# Backlight on a CFAH200AA-GGB-JP

#### Beers

##### New member
Hello

I wired my first LCD up (the blue background with white text ones) and I must have put the 12 volt wire on the + terminal instead of 5 volt wire. At that point i had already soldered a lot thinking it was a short, but then came back and realized that i probably shorted it out.

I have my new LCD screen currently all wired up and working. It interfaces with the host computer and everything.

Then i get to backlighting.
I came to the site and looked around. All the posts are about the formula to find the right resistor. I calculated that i needed a 3.57 Ohm resistor.

My question is, Where can i find a resistor that low? or could I just hook the backlight directly up to the power? (~5.2 volts)

I used:
(5.2-4.6) / .280 = 3.571... My power supply outputs at about 5.2v now. It may change once its in with other circuits and devices.

Any suggestions? I checked radio shack and they dont have that low of a resistor.

Thx
PS- sorry if i rambled, its 3am
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#### CF Tech

See the full calculations here.

Based on the data sheet for the CFAH2002A-GGB-JP, I get (5.2-4.2)/0.21 = 4.76 ohms.

So in that case, get two of Radio Shack's 10 ohm resistors an put them in parallel. That will give 5 ohms.

#### Beers

##### New member
OK ill try that, hopefully that works out. Thanks!

#### Beers

##### New member
I got another question now.

I got two of the 10 Ohm resistors and put them in parallel and got around 5 Ohms, thats good.

I hooked it all up, backlight works. Good level of brightness is given off.

After having it on a while, i noticed the resistors got a lil warm. Is this normal??

Thanks again!

#### CF Tech

Yes, they will be warm. Here is the equation for the power (heat) dissapated in a resistor:

Pres = Vres * Ires

Pres = (5.2-4.2) * 0.210 = 210 mW

or about 1/5 of a watt of electrical energy will be converted to heat in the resistor.

#### Beers

##### New member
Yeah, i calculated that too, but I wanted to be sure that the resistors being warm wasnt a big issue.

Everything is working great, its in its little box, and now im writing code to interface with it.

Next time i may go with the serial LCD because they look to be better, but im going to wait till you have 4x20 with keypads + the color variation like the CFAH's.

Thanks again,