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Author Topic: LCD Backlight current  (Read 3184 times)
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South East USA
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I can't find any info on this.
What's a typical resistor to use for the back light on a generic 16x2 LCD display with Blue backlight?
I'll connect it to the 5 volt pin.
thanks
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Central MN, USA
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Most spec sheets tell you what to do. In doubt, try a 150 Ohm. Then gradually dial up or down the number (with a pot) to find the brightness you need.

I would turn my lights off at night and dial the brightness just enough for comfortable viewing in the dark. In this case the back light is not visible in well-lit rooms, which doesn't need back light in the first place.

I'm sure someone will object the above and make their back light super bright  smiley-mr-green
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and if its too bright, you can always hook up a transistor and use pwm to vary the backlight. software is much easier to change than hardware smiley-wink
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Then gradually dial up or down the number (with a pot) to find the brightness you need
This is a bad idea if you are using the pot as a rheostat (with just two leads).  Unless you also use a fixed series resistor it's easy to burn out the potentiometer when you get down toward zero ohms.  You are OK if you use both the 150 ohm resistor and the pot.

Don
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I forgot to mention whoever does it needs to have a DMM to look at what initial resistance they have, well, an assumption I made.
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Then gradually dial up or down the number (with a pot) to find the brightness you need
This is a bad idea if you are using the pot as a rheostat (with just two leads).  Unless you also use a fixed series resistor it's easy to burn out the potentiometer when you get down toward zero ohms.  You are OK if you use both the 150 ohm resistor and the pot.

Don
Really? I would have figured the backlight LED(s) would burn out first to protect the potentiometer.  smiley-wink
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Katowice POLAND
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in my 2x16 blue lcd backlight takes 20-30mA in my yellow-green (that basic model) back light takes 300-400mA !
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I just ordered this from SparkFun.
http://www.sparkfun.com/products/709
white on black LCD...
the spec sheet says
typical LED voltage 4.2
typical LED current 120ma

so, on the 5volt pin, (5.0 - 4.2)volts/ .120 = 5 ohms?

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Yeah, just find a small resistor and stick it in there.
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