hardware control of 634 brightness


New member
As I'm using the 634 LCD in an embedded system, there is no keyboard/mouse, meaning no easy s/w adjustment of brightness. Is it possible for me to safely install a potentiometer through either the backlight's 5V or the GRD to control the brightness manually? If so, any recommendations on ohms, wattages?
Looking for additional LCD resources? Check out our LCD blog for the latest developments in LCD technology.

CF Tech

The 634's backlight is rated at 525mA to 650mA.

The "A" pin connects directly to "+5v(LED)" of J2.

The K pin is connected through R10||R12 through Q1 to ground.

The easiest way would be to vary the voltage on "+5v(LED)" down from +5v.

You could combine this with a "maximum brightness" by setting the backlight brightness and storing it in the EEPROM.

Probably a 5W 100 ohm pot would work fine, Digi-Key CT2154 for example.
USB LCD Displays - Graphic and Character LCDs with a Keypad