Thanks alot for the help and time, guys. I have save the info in my folder for future reference. Have a nice day. cheers, Davis Jinx wrote: > best rgds, > Davis In addition to Bob Ammerman's reply, to put the resistance in a formula R = (E-Vf) x 1000/I Where R=ohms, E=supply, Vf=LED forward voltage, I=LED current in mA To use Bob's example R = (12-2.1) x 1000/25 = 396. You should get good brightness with most LEDs using more than 390, say 1k8 (=5.5mA). Driving a red/yellow/green with a PIC pin would be fine in most cases with 1k This applies to DC supply. There are times, say when using a regulator that you don't want to load any more than necessary, when you'd rather put the LED on the AC from the transformer. What you do is put a small diode (like a 1N914) in reverse parallel to the LED and use half the resistance that you would have done had it been a DC voltage You can also put an LED acrross the mains, but I think it's frowned on, by adding a 220nF X2 rated capacitor in series (R and the reverse parallel diode are there too) to limit the current Another usage is with pulsing drive, such as moving signs and infra-red transmitters. In these cases you calculate the average amperage. This is related to the duty cycle of the wave (as per AC). For example, an infra-red transmitter LED may have just 1 or 2 ohms in series, because it is being driven with pulses that can be measured in microseconds at a fairly low duty cycle. IOW, roughly, if the duty cycle is 1:99 (the LED is on for only 1% of the time), the resistor is reduced accordingly. During the 'on' time, the LED may be passing several amps, but it is for such short duration that it doesn't cause destructive heating. This information should be included in the LED's datasheet -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics --------------------------------- Do you Yahoo!? Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics