Flash controller for 12V brake/tail system

Hi all,

I am trying to build a controller to flash an automotive LED brake/
tail light. The light has a 3-wire interface: white is ground, while
black/red select output brightness level. All LEDs are lit,
regardless of brightness. I'm not sure how this is accomplished
internally (the light is a 3-wire black box to me, I can't crack it
open).

During operation, I want the light to alternate between low and high
output modes (frequency/duty TBD...most likely something in the 2 Hz -
5Hz range). The simplest way as I see it is to connect the 'low' wire
to +12V and then have the 'high' wire get switched on/off by a simple
timer (a 555 in astable mode seems right for the job). I haven't
measured the current through the device yet, but I believe that it
will be more than the ~200 ma the 555 output can handle.

I want to avoid a relay if possible...so a power transistor (as a
switch) seems to be the way to go. The designs I have seen show the
(NPN) transisitor emitter connected to ground and the load connected
to the collector...clearly no good for this application since the
switching must be done on the 'positive' side of the LED.

This is a simple problem, so I'm sure it has already been solved.
Does anyone have any ideas (or links to good online resources)?

Cheers,
Dave

.

Relevant Pages

  • Re: Status Indicator System
    ... Each switch would correspond with an indicator in the family ... for that person to reset the light at the shelf when they picked up ... Purchase a 12 folt DC wall wart and n LEDs plus n 1K ... Wire up your LEDs and resistors like this: ...
    (sci.electronics.basics)
  • Re: Installing an LED
    ... would like to do is wire an LED to a Roland FS-1 foot switch pedal. ... pedal switches between two channels on my guitar amp and I would like to put ... those 2-color LEDs from Radio Shack you can hook ...
    (sci.electronics.misc)
  • Re: Front panel headers
    ... red & white hdd led 2 pin Can I assume that red is positive? ... purple & white reset switch 2 pin Can I assume that white is gnd? ... so the wire and crimp pin can be pulled out. ... The LEDs are polarized, and can be installed the wrong way without ...
    (alt.comp.hardware.pc-homebuilt)
  • Projects on www.myblueroom.com, which one would you like to see first?
    ... Like a DIY Aprilaire or RCS RS232 thermostat. ... iButton thermostat ... switch or GP inputs ... zone status LEDs ...
    (comp.home.automation)
  • Projects on www.myblueroom.com, which one would you like to see first?
    ... Like a DIY Aprilaire or RCS RS232 thermostat. ... iButton thermostat ... switch or GP inputs ... zone status LEDs ...
    (comp.home.automation)