How to find the diode forward voltage, and diode forward Current

[RingOfStorms]

So I just got some IR-LED's for a new project. This is my first time doing large scale circuits with LED's and what not, so what I want to know is how can I find my LED's forward voltage, and forward current (mA). Also, when I got my IR-LED's it came with some resistors, but how do I know how many Ω resistance it has? So thanks, this is my first time on this site hope it helps.

 

[RingOfStorms]

BTW, I want to power my LED's with a modified ATX power supply from a computer I had laying around, which voltage should I feed into my large scale of IR-LED's? (I'm am going to be using about 100 of the LED's)

 

[MikeMl]

Do you have a Digital Multimeter?

 

[RingOfStorms]

not sure what you mean by that, im new at this like I said

and BTW the LED's are 940 and 5mm

 

[MikeMl]

Like **broken link removed**?

 

[Jaguarjoe]

The resistors you received are identified by the colored bands around them. There a bazillion websites that do color code deciphering. If that doesn't work, invest $3 in a Harbor Fright DVM. For a dollar more you can go high class with the backlit model. Use the ohms ranges to measure your resistors.

Just throwin' this out here-Using the 12v PS output, and assuming a Vf of 2 volts, 5 LED's in series would make the total voltage 10 volts. Once again, assuming an If of 20ma, you will need a resistor to limit the current from the 12v source to the 10v diodes. R = E/I = (12 - 10)/20ma = 2/.02 = 100 ohms. P = EI = 2 * 0.02 = 0.04 watts. A 100 ohm 1/4 watt resistor will work well. For 100 LED's, there will be 20 rows of 5 LED's. Each row will have its own 100 ohm resistor and consume 20ma. 20 rows at 20ma each will be 20 * .02 = 400ma total. You can do this with a 12v, 500ma(or more) wallwart.

If your Vf and If are different, rearrange the # of LED's in a row and the # of rows to get a total voltage of a couple of volts less than the supply and figure your current limiting resistance accordingly. LED's are pretty tollerant. 20ma is a real good number to run them at. The Vf can be found on any LED website. Every different color LED is made from a unique material with its own Vf.