[sdiy] Driving LEDs

[Don Tillman]

   > Date: Mon, 22 Dec 2003 09:09:26 -0800
   > From: John Blacet <blacet at blacet.com>
   > 
   > 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?

Place the LEDs in a matrix.   Use a 3-to-8 line decoder to drive the
columns positive and a 2-to-4 line decoder to drive the rows negative.
That's 5 bits to connect.

Or any variation of that, optimized to your specific situation.

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com