Technical > Electronics > I need some brains to pick :)

What (number) bulb are you trying to replace? I'm pretty sure I have already seen dual brightness LED's designed to replace Automotive tail lamps.

Not sure how they are doing it exactly, but I think they are using different brightness LEDS for the different filaments. So you put the low output LED's on the running lamps, and the high output LEDS on the brakes.

Here is one place..
»www.superbrightleds.com/cgi-bin/···2x19.htm

You can see they list 2 different current Draws for the 1157 dual filament replacement.

It can be done with resistors, but an LED driver is much better.

The dimmable LED driver that you linked to 3021-D-E-#### is not perfect but suitable. The reason that I'm saying that it isn't perfect is that it will still require a bit of additional circuit to make it fully functional for your purpose.

The '-D-E' in the model number indicate DC voltage input and External dimming controls.
The -#### is the maximum output current (full intensity) which you need to choose based on the requirements of your LEDs.
You will need a 5KOhm potentiometer to set the dimmed output current and a relay to switch between maximum and dimmed intensity. You will also need two diodes to provide power to the LED driver from both high and low intensity power.
For the potentiometer use a 10-turn precision potentiometer (you don't need the precision, but those are less likely to change their value while driving). The relay can be any automotive relay with NO and NC contacts.

The exact circuit depends on how the current turn signal/parking light bulb is powered. Is the bulb common ground with two +12V contacts for high/low intensity or is it common +12V with two ground contacts ? Is it possible that both high and low intensity are active at the same time ? If so, what should the intensity of the LED be if both are active (probably bright) ?

The contact needs to switch at most 5mA and the relay you linked to is rated for 500mA. I just hope the coil current is a typo, the specification says 4.2A (probably is 4.2mA).

The difference between the 3021 and 3023 is pins vs. wires. Choose whichever works better for you.

The 'I' models have an internal potentiometer, but don't work for you since they can only be set to one intensity. You need the 'E' models with external potentiometer (not included with the LED driver) so that the relay can switch between full and partial intensity. This way you need only one driver (for each LED star) for both intensities.

are you sure the flash circuit will operate correctly with LED's being used instead ?
i changed mine with a home-made LED set and the flash circuit operated like it was on crack

haha but the LED flasher would be better because it's just replace and go!

I apologize for the crude drawing, but I'm clearly not an artist.

The two diodes should be rated at the very least for 1A, better more. I would use 1N5400 - 1N5408 (3A general purpose rectifier diodes).

Not shown in the diagram are the following optional components:
- Resistors from +12V to Ground if needed (flash frequency, current based failed bulb detectors)
- Capacitor from +Vin to -Vin (suggested in 3021/3023 datasheet)

The circuit is really simple. With no power on either +12V Park or +12V Turn the LEDs stay dark (big surprise?). With power on +12V Park only, the relay does not engage and the NC contact causes the LED current to be limited by the potentiometer setting (dimmed LED brightness). With power on +12V Turn (regardless whether or not +12V Park is present too) the relay engages and opens the NC contact. The full 5kOhm resistance of the potentiometer connects between the Reference output and the Control input causing maximum brightness of the LED.

In both cases (bright and dimmed) the LED intensity is controlled through the current regulation in the LED driver module.This means that the intensity of the LEDs is consistent regardless of any variations in the car battery voltage.

wait I think I can use these here, no?

»www.mouser.com/Search/ProductDet···8-1N5550

Wait are you saying the two relay way would make the LED flash like it does now? I'm still not fully understanding why I would need an extra relay I thought it would do the same with just one.