Help - someone who knows leds and eletrics stuff

[Cajun]

Okay need to wire up some LEDS

http://www.dse.co.nz/cgi-bin/dse.storefront/45205e95023e05e4273fc0a87f99068d/Product/View/Z4025
(2.1V 20mA HP HLMP-3850)

Wanna hook these up to a standard 12v source. will either most likley be 2 of these, they most likley be wired up sepeply(on there own ciruirts to power source)
what sorta resister should i be using so these go

Thanks

[bungbung]

If you want 20mA through your LED which is a 2.1V, and your running voltage is 13.8, then the resistor will need to drop 11.7V. V/I=R 11.7/.02=585Ohm. The closest match would be 680Ohm (in the E12 range).

You would be better to get a 560 and a 27 in series, or a 590Ohm from the E24 range.

For a 12V source, the value is 495Ohm, for which 560 will be fine.

For 2 LEDs and one resistor, you'll want a 270Ohm.

[sAsLEX]

What he said!

Although you could make a little circuit up like http://saslex.orcon.net.nz/LED_DRIVE.JPG

[skelstar]

Woo, is that eagle sAsLEX?

[Cajun]

cheers bungbung 560 ohm is what i got for my calcations also, but its been like 4-5 years last time i played with leds.

[andrea]

too bad your in tauranga i could of helped you out with soldering them in, i used to work for f&p electronics

[Cajun]

Nah i know all soldering etc, just been a few years since i done anything, and wanted to make sure my maths was correct.

[sAsLEX]

Woo, is that eagle sAsLEX?

A Hawk?!

It was a dual intesity brake light cicuit running at 100Hz and having a regulated rail.

[skelstar]

The CAD software used to draw the circuit mate.