Resistor confusion

Quall · Post by **Quall** » Wed Jul 02, 2008 2:48 pm

I was reading the extreme-tech guide on modding the PSOne screen to use LED's.
http://www.extremetech.com/article2/0,2 ... 357,00.asp

The part that is getting to me is the resistor it says to use, which is a 10-ohm resistor.

Is that the guide everyone uses, and were there any problems? Please see my calcs below, am I doing something wrong? How much power exactly does the screen use?

Lets say I have 3 LEDs (in parallel), taking 25mA @ 3.5 volts each. So, 75mA or .075A total.

The source is 5 volts, so 5v minus the 3.5 from the LED's is 1.5v.
1.5v/.075A = 20-ohm's. Is it right to use a 10-ohm resistor over a something closer to 20? Am I doing something wrong?

Neildo_64 · Post by **Neildo_64** » Wed Jul 02, 2008 4:35 pm

This is a handy website for figuring such calculations. http://www.ledcalc.com

Quall · Post by **Quall** » Wed Jul 02, 2008 5:13 pm

Thanks, the site seemed to work well and verified my calculations.
It recommended a 22-ohm resistor.

I guess that is my answer, but if anyone used a 10-ohm resistor and followed that tutorial, I am curious to know if your LED's are still alive.

I will buy a few 10's just in case.

Sharp Sapphire · Post by **Sharp Sapphire** » Wed Jul 02, 2008 6:19 pm

That got me also.

I bought both 22 and 10 ohm resistors just 5 minutes ago. I'll try out both.

Sharp Sapphire · Post by **Sharp Sapphire** » Thu Jul 03, 2008 8:38 pm

Sorry to bump but I have an update.

My LED's emitted BLUE when I hooked up a 10 ohm resistor... definitely not good... 22 ohms is perfect though!!

Quall · Post by **Quall** » Fri Jul 04, 2008 7:48 am

Thanks for the update. I ordered some LED's and expect them sometime next week. I guess I will start with the 22-ohm first.