[stunner]

So... I got a PM from another forum member asking me if I would build him a Tic-Tac LED brake light like the one I built for myself HERE.

I really didn't feel like working today so...

Here are some progress pics:

[stunner]

Some more progress pics:

[stunner]

A few more:

[stunner]

Finished!!

[berettajeep]

Very nice! I think I will "borrow" this design for some rock lights.

[SinCityCJ]

Very cool. Gave me a few ideas for some places I need some lighting. What ohms were the resistors you used?

[stunner]

Originally Posted by SinCityCJ

Very cool. Gave me a few ideas for some places I need some lighting. What ohms were the resistors you used?

The LEDs were 2.4V @ 20ma so, to run on a 12V-14V system I needed 240-270 Ohms. I used two 120 Ohms resistors in series to achieve 240 Ohms!

[mark02tj]

Originally Posted by stunner

The LEDs were 2.4V @ 20ma so, to run on a 12V-14V system I needed 240-270 Ohms. I used two 120 Ohms resistors in series to achieve 240 Ohms!

OK, DUMB question from a non-electronics person. How did you know that you needed 240-270 Ohms? I'm sure there's some sort of formula to knock 12V down to 2.4V but I'd have no idea even where to look for something like that.

THANKS!!

[stunner]

Originally Posted by mark02tj

OK, DUMB question from a non-electronics person. How did you know that you needed 240-270 Ohms? I'm sure there's some sort of formula to knock 12V down to 2.4V but I'd have no idea even where to look for something like that.

THANKS!!

Dude, the only DUMB questions are the ones never asked!!

Actually, if you wire the LEDs in series it looks something more like this:

2.4V + 2.4V + 2.4V = 7.2V (Because I used 3 LEDs)

So, you need to bring the 12V down to 7.2V.

The formula is: R = (VS - VL) / I

R = Resistor
VS = Supply Voltage
VL = LED Voltage
I = LED mA (or current)

So for what I did:

[12V - (2.4V + 2.4V + 2.4V)] / 20mA = .24 or 240 Ohms

It's 240 and not .24 because it's 20mA (which is miliAmps so, you move the decimal over by 3).

Hope this helps!!

[mark02tj]

Originally Posted by stunner

Hope this helps!!

Helps a lot!! THANKS!!

So if you would have used 5 of the LEDs, you wouldn't have needed any resistors (5 x 2.4v = 12v) ?

It's been since high school (almost 30 years) since I've had an electronics course so I could use a refresher.

Next dumb question - can you "dim" LED's like you can dim an incandescent bulb? I'm guessing "yes" since there are the LED taillights with brakelights. Or, do those have two sets of LEDs in them - one for the taillights and one set for the brakelights?

If you wired a pot into the circuit, would that act as a "dimmer" on the LEDs?

Oh, Mr. Lowmiller (my HS electronics teacher) is spinning in his grave!!

THANKS again for your help!!

[stunner]

Originally Posted by mark02tj

Helps a lot!! THANKS!!

So if you would have used 5 of the LEDs, you wouldn't have needed any resistors (5 x 2.4v = 12v) ?

It's been since high school (almost 30 years) since I've had an electronics course so I could use a refresher.

Next dumb question - can you "dim" LED's like you can dim an incandescent bulb? I'm guessing "yes" since there are the LED taillights with brakelights. Or, do those have two sets of LEDs in them - one for the taillights and one set for the brakelights?

If you wired a pot into the circuit, would that act as a "dimmer" on the LEDs?

Oh, Mr. Lowmiller (my HS electronics teacher) is spinning in his grave!!

THANKS again for your help!!

Howdy!!

You can definitely dim LEDs... you'll need a low voltage dimmer (essentially a pot). You can get one at radio shack or take one off a car from the junkyard (those work too!).

I've never tried the potentiometer approach but, I'm sure it would work. I would get one that would let you turn it to full voltage (12v) as opposed to the more precise ones like a 1k... I guess it depends on your application.

Have fun!

[JaikYJ]

Those look really good, thats a great home made mod!!
Cheers for sharing.

[green_jeep]

Cant wait to mount it up on my jeep!!!!!!!!

[green_jeep]

got it mounted up on my jeep but mounted it a lil different then u did Stunner.
i took my plastic center cap off my spare tire cut a hole in it for the tic tac box to fit into then used silicone to make it stay there nice and tight.ran the wires with a plug (so if i have a flat i can take it off put it in the glove box).
painted the centercap flat black so you can hardly see it when its not lit. no pics yet but i'll snap a few tomorrow when i have someone to hit the brakes, and daylight so you can see it in the day.
Thanks again real nice lil light!!!!!!!

[green_jeep]

ok couldnt wait 2X4 block of would on the pedal and a mini mag light works LOL