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### Topic: Charliplexing Code without Library (Read 2035 times)previous topic - next topic

#### MonorailOrange

##### Nov 08, 2012, 10:51 pm
Hi Team,
I am working on learning how to charlieplex to build homemade displays (next, I'll work on using MAX7219's, but charlieplexing seems simpler to start with). I have built my first matrix, a simple 3x3 square. I am controlling 9 LED's with 6 pins, the columns are the anodes and the rows are the cathodes. I can't seem to control the device. I can test each individual pin by connecting the respective column to pin 13, and the row to GND and running blink. However, when I try to control them using code, nothing happens. I have a simple code here that was intended to simply flash the top left LED, but nothing happens. Can you help me figure out why?
Code: [Select]
`int Col3 = 13;int Col2 = 11;int Col1 = 10;int Row3 = 3;int Row2 = 5;int Row1 = 7;void setup(){  pinMode(Col3, OUTPUT);  pinMode(Col2, OUTPUT);  pinMode(Col1, OUTPUT);  pinMode(Row3, INPUT);  pinMode(Row2, INPUT);  pinMode(Row1, INPUT);}void loop(){  digitalWrite(Col1, HIGH);  digitalWrite(Row1, LOW);  delay(500);  digitalWrite(Col1, LOW);  delay(500);}`

Thank you guys!
MonorailOrange

#### AWOL

#1
##### Nov 08, 2012, 10:58 pmLast Edit: Nov 08, 2012, 11:00 pm by AWOL Reason: 1
Quote
the columns are the anodes and the rows are the cathodes.

I think you may not understand how charlieplexing works, or how the diodes are wired.
Diodes are wired in opposing pairs across all combinations of pins.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

#### fungus

#2
##### Nov 08, 2012, 11:01 pmLast Edit: Nov 08, 2012, 11:03 pm by fungus Reason: 1
All pins should be outputs...

But:
a) That's not how charlieplexing works
b) Trying to light rows of LEDs from an Arduino pin is a bad idea. Too much current will kill it (the Arduino pin).

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### nickgammon

#3
##### Nov 09, 2012, 12:51 am

It isn't, believe me. The code is quite complex compared to the MAX7219, and you still have to address the issue of current-limiting resistors.

Here's a post about the MAX7219:

http://www.gammon.com.au/forum/?id=11516
Please post technical questions on the forum, not by personal message. Thanks!

#### nickgammon

#4
##### Nov 09, 2012, 12:51 am
The MAX7219 has built-in current limiting, which makes life easier.
Please post technical questions on the forum, not by personal message. Thanks!

#### MonorailOrange

#5
##### Nov 09, 2012, 01:04 am
So would it be better for me to learn charlieplexing using something like the LoL Shield? I have ordered an 8x8 MAX7219 board, but it's going to take forever to get here (IF it ever gets here).

#### nickgammon

#6
##### Nov 09, 2012, 01:35 am
OK. Let's assume you have a resistor in series. I hope you do. Then this works:

Code: [Select]
`const int Col3 = 13;const int Col2 = 11;const int Col1 = 10;const int Row3 = 3;const int Row2 = 5;const int Row1 = 7;void setup(){  pinMode(Col3, OUTPUT);  pinMode(Col2, OUTPUT);  pinMode(Col1, OUTPUT);  pinMode(Row3, OUTPUT);  pinMode(Row2, OUTPUT);  pinMode(Row1, OUTPUT);}void loop(){  digitalWrite(Col1, HIGH);  digitalWrite(Row1, LOW);  delay(500);  digitalWrite(Col1, LOW);  delay(500);}`

Note that they all have to be outputs otherwise there is nothing to sink the current.

Charliplexing works with a combination of output/high output/low and input (high impedance).

As I recall you make a column output/high and the rows output/low, and the other columns input, to make a particular junction light up. Or reverse the low/high to make the other LED (wired the other way around) to light up.
Please post technical questions on the forum, not by personal message. Thanks!

#### fungus

#7
##### Nov 09, 2012, 10:21 am

So would it be better for me to learn charlieplexing using something like the LoL Shield? I have ordered an 8x8 MAX7219 board, but it's going to take forever to get here (IF it ever gets here).

??

Where did you order it? You can buy a dozen MAX7219s on eBay for \$10 and have them in a week.

I agree with Nick, a MAX7219 is FAR easier to work with than charlieplexing and does exactly what you seem to want.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### tmd3

#8
##### Nov 10, 2012, 05:11 am

So would it be better for me to learn charlieplexing using something like the LoL Shield?

It would be better to learn charlieplexing by understanding its underlying principles.

Based on what you say in your posts, you seem to be confusing a charlieplexed array with an LED matrix.  Maybe a matrix was what you intended to use?

In a matrix arrangement, the canonical method is to drive a column pin to its active state, leaving all the other column pins inactive, and then drive the row pins of the LEDs you intend to light to their active state, illuminating some of the LEDs in a single column simultaneously.  Naturally, the roles of the rows and columns can be exchanged, and maybe you want to illuminate only one LED at a time - if one of those is what you want to do, then your code just needs to reflect it.

In a charliplexed arrangement, only one LED is illuminated at a time.  The pin connected to that LED's anode is driven high, the pin connected to its anode is driven low, and all of the other pins are configured as inputs.  The wiring is a lot more complex than a a matrix scheme - and, for all but a few trivial applications, the code is a whole lot more complex - and there's often not a natural one-to-one correspondence between a particular LED's location in the display and the pins that activate it.  But, it'll address more LEDs than a matrix arrangement with the same number of pins.

The explanation of how charlieplexing works is long and complicated; I'm not inclined to reproduce it here, since I'm not entirely sure that charlieplexing is what you intended, and it's already described in many places on the Internet.  I'll suggest the Wikipedia article on charlieplexing, and the resources that it references.  There are oodles of descriptions of LED matrix arrangements on the web; google away.

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