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Calculating resonant frequency in series RC oscillator

  1. Jan 6, 2006 #1
    What is the formula to calculate the oscillating (resonant?) frequency of a series RC circuit with a constant DC voltage?

    For example the RC circuit shown at this site:

    http://www.mikroelektronika.co.yu/english/product/books/PICbook/2_02chapter.htm" [Broken]

    How does this circuit resonate with a DC voltage? Aren't capacitors supposed to act like an open circuit to DC voltage?

    I have searched all over using google but cannot find details on RC oscillators.
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jan 6, 2006 #2


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    There is more going on inside the microcontroller than you are able to see. The RC circuit sets up a time constant. When the voltage is first applied to the circuit there is a specific amount of time it takes before the voltage at the node of the capacitor and resistor reaches a specific level.
    Think of it this way: The microcontroller senses this voltage and modifies the circuit to discharge the capacitor at a specific rate. Then it senses a lower limit and allows the capacitor to charge again.
  4. Feb 1, 2006 #3
    I'm no expert but it sounds like the 555 timer chip. This chip uses capacitors and resistors as a reference time constant, then from this creates a pulse signal. By the way the output of the 555 timer is not strictly A/C sinsoidal but sawtooth.So almost like using a rapid on/off switch with C & R setting the speed.
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