Lilliput touch screen PWM backlight dimmer?

Discussion in 'The Projects Forum' started by Hardwyre, Sep 17, 2011.

  1. Hardwyre

    Thread Starter New Member

    Sep 23, 2010
    So I have a 669GL Lilliput touch screen that uses a LED back light. I'm going to use it as a home automation/home theater computer interface.

    What I am trying to figure out is how to get the back light to brighten/dim depending on the amount of light in the room. It has a manual dimming feature, but that dims through the LCD, not the backlight, and, well, it's manual.

    What I am hoping to build is a simple PWM circuit small enough to fit inside the monitor's case (there should be a little room; I'll know more once it's delivered).

    I'm wondering if there would be a way to use a typical 555 pwm circuit and add a photo resistor to brighten it when the room lights are on, and dim it when they're off. I got the idea from various smart phones.

    I'd imagine since the back light is simply "on" when the monitor is on, the PR/PWM could simply go in-line with the ~9.4 volt DC power.

    Think this is doable?
  2. RoboJam

    New Member

    May 11, 2011

    How are you supposed to access the programmable features of the 669GL Lilliput touch screen, if the facility for users to access the touchscreen data/control is permitted?

    I'm confused by the statement "It has a manual dimming feature, but that dims through the LCD, not the backlight, and, well, it's manual."

    Please explain a little further. I don't know what you mean by "It" has a manual dimming feature? Does that mean the LCD screen brightness? How is the LED backlight currently manipulated, if at all?

    Does the 669GL Lilliput touch screen run on an embedded system like WinCE?

    You could look into:

    a) CDS sensor with an opamp for brightness control interfaced to a microcontroller that has an onboard ADC.
    b) Digital Pot replacing an conventional pot with an SPI/I2C interface potentially?
    c) If a remote computer is "running" the home theater/home automation then you may want to craft interfaces that permit communication with the PC and run your software control application/utility on the PC in the background or in some sort of program, unless it has to be/you want it to be embedded.

    Good Luck