[sdiy] Driving LEDs

[James Patchell]

It might be a little pricey, but I would use a CPLD.  The parts are about 
$3.  The software is free from the Xilinx website.  If all you need to do 
is the decoder, I would use the XC9536.  However, there are are other logic 
jobs to do, consider putting everything into a CPLD.

Other options...

To get 20 lines you need three 74xx138 decoders.  These decoders have 
enough inputs that you will not need any external logic to decode all 
twenty lines from 5 bits (plus a few extra).  Material cost for this is 
about $1.50.  If you use through hole, add $1 for each chip (in labor).


At 09:09 AM 12/22/2003 -0800, John Blacet wrote:
>OK, here's the problem:
>
>I need to drive 20 LEDs from a PIC type uC. The LEDs are on a separate
>board so I want to keep the number of interconnects small. I only need
>one LED at a time to be on. So, I seem to need a decoder with 5 lines in
>to 20 out. Most of the stuff I see is 3 to 8. Any ideas?
>
>--
>Regards,
>--/////--
>John Blacet
>Blacet Research
>http://www.blacet.com
>-------------------------------------------------------------------------------------
>
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         -Jim
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