Charlie-plexing

[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]

I can power pin 1:


I can power pin 4:


But I can't do the same thing at the same time, two unwanted LEDs come on:

Edit: I just noticed I missed another unwanted LED between pins 4 and 2.

I'll probably use a dedicated 18F24K22 running at 64MHz to manage the LEDs. I have to test, but blinking each LED individually might give enough persistence of vision (50 Hz or so).

I was initially planning on powering all LEDs active on one pin, but that might complicate things beyond my limitted abilities. I like to keep things simple.

I might also manage a simple keypad, not sure yet. I have enough pins, but tests will show how much the PIC can manage and still give satisfactory visual effects.

Robert

[Demon]

As I sit down to think how to manage this, one MAJOR drawback:

You had better not forget any LEDs on your project 'cause adding one later is going to be "troublesome".

You can always add it at the bottom of your truth table, but I'm the obsessive compulsive type that likes symetry; LEDs are handled in the logic as they are placed on the circuit board. Remnants of hating spaghetti code on mainframes (COBOL + GOTO = NIGHTMARES).

Robert

[Demon]

Some neat stuff I forgot that I found several years ago on Charlie-plexing.

clear
define osc4
cmcon0=7
ansel=0
adcon0 = 0
@ device mclr_off
@ device wdt_off
@ device bod_off
@ device cpd_off
@ device protect_off

led var byte
ledstates var byte
trisstate var byte
delay var word
noghost var byte
gpnoghost var byte

noghost= %111111
delay= 1500

starthere:
gpio.3 = 0
if gpio.3 = 1 then
  goto main
endif
goto starthere

main:
for led = 1 to 6
  select case led
    case 0 : ledstates =%001 : trisstate =%100
    case 1 : ledstates =%010 : trisstate =%100
    case 2 : ledstates =%001 : trisstate =%010
    case 3 : ledstates =%100 : trisstate =%010
    case 4 : ledstates =%100 : trisstate =%010
    case 5 : ledstates =%010 : trisstate =%001
    case 6 : ledstates =%100 : trisstate =%001
  end select
  trisio = noghost
  gpio = ( gpio & %111000) | ledstates
  trisio = (trisio & %111000) | trisstate
  pause delay
next led

for led = 1 to 5
  select case led
    case 1 : ledstates =%000001: trisstate =%101110
    case 2 : ledstates =%011000: trisstate =%101110
    case 3 : ledstates =%000010: trisstate =%101101
    case 4 : ledstates =%010000: trisstate =%101101
    case 5 : ledstates =%000010: trisstate =%011101
  end select
  trisio = noghost
  gpio = ( gpio & %111000) | ledstates
  trisio = (trisio & %111000) | trisstate
  pause delay
next led

trisio=noghost
gpio=gpnoghost

goto starthere
end

Editted to add some colour, original was black on light gray background.

I wish I could give a link and credit, but I can't find anything on google for this now (been looking for over an hour).

Robert

[AvionicsMaster1]

Did this a while ago. Don't know if it will help. http://www.picbasic.co.uk/forum/showthread.php?t=14220

If you use the above program you'll need to change you define osc line.

Good luck.

[Boater]

Hi Demon and AvionicsMaster1
Thank you for the information.
I will try your suggestions though I think typing OR seems the easiest.
Regards
Jim

[richard]

I will try your suggestions though I think typing OR seems the easiest.

Though it looks cool to use those symbols I think it's easier just to type OR and know what it means

.


NOT sure about that , this is what the book says

3.4.2 Logical vs. Bitwise

Logical operators are very different than bitwise operators! There are

circumstances under which PBP will allow the use of logical operators in
expressions. This means that no error message will be generated when you
mistakenly use a logical operator in a bitwise calculation. Consider the following:
result = PORTB AND %00001111
' Returns logical result (1 or 0)
The above example will compile and give a result. The value of the result can only
be one or zero (true or false). If the intent is to use a bitwise operation to obtain a
binary result, you MUST USE BITWISE OPERATORS:

   i_term=0
   d_err=4
   i_err= 3 
   i_term= i_err |  d_err
   serout2 PORTA.0,84,[ "3 | 4 ",9,#i_term, 13,10]
   i_term= i_err OR d_err
   serout2 PORTA.0,84,[ "3 OR 4 ",9,#i_term, 13,10]

PRINTOUT:
3 | 4 7
3 OR 4 65535

[Boater]

Hi Richard
Looking at the PBP3 Compiler Manual it only shows OR as the description for
| in the Bitwise operators. It does show OR as an operator in the Logical operators.

Regards
Jim

[richard]

Logical operators are not bitwise operators
| does a bitwise OR
OR does a Logical OR

2 | 3 = 7
2 OR 3 = ! 0 [ not nothing ]

[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

[AvionicsMaster1]

Depending on the keyboard the | character doesn't look like it on your keyboard. Never could figure out why they do this but it's above the ENTER key and is accessed by using SHIFT and the \ key. It looks like a vertical line separated by a space in the middle. I thought in old programming terminology it's called the pipe symbol.

Though it looks cool to use those symbols I think it's easier just to type OR and know what it means.