LED Taillights, Diy

[ray_mcavoy]

Originally Posted by Matt21lutz

awesome, I did see that it said for vehicular use on that just wanted to make sure. and as far as the diodes actually taking away some voltage.. i would have never thought about that unfortunately when i ordered all my resistors i got 56 ohm as the smallest ones, i could always buy more but then im paying triple just for shipping a few dollars worth of resistors, but i might. The only thing would that would be different is the 56 ohm would make the led's dimmer , just not sure how much actually... we'll find out! I'll probably make a few tester first then make the final product.

You're right ... they'll definitely be dimmer than normal with 56Ω resistors on a 12V supply after you add in the diode drop. And without some additional data on the LEDs you're using, it's hard to say just how dim they'll be.

You can put some of the 56Ω resistors you already have in parallel to obtain lower resistances. To calculate the total resistance, add the reciprocals and take the reciprocal of the sum. Rtotal = 1 / ((1/R1) + (1/R2) + ... + (1/Rn)). So 3 of those 56Ω resistors in parallel = 18.7Ω ... and that's pretty close to the 15Ω I calculated earlier. Using 3 parallel resistors for each LED string obviously isn't something you'd want to do for your final design (it'd be a waste of resistors & board space). But I thought I'd mention it because it's something you could do for preliminary testing on a string or two of LEDs without having to buy more resistors.

Originally Posted by Matt21lutz

But i would like to get your opinion on something else that i thought about, what do you feel is the best way to dim the led's? with a 1/2 watt resistor or to use a voltage regulator with a lower output voltage? for instance a 10v output.

Either one will work (and there are several other ways as well). The resistor is simple and will get the job done. Unless you've already done so, you might need to try a few different resistance values to get the brightness of your tail lights to the desired level.

If you use a lower output voltage regulator, you might want to consider an adjustable regulator instead of a fixed 10V output. That'd allow you to easily change the output voltage in case 10V ends up making the LEDs too bright or too dim. The LM2941T is an adjustable version of the LM2940T-12 fixed 12V regulator you're considering. The output voltage is adjustable using the ratio of a couple of resistors. And for testing purposes you could use a potentiometer.

Originally Posted by Matt21lutz

but thank you for all the help so far as well! i greatly appreciate it!

You're welcome!

Originally Posted by kikkegek

I have already build a couple of these tail lights for myself.

see my sig for the end result.

here is a link to the build topic of it on HID PLANET
http://www.hidplanet.com/forums/show...or-my-Suburban

Nice job! I didn't get a chance to read through all the details, but it looks like you used the LM2940T-12 regulators that Matt is considering, correct?