LED Taillights, Diy

[Matt21lutz]

Originally Posted by ray_mcavoy

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.

The LED's that im using are from superbrightleds.com, http://www.superbrightleds.com/morei...-mcd/356/1303/ they are EXTREMELY bright when wired correctly, ive got one small board sitting on my wall hooked up and working, i use them as a night light when i'm working late at night lol well with a resistor and witch they're a night light and then flip the switch for full brightness.

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.

as far as wiring in parellel... yeah that'd be too much for me, i could do it but I'll just end up buying the right resistors online for 10 cents each or something like that lol

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.

I think I might try the adjustable one, I could always set it to 12v and use a resistor if that is what i go with.