LCD Backlight

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi,
I have got an 16X2 LCD HD44780 form Spark Fun working that shows a temperature reading. I am using the LCD 4 bit library and it works fine. My question is , how do I turn on backlighting? I believe this is available on pins 15 & 16 from the LCD.

Thanks

2

Look at the data sheet but normally you just apply power to the pins.

3

Just don't forget to check the documentation for the display to see if a current limiting resistor is needed.

I almost fried a display by not putting a currentlimiting resistor in line with the power to the backlight.

4

If it's an LED backlight, it almost certainly needs an external current limiting resistor. There's a chance it has one built in, but I wouldn't risk burning out the backlight by just applying power without confirming it.

LCD's also use EL-backlights, which are more difficult to power (they need high voltage, high frequency AC at very tiny current), but I doubt a nice modern purchase from Sparkfun would use that.

5

Hi - Thanks for the advice. Here are some of the specs from the datasheet.
Can I just connect a resistor and an on off type button between pin 15 and pin 1?

  1. 5X8 dots with cursor
  2. Built-in controller (KS0066U or Equivalent)
  3. +5V power supply(Also available for +3.0V)
  4. 1/16 duty
  5. BKL to be driven by pin1,pin2,or pin15,pin16,or A,K
  6. N.V.optional

Pin # Symbol Function

  1. VSS GND
  2. VDD +5V
  3. A +4.2V for LED
  4. K Power supply for BKL(0V)
6

Can I just connect a resistor and an on off type button between pin 15 and pin 1?

No,
It is pin 15 to Pin 2 through a resistor.
You will also need to connect pin 16 to pin 1

7
  1. A +4.2V for LED
  2. K Power supply for BKL(0V)

Just to clarify, A stands for Anode which you connect to positive, K stands for Cathode (yeah, it's confusing), which you connect to ground.