charlieplexing max per pin

[toprank]

In charlieplexing do you have to spread the LEDs evenly?

example 1:

18 pins = 306 LEDs (would this mean 17 LEDs per pin MAX?)


example 2:

33 pins = 1056 (32 LEDs per pin MAX?)


thanks for your help

 

[3v0]

Every LED is connected to 2 pins. 1 to the cathod 1 to the annode.
All pins but the 2 needed to light a specific LED are tristated.

Given your question I am not sure that you understand charlieplexing.
At max capacity they are evenly distributed, but maybe not as you
expect them to be hooked up.

 

[toprank]

2 IO Ports allows 2 LEDs, LEDs = 2 * ( 2 - 1 )
3 IO Ports allows 6 LEDs, LEDs = 3 * ( 3 - 1 )
5 IO Ports allows 20 LEDs, LEDs = 5 * ( 5 - 1 )
6 IO Ports allows 30 LEDs, LEDs = 6 * ( 6 - 1 )
8 IO Ports allows 56 LEDs, LEDs = 8 * ( 8 - 1 )


is this the correct format?


2 PIN would have 2 LEDs

3 PIN would have 4 LEDs

5 PIN would have 14 LEDs

6 PIN would have 10 LEDs

8 PIN would have 26 LEDs

total LEDs 56
???

 

[3v0]

Yes. Schematics would tell me that you know how to hook them up.

 

[blueroomelectronics]

Problem too is the LED duty cycle gets high rather quickly. Remember only 1 LED is on at any given moment so it'll be hard pressed to be bright with more than 20 LEDs

 

[toprank]

https://www.youtube.com/watch?v=4MGKhFIujM4&feature=related

check this out. What kinda power you think it's using? all the LEDs look bright.

Problem too is the LED duty cycle gets high rather quickly. Remember only 1 LED is on at any given moment so it'll be hard pressed to be bright with more than 20 LEDs

Did you mean trying to light 20 in a fast frame?

 

[rezer]

Here's a link.

**broken link removed**

We've used similar circuits at work using 8 i/o lines for 20 LEDs. I works really well. This sort of resembles a switch matrix you wouul find in a keypad (except with switches of course).

 

[blueroomelectronics]

https://www.youtube.com/watch?v=4MGKhFIujM4&feature=related

check this out. What kinda power you think it's using? all the LEDs look bright.

Did you mean trying to light 20 in a fast frame?

Charlieplexing is a matrix where only one LED is on at a time, so 20LEDs would each have a 1/20 duty. Your 3D array is probably not Charlieplexed but instead multiplexed.

Edit: I noticed a 80LED charlieplexed (no schematic so I couldn't verify) on instructables. Can't really see why you'd want to with a LED cube as its design lends itself better to a standard XYZ matrix.

 

[Pommie]

Charlieplexing is a matrix where only one LED is on at a time, so 20LEDs would each have a 1/20 duty.

I think you'll find that even with charlieplexing you can light n-1 LEDs at any one time. You make 1 pin (edit) high and all the others either (edit) low or tristate. Check Mikes novelty clock. So, with 8 outputs (56 LEDs) you end up with a duty cycle of 12%.

Mike.

 

[toprank]

One thing I am not understanding is if I have to turn on/off all the LEDs within the PIN or would I be able to pick an LED within the PIN to turn on/off?

 

[Pommie]

I just edited my post as I made a stupid typo and so it may make more sense now. With charlieplexing or multiplexing you can turn on any combinations of LEDs. Have you looked at Mike K8LH's clock thread.

Mike.

 

[blueroomelectronics]

Problem with turning on more than one LED at a time is even brightness as you're sharing one resistor for many LEDs.

PS Mike K8LH's clock is not true charlieplexing but more an advanced mux. Charlieplexing uses both forward and reverse biased LEDs (It also doesn't work very well for blue or white LEDs as they still glow with very little current when charlieplexed)

Now a clock with both CC and CA displays might be interesting to see.

 

[Pommie]

Problem with turning on more than one LED at a time is even brightness as you're sharing one resistor for many LEDs.

No, you can give each LED it's own resistor. You can also have 1 resistor on each return leg therefore only needing n resistors. These return resistors would be on the left in Mike's diagram.

PS Mike K8LH's clock is not true charlieplexing but more an advanced mux. Charlieplexing uses both forward and reverse biased LEDs (It also doesn't work very well for blue or white LEDs as they still glow with very little current when charlieplexed)

Look again, if RB0 is high and RB1 is low then one LED lights. RB0 low and RB1 high and a different LED lights. It is true charlieplexing but drawn in a way that clearly shows you can light multiple LEDs at the same time. Note, there are only 42 LEDs shown but if transistors are added for B6 and B7 then the full 56 would be there from 8 outputs. And, if you think the transistors somehow change things just pretend they aren't there and B0 connects straight to column zero etc.

Mike.
Here is Mike's diagram for anyone not familiar with it.

 

[blueroomelectronics]

Ahh I see it now.