multplexing 7 segment leds

hi group,
i have a lumex ldq-m284ri quad seven segment led display and am wonder how
to display separate digits on each segment since they are connected together.
my friend said i need to multiplex it, but he was not sure how to do it.
does anyone have experience on this technique and what to share it.

thank you in advance.

dave

On Wed, 24 Mar 2004 20:38:17 GMT, david <davec@usa.net> wrote:

>hi group,
>i have a lumex ldq-m284ri quad seven segment led display and am wonder how
>to display separate digits on each segment since they are connected together.
>my friend said i need to multiplex it, but he was not sure how to do it.
>does anyone have experience on this technique and what to share it.

Multiplexing the digits means displaying only one digit at a time in
rapid succession so that the eye sees all the digits.  You select a
digit by powering the common pin of a selected digit.  At the same
time you sink to ground the segments that should be on for that digit.
As each digit is selected sequentially, the appropriate segments are
switched to ground.  So even though there is only one set of segment
pins for the entire module, you can still share them among all the
digits in the module.  In short, you need to switch both the high side
and the low side of the LED arrays.


-Robert Scott
 Ypsilanti, Michigan
(Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)

On Wed, 24 Mar 2004 20:38:17 GMT, the renowned david <davec@usa.net>
wrote:

>hi group,
>i have a lumex ldq-m284ri quad seven segment led display and am wonder how
>to display separate digits on each segment since they are connected together.
>my friend said i need to multiplex it, but he was not sure how to do it.
>does anyone have experience on this technique and what to share it.
>
>thank you in advance.
>
>dave

Robert covered the hardware concept. 

In your firmware you can do this: 

1)	Set up a periodic interrupt of something like a few msec. 
	If you have a faster interrupt you can chain off it with a
	divider. 

2)	Set up a global 4-byte array and a counter (a couple of bits)

3)	Each interrupt, use the counter as a pointer into the array 	
	and get	the data for that digit (0..3).  Turn off all 		
	your column drivers. Output the new data to your segment 	
	drivers	(you may wish to 1's complement it) and then turn on 	
	the appropriate digit driver.  advance the counter mod 4 and 	
	you're done with the interrupt. 

Now all you have to do is set up the appropriate pattern of 0's and
1's in the 4-byte array for what you want to display, at your 
leisure. The interrupt routine takes care of displaying it. If you 
had a 4 digit unpacked number to display you'd just use the digits 
in a lookup table to find the segment patterns.

Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

david wrote:
> hi group,
> i have a lumex ldq-m284ri quad seven segment led display and am wonder how
> to display separate digits on each segment since they are connected together.
> my friend said i need to multiplex it, but he was not sure how to do it.
> does anyone have experience on this technique and what to share it.
> 
> thank you in advance.
> 
> dave
> 
please check microchip application notes : do a search with "dot matrix" 
  or "seven segment".

Laurent
www.amontec.com