Charlie-plexing

[Amoque]

As I study what is clearly an amazing example, many thoughts come to mind...

"There is only one step from the sublime to the ridiculous." - Napoleon Bonaparte.

Stay tuned for Robert's forthcoming book: "Burglary with a Light Show"

A subtitle: Redundancy in redundant lighting systems .

While I jest, I do so in fun. I am... I search for an adjective... somehow "flabbergasted" seems appropriate. You are controlling nearly what could be, an entire string of holiday lights, with 10 pins!

Thanks for sharing!

[towlerg]

And the real beauty is that unlike multiplexing you don't have to constantly service the array just set the inputs and outputs and write once to the outputs. Good example Demon.

George

[Demon]

Congratulate me once I get mine working. LOL

Robert

[Charlie]

Hi Robert - a couple questions / thoughts....
I think you have too many resistors. With the original Charlie-plexing, there should be one current limiter per pin, not per diode, since some combinations rely on the forward volt drop of a diode to keep two others from coming on. I think what you did will work, but once you get beyond 3 pins, you may start having different intensities of LEDs. It would certainly save you some components to go per pin rather than per LED pair.
Do the red and green diodes have the same volt drop? Green is usually about double red, so there will be still more challenges. Is it your intent that something is green or red, but never off unless broken? I think that might be difficult to do too. The array will need to be constantly scanned if more than one led should be on at any given time. But you'll want to do that to save power, anyway.
Have you done a big truth table to see what happens for each combination? You'll need that to write the code anyway, but it might save you a lot of work. I don't think this is something that can be tested in a simulator easily since it depends on analogue effects.
Anyway, very cool approach if you can work around those limitations!

[Demon]

Charlie! We were just talking about you.

Hi Robert - a couple questions / thoughts....
I think you have too many resistors. With the original Charlie-plexing, there should be one current limiter per pin, not per diode, since some combinations rely on the forward volt drop of a diode to keep two others from coming on. I think what you did will work, but once you get beyond 3 pins, you may start having different intensities of LEDs. It would certainly save you some components to go per pin rather than per LED pair.

Many LEDs on the same pin may be on, but only a single LED per pair can be lit.

The tri-state properties of a pin control which LED is lit, not forward voltage drop. See Tip #2 in the Microchip PDF.

LED intensity is not supposed to vary depending on active LEDs.

Do the red and green diodes have the same volt drop? Green is usually about double red, so there will be still more challenges.

Probably not, the LEDs I have in stock do not have identical properties. But they are close enough for personal use. I am compensating by using different light intensities; ie: I have varying intensities of LEDs for the same colour. Bulk purchases so I don't have specs.

Is it your intent that something is green or red, but never off unless broken? I think that might be difficult to do too.

I don't understand.

The array will need to be constantly scanned if more than one led should be on at any given time. But you'll want to do that to save power, anyway.

Yes, definitely scanning to save current.

Have you done a big truth table to see what happens for each combination? You'll need that to write the code anyway, but it might save you a lot of work.

Next on my TO-DO list.

I don't think this is something that can be tested in a simulator easily since it depends on analogue effects.
Anyway, very cool approach if you can work around those limitations!

Yes it can be tested, this is digital only. But I don't have Proteus.

Robert

[towlerg]

Here one I made earlier

Actually simulated, it's the display of a tidal state indicator that one day I'll get round to building. The Xylon effect is just to test all bits with the two elements separate.

George

N2 does work, just a slightly dodgy GIF

[Demon]

...Actually simulated, it's the display of a tidal state indicator that one day I'll get round to building. The Xylon effect is just to test all bits with the two elements separate.

George

Either you messed up recording your GIF, or there's a bug in the top row.

And it's Cylon.

Robert



EDIT: It might also be an Internet Explorer thing, I'm still on XP on my laptop.

[Demon]

Charlie, about the red-or-green-or-broken question. I can light the red, green or nothing at all if I wish (which is possible in this application).

I am powering only one pin at a time. Due to the interconnections on the matrix, applying power to more than one pin will have undesired results.

Pass 1:
"1" on pin 1, "0" on pin 2, Input remaining pins lights the top left red LED.

Pass 2:
"1" on pin 4, "0" on pin 3, Input remaining pins lights the top green LED between pins 3 and 4.

But...

Pass 3:
"1" on pin 1, "0" on pin 2,
"1" on pin 4, "0" on pin 3, Input remaining pins lights the top left red LED and the top green LED between pins 3 and 4,
but it also lights
a red LED between pins 1 and 3 and
a green LED between pins 4 and 2
since those circuits are also completed unintentionally.

Robert

[Boater]

Hi Richard
Thank you for the information, seems I have a lot to learn.
I have been reading up on Bitwise in the PBP Compiler Ref manual.
Can't find out how to type in the OR operator, doesn't appear to be on my keyboard.
Anyway I'll keep on reading and see if I can make sense of it.
Regards
Jim

[Demon]

Jim,

If you can't type | using SHIFT, go through again with ALT.

Edit: or come here and COPY the character and then PASTE it in your code.

Robert

[Demon]

Hi Robert - a couple questions / thoughts....
I think you have too many resistors. With the original Charlie-plexing, there should be one current limiter per pin, not per diode, since some combinations rely on the forward volt drop of a diode to keep two others from coming on. I think what you did will work, but once you get beyond 3 pins, you may start having different intensities of LEDs. It would certainly save you some components to go per pin rather than per LED pair.
...

Aaaaaaaand I think this just came back to bite me. LOL

Robert

[Charlie]

Hi Robert,
This article explains what I was trying to tell you about analog vs digital effects: http://www.instructables.com/id/Char...s--The-theory/
The Microchip article is a quick example, but not true Charlie-plexing, and it doesn't scale up nicely.

[Demon]

Ah perception, what a wonderful thing. When I said digital I meant the logic, and when you said analog you meant the properties of the LED. LOL

I had found that article on google but didn't see anything new at first glance and moved on. It's really a few pages deep that it gets into the meat of the matter. Excellent article though, explained everything so clearly.

I especially appreciate how he discusses making a pin input disables it. I never understood "high impedance state". It's simple, it impedes, like that 10M resistor he has on his schematic of the input pin.

It also explains why I couldn't get a decent reading on my Saleae probe; current DOES flow through the unwanted LEDs. It's just that they don't get enough current to light up; hence the importance of forward voltage drop you mentionned (he explains that clearly). It's nice understanding what's going on.

No ghosting with 200usec delay:


No pauses:


Robert

[Boater]

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[Boater]

It seems I went off Topic?

[Boater]

Hi Richard
Thanks again for some great information.
Got the 20 Leds working fine. Tried the pauseus 1200 in the code and they are very dim with 100 ohm resistors.
Found out that in the tris values where you have a pair you leave both alone if the port.4 (16) is involved.
I have been looking through the PBP compiler manual but can not find any reference to the $e0 or the $f0.
Does the $e0 remove the mask from all the upper 4 bits? and are there any more masking commands?
I am thinking of doing a 30 led charlieplex, I have the layout for it.
They are just on a breadboard at the moment and until I can design a good pattern that is where they will stay.
I would like to know more about your last code set but I think I will need to wait until I upgrade and get a 16f1825 pic.
Regards
Jim

[richard]

$e0 = binary 11100000
$f0 = bin 11110000

logical function AND (&) goes like this

a b a&b
0 0 0
0 1 0
1 0 0
1 1 1

logical bitwise function OR (|) goes like this
a b a&b
0 0 0
0 1 1
1 0 1
1 1 1

masking clearing and setting bit/s in a var can be accomplished this way

eg if a = %11111111 (255 or $ff)

then a&$e0= %11100000

then a | 12 = %11101100

see bitwise in book