Changing the brightness on a Hitachi HD44780 LCD screen I am finishing up a project- an LED game alarm clock. Seeing as this is a clock, I need to have a way to conserve power, which right now my Uno R3+ is eating up like a politician. My question is, how do I turn the screen off, or turn the back-light off using software only on a Hitachi HD44780 16x2 LCD screen? Or how do I set a sleep mode on one component? The way I plan on turning it off is with an ultrasonic range finder, if I get close it turns on the screen. If anything I say doesn't make sense, ask me to clarify, I'm in a bit of a rush.
Place a transistor in series with a 33R resistor between the LCD pin 16 (backlight ground) and GND and switch the transistor on and off with a digital pin. That way you'll be able to turn the backlight on and off.

You can have a finer control over brightness if you put a PWM pulse on said pin. Just call analogWrite(D3, value) where value is the desired brightness.

The schematics is below. It's from Freetronics 16x2 LCD SHield.