as input). LEDs are wired in reversed pairs. The LEDs are driven in a multiplexed way, rapidly by software. Only 1 LED is lit at any given time. 3 pins can drive 6 LEDs, 4 pins drive 12 LEDs, 5 pins drive 20 LEDs... See the MERG Journal [[https://merg.org.uk/merg_journal/download.php?fileid=35|March 2006]] p34 for additional information.
+{{:glossary:charlieplexing_slowed.gif|charlieplex}}
-Charlieplexing differs from the common one-port-controls-one-LED scheme by allowing each port to alternately source current or sink current. Charlieplexing takes advantage of the dual use of the I/O port combined with a special LED configuration. The scheme modulates the I/O ports quickly such that the desired individual LEDs appear on. Depending on how the pin wiring and LEDs are arranged, a smaller number of microprocessor pins can control a much larger number of LEDs.  See the MERG newsletter (now called a Journal) of [[https://merg.org.uk/merg_journal/download.php?fileid=35|March 2006]] pages 34 and 35 on the web site for additional information.
 ===== Circuit =====