max number of led displays that could be multiplexed

I've got eight 7-segment displays.  I know I've multiplex four at once but
eight seems like a lot.  It'd be slick to need just 16 pins.  Can it be
done?	   
					
---------------------------------------		
Posted through http://www.EmbeddedRelated.com

On 2010-01-29, Joel <joelbenway@n_o_s_p_a_m.gmail.com> wrote:

> I've got eight 7-segment displays.  I know I've multiplex four
> at once but eight seems like a lot.  It'd be slick to need
> just 16 pins.  Can it be done?  

Yes.

-- 
Grant Edwards                   grante             Yow! An Italian is COMBING
                                  at               his hair in suburban DES
                               visi.com            MOINES!

On Fri, 29 Jan 2010 07:32:12 -0600 "Joel"
<joelbenway@n_o_s_p_a_m.gmail.com> wrote in Message id:
<97udndywFsvBfv_WnZ2dnUVZ_u2dnZ2d@giganews.com>:

>I've got eight 7-segment displays.  I know I've multiplex four at once but
>eight seems like a lot.  It'd be slick to need just 16 pins.  Can it be
>done?	   

Of course. Here's one for 16 digits:
http://www.maxim-ic.com/app-notes/index.mvp/id/3210

>On Fri, 29 Jan 2010 07:32:12 -0600 "Joel"
><joelbenway@n_o_s_p_a_m.gmail.com> wrote in Message id:
><97udndywFsvBfv_WnZ2dnUVZ_u2dnZ2d@giganews.com>:
>
>>I've got eight 7-segment displays.  I know I've multiplex four at once
but
>>eight seems like a lot.  It'd be slick to need just 16 pins.  Can it be
>>done?	   
>
>Of course. Here's one for 16 digits:
>http://www.maxim-ic.com/app-notes/index.mvp/id/3210
>

If you are looking for dedicated hardware also look at the ICM7218. It w2as
made by both Intersil and Maxim, but today...

If you are trying to do this as a roll your own- look up "charlieplexing"
on the Maxim web site and also EDN and Electronic Design. There was a
flurry of discussions recently and how to use the least number of bits.

I have a very old HP application book on optoelectronics (in electronic
format) that discusses this quite well. if you let me have an address, I
can try and figure out how to get the 120MB  to you.

-Aubrey	   
					
---------------------------------------		
Posted through http://www.EmbeddedRelated.com

>>On Fri, 29 Jan 2010 07:32:12 -0600 "Joel"
>><joelbenway@n_o_s_p_a_m.gmail.com> wrote in Message id:
>><97udndywFsvBfv_WnZ2dnUVZ_u2dnZ2d@giganews.com>:
>>
>>>I've got eight 7-segment displays.  I know I've multiplex four at once
>but
>>>eight seems like a lot.  It'd be slick to need just 16 pins.  Can it be
>>>done?	   
>>
>>Of course. Here's one for 16 digits:
>>http://www.maxim-ic.com/app-notes/index.mvp/id/3210
>>
>
>If you are looking for dedicated hardware also look at the ICM7218. It
w2as
>made by both Intersil and Maxim, but today...
>
>If you are trying to do this as a roll your own- look up "charlieplexing"
>on the Maxim web site and also EDN and Electronic Design. There was a
>flurry of discussions recently and how to use the least number of bits.
>
>I have a very old HP application book on optoelectronics (in electronic
>format) that discusses this quite well. if you let me have an address, I
>can try and figure out how to get the 120MB  to you.
>
>-Aubrey

You may want to check AN1216 and Application Brief D-0004 from Avago.

-Aubrey	   
>					
>---------------------------------------		
>Posted through http://www.EmbeddedRelated.com
>	   
					
---------------------------------------		
Posted through http://www.EmbeddedRelated.com

Joel wrote:
> I've got eight 7-segment displays.  I know I've multiplex four at once but
> eight seems like a lot.  It'd be slick to need just 16 pins.  Can it be
> done?	   
> 					
> ---------------------------------------		
> Posted through http://www.EmbeddedRelated.com

pay attention to the peak current specs on the leds and
whatever you're using to drive 'em vs. the peak current needed
to get the brightness you want.

Joel wrote:
> I've got eight 7-segment displays.  I know I've multiplex four at once but
> eight seems like a lot.  It'd be slick to need just 16 pins.  Can it be
> done?	   

Depends on what sort of intensity/brightness you want from them.

8-way mux was commonplace many years ago to economize on
hardware.  Often, the display multiplexing hardware
was tied to the *keyboard* multiplexing (e.g., drive a
display digit and a keyboard column at the same time).

Look at the efficiency of your displays (i.e., how little
current does it take to get the brightness you want) and
the maximum current each digit can tolerate (before it becomes
a DED -- Darkness Emitting Diode).