Project using 35 ma with LCD turned off?

Discussion in 'Embedded Systems and Microcontrollers' started by spinnaker, Oct 30, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    I have a PIC project using an LCD.

    The back light and LCD are being powered by one of the pins of the PIC.

    When the light and LCD are on the whole project draws around 12 ma. When the light and LCD go off the current was jumping to 35 ma!

    I noticed that in my code I was still writing to the LCD even though it was off. I changed my code to not write to the LCD. Now with the light off, the project draws about 6 ma.

    Why was the project drawing so much when the PIC was writing to the LCD?

    Also I noticed that if I turn RS on (RS only), the LCD back light, lights dimly. Why would this be happening?
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    What is a "BuckPuck"?
  3. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    The buckpuck is not yet in circuit. It is a off the shelf buck regulator for driving an LED array.
  4. AlexR

    Well-Known Member

    Jan 16, 2008
    In all probability your LCD backlight is drawing more current that a PIC pin can supply.

    The maximum current that any I/O pin can supply is 25mA and the maximum total current a port can supply is 200mA.
    You don't say how much current your LCD backlight draws but typically they can take around 70mA.

    It could be that with the backlight on the PIC is shutting down and limiting the current to 12mA, with the backlight disconnected everything is working normally and the PIC and associated circuitry combined is drawing 35mA.
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Backlite shud be driven via transistor off the main supply