At 11:51 PM 1/7/00 +1100, Paul wrote: >Mark Willis wrote: > > > 3 resistors? I've tried to fit that, 4 is the only number I come up > > with > > What it the objective? Minimum resistors? Maximum drive current? > > This circuit, or the general task of multiplexing nÓ-n LEDs on n I/O >lines really is my "pet" - I think you'll recall references to it in the >past. A sub-set of the problem is multiplexing 7-segment displays. > > The "optimal" solution involves using one resistor and one SMD NPN >transistor per I/O line. Was it Mark who had a finger in this one? >Collector goes to *un*regulated +ve supply, resistor between base and >emitter, base driven by PIC I/O and emitter to LED matrix. What's wrong with using a CD4511 or 74LS47 decoder? Is the object here to avoid using ICs other than the PIC? ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causae scire" ================================================================