I want to have an on/off indicator LED on my stealth-mounted radar detector. I just want to indicate when the 12v power supply is there or when it is not there for the radar detector (I control it with a switch).

I have a bunch of old radio shack LEDs in various colors sitting here. I'd like to use one of them.

I know it's been asked on the BBS before, now it's my turn... I don't think I can plug these LEDs directly into the 12v line, can I? What do I have to do to make them work and not burn out too quickly? Just resistors? If so, what value and how would they be wired?

Please Refer To This FAQ for your answers.

http://www.pioneernet.net/optoeng/LED_FAQ.html

I've always wanted to do that, to you.

Heh, touche'.

Actually I found my answer with a search here on the BBS: A 1k ohm resistor in series with the LED is all I needed.

Thanks!

Hi!

You only need a resistor inline with the LED. Here's how to find the value:

Normal Leds drop something like 1.2 V and require 20 mA for full intensity.

You substract 12V-1.2 = 10.8 V that you have to drop at the resistor. R=V/I, so 10.8 V / 20 mA = 540 ohm somthing near that is 510 ohm, or better 560, which will let less current flow through the led, so longer longevity... 10.8V / 560 = 19 mA

As for power of the resistor P = V * I, 10.8 * 19 mA .2 W, a 1/4 W will be fine

So, the result is:

a 560ohm 1/4 W

Included is a picture of such a resistor (for color code: Green Blue Brown and size)

But any value from 500ohm-1kohm would be fine too... same size

And don't forget that leds have polarity, the flat side of the led (viewed from top) goes to the negative:




Hope this helps


Patrick

Hey, cool! An(other?) elctronics technician has joined up. And another Patrick no less.
How long have you been lurking/posting for? Great to see you here.

Hi!

It's been a while, almost two years, but just got my first empeg last year...

I'm not posting often (still a stranger), but I'm reading the BBS everyday.

I just finished school 3 yeras ago and I currently work with PLCs and motors, etc, in a factory here...

An(other?) elctronics technician has joined up.

Patrick is the dude who released the original lyrics scroller before Tony decided to take up on the project. So he's not that new I guess, and certainly already contributed a great deal.
I too, don't have many posts, but rarely miss a post. Only recently my posting habits changed a bit. I wonder how many silent readers are out there.

Judging by the number of anonymous users under 'Who's Online', quite a few!