PIC ADC - Current Limiting Resistor Req'd?

Discussion in 'Embedded Systems and Microcontrollers' started by elementalrage, Dec 15, 2009.

  1. elementalrage

    Thread Starter Active Member

    Jul 30, 2009
    59
    3
    I'm just using a PIC to read a voltage divider will give readings between 0 and 5 volts. Do I need a current limiting resistor before it hits the ADC pin on my PIC?
     
  2. Dalaran

    Active Member

    Dec 3, 2009
    168
    0
    What values are you using in your current divider? I never have used a current limiting resistor on the ADC inputs and have had no problems.
     
  3. elementalrage

    Thread Starter Active Member

    Jul 30, 2009
    59
    3
    I have a 1k on the 5 volt side and a 20k potentiometer on the other. Ranging from ~500ohms to 20k.

    5v >> 1k ohm : ADC pin on PIC : 0~20k ohm >> 0 (GND)
     
    Last edited: Dec 15, 2009
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    To need a voltage divider, you must have a voltage to measure that exceeds the range of the ADC. As long as the divider does not load the input signal and distort it, it should work.

    What is the amplitude of your input?
     
  5. elementalrage

    Thread Starter Active Member

    Jul 30, 2009
    59
    3
    I have voltages roughly between 1.7 and 5 volts.
     
  6. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    There is no need to use a resistor if you are within the voltage specifications, in fact it could cause accuracy problems if you used a high value.
    From 12F629 datasheet:
     
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