How does charlieplexing work ?

[simonwai999]

hi
i found this and read articles about it
still not quite understand how charlieplexing works
hmmmmmm
i don't know if anyone can explain a bit to me
thanks so much

 

[pcup]

charlieplexing 7 segment displays

Charlieplexing is an electronics technique developed by Charlie Allen (hence the name) at Maxim in which relatively few I/O pins on a microcontroller are used to drive a large number of LEDs.

With Charlieplexing, n drive pins can be used to drive n digits with n-1 segments each; in other words, n drive pins can be used to control n2-n LEDs. Traditional multiplexed display technique would take 2n drive pins to control n2 LEDs.

Charlieplexing works by having the I/O pins alternate between driving digits and driving segments.

For example, Charlieplexing can drive a seven-segment display (actually 8 segments when you include the decimal point) of up to 9 digits with 9 I/O pins. Standard multiplexed display techniques would require 17 I/O pins to drive the same display.

Much like standard multiplexed displays, all the cathodes of any particular digit are connected together to a single I/O pin which remains low. Much like standard multiplexed displays, each anode of each LED of a particular digit is tied to the current-limiting resistor of a different I/O pin.

During operation, only one of the I/O pins is pulled low at any one time, pulling the cathodes of one particular digit low, acting like the digit-select line of standard multiplexed displays. All the other I/O pins connected to the display act as the "segment select" "anode pins" of a standard multiplexed display. All those pins are either "enabled" (pulled high through the current-limiting resistor) or "disabled" (aka "left disconnected" or "high Z" or "direction=input").

Any LEDs that has both its cathode (digit) selected and its anode (segment) selected turns on and glows. The other LEDs stay dark at that time.

Some Charlieplexing displays light up all the appropriate segments in a particular digit at the same time, scanning through the digits much like standard multiplexed displays. (They use an internal current source or an external resistor-diode on each I/O pin to keep the LED intensities matched). The "resistor-only" Charlieplexing displays only light up one LED at a time, scanning through each segment of each digit.

Since some of the LEDs will be driven with a reverse-bias voltage when they are not lit, the developer must make sure that the LEDs can withstand the reverse-bias without leaking. Typical red LEDs are rated at only 3V or 5V reverse bias, so try to choose 5V reverse-rated diodes and to run the LED driver at less than 5V. Leaking diodes will show up as ghosting (faint light) in other LEDs, as the leaking diode(s) allow small unwanted currents to flow.

Simple search in Google can solve your problem... atill you are not stisfied
Look at this
Even you want to test our brains we can't extend this thread for jut downloading pints you can have good practical tutorial at **broken link removed**

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Pcup

Oh Sorry i forgot to say that if you want to attach me any technical document related to your request in MB to download with this thread ..?? i can !!! .. But please dont request for Points to Donation for download
.........

 

[simonwai999]

Re: charlieplexing

thx for your detailed reply
regards

 

[nguyennam]

Re: charlieplexing

You can surf in Maxim website, there are documents, parts dedicated to charlieplex.