Re: [EE]: Using ULN2803 by Dale Botkin .

On Sat, 23 Jun 2001, Dan Michaels wrote: > Dale.B wrote: > ..... > The LEDs are driven via row/column > >transistors with no current limiting resistors (reduced parts count) > ...... > > Dale, do you really think this is safe? Yep, sure do. Otherwise I wouldn't have designed it that way. There actually is some current limiting provided by the transistors, of course. Since the LEDs are only on for a few milliseconds at most, The average current is still well within a reasonable range. The LED array scanning is interrupt driven using TMR0, and the watchdog is set to prevent any unfortunate results should the software glitch. The maximum duty cycle of the LEDs in my case is 1/33 (or roughly 3%). So, yes, I think it's safe. It was difficult to come up with another way to drive a large-ish array of LEDs with acceptable brightness, and without a lot of power dissipation somewhere... the variable brightness was just a bonus. Dale -- A train stops at a train station. A bus stops at a bus station. On my desk I have a workstation... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.