I’ve got black wire painted red, and red wire painted black, and sometimes the wire color alternates from board to board.
Being color blind might might be an advantage sometimes!!
Regards, Greg
An old friend, Pastor Doug, is totally color blind. Has absolutely no idea what color he’s looking at. Fresh out of HS, he tried to go into electronics. Resistor color codes were a complete mystery to him. He’s now quite content as a preacher, though people around town are amazed, “Doug’s a preacher?!?!?!” Before Trinity started school, she palled around with Dad all the time. He’d ask her to match colors for him. We never told him he painted the old ping-pong table pink.
(http://www.outsidetrains.com/facillity/100_1101.jpg)
Mariah (blue) and Trinity (pink) visiting my shop. Kids loved playing with old track and a plastic wheelset.
To calculate the resistor needed for 20 ma leds, you need 50 ohms for every volt dropped.
So a 3 volt led on 14 volt battery is 11 volts times 50 ohms, giving 550 ohms. Standard 560 ohm resistor needed.
for 5 volts, only 100 ohms needed for 3 volt led.
For 10 ma leds, you need 100 ohms for every volt dropped.
Another factor not mentioned is the power rating of the resistor. 20 ma at 10 volts is .2 watts, minimum is 1/4 watt, but I like going at least double on this rating, so 1/2 watt is what I would use.
I use this site for calculating resistance for a single led.
http://led.linear1.org/1led.wiz
This site for multiple led wiring -
Dan, I’m just curious… why did you revive a thread more than 2 years old to tell someone how to calculate a resistor?
How did you come across this thread? It surely was buried layers deep.
Again, just curious, you have the right to dredge up any old thread.
Greg
Greg, I was just browsing around LSC and did not watch the dates.
I thought maybe it was to bring up my offer of giving away my house and cars ha ha!
Greg
GE’s “warm white” LED Christmas lights are ridiculously close to the color of incandescent bulbs. (And seeing as how July’s almost over now, you should start seeing Christmas stuff in the stores in a week or two. 
) Seriously, though, a strand of 50 will set you back at most $10 early in the season, or $4 at the end of the season. You can also get packages of replacement LEDs for around $2 for 10 LEDs. They’re small - 3mm LEDs, but put out a lot of light especially if you sand the outside of the LED to diffuse it. The size is nice because they fit into class and marker lamps with no problem.
Later,
K
You shouldn’t knock LED drivers until you’ve tried them. No calculations and dirt cheap. From Mouser the shipping exceeds the cost of a dozen of them.
Greg Elmassian said:
Dan, I'm just curious... why did you revive a thread more than 2 years old to tell someone how to calculate a resistor?How did you come across this thread? It surely was buried layers deep.
Again, just curious, you have the right to dredge up any old thread.
Greg
Once again this thread from 2009 rises to the top!
Who was knocking LED Drivers? Nothing wrong with them, but pretty much unnecessary in my applications.
I use LED driver for everything, I luv them. Quick and easy.
The LED drivers have some advantages. If you have standard voltage, standard LED, and you can use a standard, easy to find value of resistor there’s probably little advantage.
(as I would suspect is your application Jon)
On the other hand, if you sometimes use 2 or 3 in series, or have variable input voltage, they are superior to resistors in ease of use and safety to the current supplied.
Greg