leds

[reddragon]

 I have some LED's that i wont to use and the specs

     smalls---2 volts at 10 MA

     large----3 volts at  20 MA

I don't know the size of reastants to use with them they will be powred by 12 volts is the a way to tell how much reastants for LED's????

[JonnyMac]

Ohm's Law is our friend: E = IR (volts = current x resistance)

In a series circuit the voltages add up, so if you have a 12-volt supply and are using a 2-volt LED then the current limiter (resistor) will have 10 volts flowing through it.  Another important point about series circuits is that the current flow is the same through all components -- so if we want 10mA through the LED we calculate the resistor for 10mA.

We can rearrange Ohm's Law to help out: R = E/I (resistance = volts / current).

So, if we take 10 volts and we divide it by 0.01 (10mA) we get 1000 (1K).  A 1K resistor is marked Brown-Black-Red.

For the 3-volt LEDs at 20mA the current limiter would be 450 (9 / 0.02) -- the closest standard value is 470 (Yellow-Violet-Brown).

[reddragon]

 thank you i forgot how to do the ohm's law thank you Jon.

[QPQ]

It's nice to know the real way to figure that, but if you question yourself or would like to see it wired on screen, here's a very easy to use calculator  (especially for multiple arrays)http://led.linear1.org/led.wiz

As always though, Jon is awsome - nobody supports like him!

Have fun,
Ron

[reddragon]

 :) thanks Ron, hope everone had a good haunt my was good planing for next year....