Hi Guys,
I have two LCDs, one of which seems bright the other which is very dull.
Both LCD LEDs are wired to a 5V line with a 220ohm resistor in the way dropping it down to 3V, however upon reading the spec sheets it appears the LED is meant to get 5V?
Can someone confirm as I know providing too much voltage to a LED will burn them out...
http://www.datasheet-pdf.com/datasheetdownload.php?id=710096
A 220 Ohms resistor is commonly used to limit the current drawn by an LED, it's not dropping votage to 3V.
There is no potentiometer to control the brightness of the LCD?
The specifications for the backlight LED are poorly written.
From this specification on page 5, it shows pin 15 at 5.0V.
At the bottom of page 5, it says operating voltage 4.1(±0.15V), 100mA max. forward current.
To be safe, I would use a series current limiting resistor connected to 5V and the other end to pin 15.
Then ensure that the operating voltage 4.1(±0.15V) and 100mA current is not exceeded.
Example: Using R = 100Ω, I = (5-4.1)/100 = 9 mA (untested) Voltage at pin 15? (untested).
Example: Using R = 27Ω, I = (5-4.1)/27 = 33 mA (untested). Voltage at pin 15? (untested).
Let's presume for a start that when you refer to "bright" or "dull", you are referring to the intensity of the LED backlight.
The contrast potentiometer does not control the LED in any way, but must always be adjusted for optimum readability and apparent brightness.
The datasheets tend to be generic, covering various models of the display with different possible LED arrangements.
Check resistors R8 and R9 on your module. Generally, one of them will be "101" or 100 ohms and the other - if present - zero. If the 100 ohm resistor is present, then it is safe to connect pin 15 directly to 5V and pin 16 to ground.