The real downside that I see is the huge quiescent current, especially with 5V Vdd. Specifically, when each of the inputs associated with a transistor pair is tristated, both transistors are saturated and the quiescent current is about 30 mA. That's about 90 mA for the circuit shown in the Design Idea. dwayne At 01:20 PM 10/16/2008, Bob Blick wrote: >Hi Al, > >20 LEDs off 4 pins, that is sweet! > >Only real limitation is the low voltage requirement, Vled > 1/2 Vcc. >Good reason to go blue :) > >Thanks for posting it. > >Cheerful regards, > >Bob > > >On Thu, 16 Oct 2008 11:35:26 -0700, "Al Shinn" >said: > > I must confess that I did not study the article... > > > http://www.edn.com/article/CA6602447.html?spacedesc=designideas&industryid=44217&nid=2431&rid=1240235916 > > Mutliplexing technique yields a reduced-pin-count LED display - > > 10/16/2008 - EDN -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist