Arduino Tip : Built-in Pull-Up Resistors

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I’ve just found out a pretty awesome feature on the Arduino, or rather on all ATmega 328Ps.

Below is a simple circuit that uses an ordinary push button to light up an LED. Normally I’ll need a pull-up resistor as shown in the red box, but with the built-in pull up resistors, I can totally remove that part and save myself a resistor and some hassle when routing PCBs.

As an example, I’ll be using the sample sketch found in the Arduino IDE. It’s located under Examples -> 02. Digital -> Button.

The only difference was I added a line that enables the built-in pull up resistors.

digitalWrite(buttonPin, HIGH);

See the video below to see it in action :

The only downside is, it doesn’t have built-in pull down resistors.

This shouldn’t be too much of a problem because the normal practice in electronics will be to use pull-ups and detect LOW signals.

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  2. vick01-18-2013

    I think I can say like I HIGH the pin2 which is the buttonPin..Same concept.Hahaha.. Liike at the initial state, the PIN 2 is high by the CODE and not HIGH by the external pull up resistor to 5V.

    How if you define the pin as LOW ? then when press button supply a HIGH to that pin ?

    Just my thought.

    Thanks

  3. vick11-19-2012

    Keep RESET means the program won’t run?

  4. vick11-18-2012

    What is the purpose actually to pull up the RESET pins ? But I forgot I read somewhere they say no need..LOL

    • Wai Hung11-18-2012

      In electronics, the standard practice is to pull high and detect low.
      The reset pin detects a low to reset the mcu.

      If you don’t pull it high it will keep resetting.

  5. vick11-18-2012

    Means I no need to put any pull up resistor when use button for arduino ?

    • waihung11-18-2012

      Yup, for buttons you don’t need any pull-up resistor anymore.

  6. vick11-18-2012

    Does this means I do not need to put a pull up resistor at RESET pin (pin 1) ?

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