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Pull-up resistor value

Home Forums MPLAB XC8 Tutorial Discussions Pull-up resistor value

This topic contains 2 replies, has 2 voices, and was last updated by  Italo Balbo 3 weeks, 5 days ago.

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  • #5027

    Italo Balbo
    Participant

    Hi

    I’m wondering how you choose the value 10k ohm for the pull-up resistor in the input pin of the pic. Is 220 ohm, or any another value, ok too? Thanks

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  • #5030

    Bitahwa Bindu
    Keymaster

    Hi,

    There is no exact value that should be used as a pull-up resistor, but you must always consider that the larger the resistance of this pull-up resistor, the slower the pin is to respond to voltage changes, this is because the system that feeds the input pin is essentially a capacitor coupled with the pull-up resistor, thus this forms an RC filter, and RC filters take some time to charge and discharge. So if you have a very fast changing signal (like USB for example), a high value pull-up resistor can limit the speed at which the pin can reliably change state.
    And on the other hand if you select a lower resistance value, when the switch is closed, more current will be routed to ground which is not a good idea especially if the circuit is battery powered, your circuit will consume more current unnecessarily which can drain your battery quickly if battery powered. A value from 4.7K to 10K is generally used, but based on your unique requirements, you can change this value accordingly.

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