Read HV Frequency into pic pin

Discussion in 'Embedded Systems and Microcontrollers' started by Art, Oct 13, 2015.

  1. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    Hi Guys :)
    I have made frequency counters for pics before with or without frequency dividers, etc.
    but always reading a lower voltage signal for radio and having to amplify it with a transistor or other amp.

    Now I want to read frequency from a voltage 12-30 Volts from the collector of a medium power transistor MJE3055T,
    and I’m not sure the internal clamping of the pic can be trusted that way.

    I can think of a few methods and wanted ideas of others.
    One way... current limiting resistor from the collector to a resistor divider, through to the pic pin,
    or current limiting resistor from the collector through a external diode clamp to the pic pin,
    or another transistor with it’s base connected via current limiting resistor to the collector,
    and the emitter connected to the pic pin.
    Do all of these sound viable? I do not want to influence much current or voltage of the circuit being measured.
    Cheers, Art.
     
  2. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
  3. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    Yes I have made a number of frequency counters with pics.
    The question is about interfacing one to a higher voltage signal than 5 Volts (or whatever the pic supply).

    So far i seem to have done well with this inductive coupling.
    There should be enough of a signal at least to drive a 2N3904 or similar transistor.

    [​IMG]
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    Attach the schematic may help the members to know more what are you trying to do.
     
  5. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    Hi Scott,
    I’m reading the resonant frequency of a slayer exciter in real time from this primary coil coupling
    and modulating a derivative of that frequency as audio over the same carrier so it can be audible with plasma.
    As you get close to the circuit (or Tesla coil) the resonant frequency varies all the time, so it’s nice to get an audible feel of it’s field.

    I only got the feedback part properly working tonight.
    Since it’s a relatively slow micro, only 2.5x instruction speed of the pic, it cannot count the resonant frequency,
    but I count the AC state of the coil’s primary 100 times per second
    and end up with a count that is at least influenced by what’s happening around the coil.

    There are a few tricks, one of which, the modulated audio frequency can’t be
    pulse modulated because the carrier must keep running to look at it’s frequency,
    so I’m AM modulating it between 100% and about 40% modulation.

     
  6. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    So you want to using the HV power to play plasma music as plasma speaker?

     
  7. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    785
    61
    Already doing that, but with smaller plasma for slayer exciter.

    But when the audio frequency is derived from the coil resonant frequency it works like a theremin,
    an instrument you can play with your hands.
    Any interference from your hands or surrounding objects changes the coil’s resonant frequency.

    This is the two parts of it.. reading resonant frequency and
    modulating an audio frequency, but not yet put together in this video:
     
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