CFAG12864B-TMI-V Backlight Problem

[KE4NYV]

I just received one of these graphic LCDs and started to write some PIC code for it. I noticed that when I first hooked it up the backlight was fairly bright, but not alarmingly bright, as to indicate too much voltage. After a day of experimenting, the backlight appears only about half as bright now. I did'nt chnage anything in wiring and it has been tied to 5VDC all along.

Has anyone else seen this? Did I just get a faulty LCD?

Thanks,
Jason.

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[CF Tech]

Connecting it directly to 5v will kill it.

There is some text here on connecting backlights, but you definitely need a dropping resistor. For 5v and 60ma:

RLED = (5v - 3.5v) / 0.060A = 25 ohms

 

[KE4NYV]

Damn, well theres a first for me and CF LCDs. Never have had one die like that until now with 5VDC.

Just saw your PM, I'll go take care of that now.

Thanks.

 

[CF Tech]

The yellow LEDs should also have a dropping resistor, but they are more tolerant to the abuse of having +5v hooked directly across them.

So if it was a yellow backlight that you had hooked up that way before, that might explain why you were able to get away with using no dropping resistor.

 

[KE4NYV]

OK, well I keep a stock of 2W 39 Ohm resistor for things like this, so I'll give that a try with the replacement I have comming.

Thanks,