How long... LED on time without resistors?

**Heckler** · - 14th March 2011, 15:59

Thanks to everyone who replied...

The project is a very NON-Critical Boy Scout electronics merit badge project. I know I need to teach proper LED current limiting to the Scouts (and I will), as well as OHM's law, capacitors, inductors, transistors, resistors, etc. (oh yea, and Software concepts)

In this case due to time limitations and dollar limits on project costs... I am trying to keep the project as simple as possible. They need to be exposed to soldering and basic electronics. I want to "wet" their appetite for programmable microcontrollers. The kit will be an 8x8 LED matrix with a PIC 2-AA batteries and that's it. It will end up being a neckerchief slide that scrolls a scouting message. I may include two pushbuttons to include a simple game.

Similar to these excellent projects...

http://www.instructables.com/id/Mini...-with-built-i/

http://tinkerlog.com/howto/64pixels/

**ardhuru** · - 14th March 2011, 16:22

Along with the other parameters you listed that would matter, its also important *how much time the LEDs stay off* between their 1.5 ms on state; the time they get to catch their breath, so to say. As long as this duty cycle is small enough the design should work fine even at 5 volts. I say this on the basis of a 4 digit 7 segment display I have integrated in a product; no resistors, running 22X7 the past 8 odd years, and no failures...yet.

Regards,

Anand