Any 12VDC Electronic Gurus in 'da hizouse?

**rxrep** · 12-11-2008 03:37 PM

I want to somehow have LED dim when headlights are turned on. Is there any type of relay or anything that would trip when the 12V hits the low beams and then dims the LED (not off, but dim). And when the lows are switched off, the LED go back to bright running lights?

**orangelmo** · 12-11-2008 03:40 PM

Maybe you'd have to have it go through a voltage regulator or something after the relay. Less voltage = dim LEDs. Just a thought not even sure it would work

**rxrep** · 12-11-2008 03:45 PM

That's kind of what I'm thinking, but I wouldn't know where to source parts like that, or exactly what I'd need.

**actlsub9** · 12-11-2008 03:54 PM

Instead of a relay, it would probably be easier to run two separate power sources to the headlight and switch between the two. You may want to look more into LED dimming as well. It is not as straightforward as other lights.

**rxrep** · 12-11-2008 03:59 PM

Yeah, was hoping it'd be something simple. Thanks, Greg.

**coowhip** · 12-11-2008 05:35 PM

Pulse Width Modulation
A far superior method of dimming LEDs is to use Pulse Width Modulation (PWM). With PWM strings of LED bulbs can all be driven with the recommended forward current, with the dimming achieved by turning the LEDs on and off at high frequency - so fast the human eye cannot see the strobing effect. The longer the on periods are relative to the off periods, the brighter the LEDs will appear to the observer.

Simple google search.

http://www.reuk.co.uk/LED-Dimmer-Circuit.htm

I'm sure there is more to it than this, like building a circuit and controlling it manually. Might be more of a pain than anything else. Maybe get two different sets of LEDS, ones with a high Lumen output and the others with a low and something that will just switch the two.

**AudiA4Turbo22** · 12-11-2008 07:13 PM

make it like the LED tails when u push the brake they go bright u know same idea.

**rxrep** · 12-11-2008 08:12 PM

Originally Posted by AudiA4Turbo22

make it like the LED tails when u push the brake they go bright u know same idea.

Yup, except, how is it done?

**AudiA4Turbo22** · 12-11-2008 08:21 PM

try this website scroll down

http://www.mikesflightdeck.com/led_dimmer.htm

**B6 Dude** · 12-11-2008 08:29 PM

I can help you with this, but I first want to know how much current your LEDs (the whole string) takes. You can get it from the manufacturer's docs, or if you have a multimeter, disconnect one side of the LED string and connect the meter (in current mode) between the two open ends. Tell me what you get.