Display Tech 204A Backlight problem

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi all,

I have just received two 4 x 20 character LCD's from RS (532-6818) and the backlights on both are very dim when connected to my Arduino Mega 2560.

Code:

#include <LiquidCrystal.h>

LiquidCrystal lcd(33, 31, 29, 27, 25, 23);

void setup() {
lcd.begin(16, 2);
lcd.print("hello, world!");
}

void loop() {
lcd.setCursor(0, 1);
lcd.print(millis()/1000);
}

Pin 1 - Gnd
Pin 2 - 5v
Pin 3 - Wiper on 10K pot for contrast
Pin 4 - Arduino pin 33
Pin 5 - Gnd
Pin 6 - Arduino Pin 31
Pin 7 - N/C
Pin 8 - N/C
Pin 9 - N/C
Pin 10 - N/C
Pin 11 - Arduino Pin 29
Pin 12 - Arduino Pin 27
Pin 13 - Arduino Pin 25
Pin 14 - Arduino Pin 23
Pin 15 - 5v
Pin 16 - Gnd

Any thoughts on why it might be so dim?

2

You cannot connect the backlight (pin 15 and 16) directly to 5V power source without a resistor.

I looked at the datasheet that I found from RS Online site, the maximum voltage and supply current for blue/white/green LED backlight is 3.5V and 25mA. A resistor with a value between 68 ohms and 82 ohms can be used.

For other voltages for the backlight see the datasheet:

http://docs-europe.electrocomponents.com/webdocs/06dd/0900766b806dda1c.pdf