LED Active Low



  • There's the push button board drawing for one pin.

    Same maker as LED board.

    Drawing will have to do until they send me the schematic.

    I need to change gears from thinking about LED board.

    Okay.Reading the pin this time.

    What does it read when button is not pushed?

  • Reads "1" or high when button is not pushed, "0" or low when pushed.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • PB0       PIN    0
    Pushed    CON   0
    IF PB0 = Pushed THEN
    Re-inventing the wheel is not a waste of time if, when you are done, you understand why it is round.
  • microcontrolleruser,

    That's an active-low pushbutton because the pushbutton is connected to Ground.
    Also notice the 10K pull-up which "pulls up" the I/O pin to Vcc.

    As Tom mentions, you will see 1 on the I/O pin because of the pull-up resistor, but as soon as you press the button it will change to 0.

    Most of the pushbutton circuits in What's a Microcontroller are active-high which is easier to understand.
    You see a 0 and then when the button is pressed it changes to 1.

    Active-low buttons are handy when you want to know if something is there.
    Say for example you want to know if a door is open so you have the switch be on or active when it's closed.
    Then it's easy to see if the door is open because the value will change to 1.
  • microcontrollerusermicrocontrolleruser Posts: 1,194
    edited 2018-04-09 - 00:13:27
    'Active-low buttons are handy when you want to know if something is there.'

    Like your circuit that you are building the first time.

    It's fail safe when you use active low.

    If you are reading a zero on active high circuit it could be an open circuit but that can be easily tested.

    Now I think it is more a case of when these board were designed the

    micro's were better at putting out a 0 logic than a 1 logic.
  • microcontrollerusermicrocontrolleruser Posts: 1,194
    edited 2018-04-09 - 00:17:37
    Look at the board.

    That is 90's era.

    Oops! That's LED board. Okay. Pusthbutton board looks the same.

    300 x 224 - 25K
Sign In or Register to comment.