BFSK question -sensor input to binary FSK out

Discussion in 'General Electronics Chat' started by fsoender, Feb 1, 2016.

  1. fsoender

    Thread Starter New Member

    Dec 10, 2015
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    0
    Hi,

    Is there any IC out there that can help me out with a BFSK test.
    I got a sensor that I read, and converts the result to a binary string. I want this string send over BFSK protocol (0 and 1). Is there any good way or a IC that can do the job?
    I would want to change the frequency from 0Hz and up (speed)

    Can anyone help me?
     
  2. Picbuster

    Member

    Dec 2, 2013
    374
    50
    BFSK freq1 for mark freq2 for space. To give you an answer I need the frequency 1 and 2.
    sometimes 2 x opamp active filters or the analogue way two resonance filters will do.
    always detect both hence a=b is error and a!=b is correct.
     
  3. fsoender

    Thread Starter New Member

    Dec 10, 2015
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    I want the frequency to be 9Hz for "1", and 7Hz for "0"
     
  4. Picbuster

    Member

    Dec 2, 2013
    374
    50
    O dear that's close and low. The most simple way is to use a PIC. signal connected to interrupt. and measure pulse length or use counters.
    if you use the ints on high and low you double the number of pulses/counts creating a bigger numerical cap.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    9 Hz? Really? Are you a submarine?
     
  6. fsoender

    Thread Starter New Member

    Dec 10, 2015
    26
    0

    Sounds good, thanks!
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    How accurate do the two frequencies have to be?
    For super-low-rent, this can be done one opamp configured as a Schmitt trigger oscillator.
    Or with one 4093 or 40106 gate as a Schmitt trigger oscillator.
    For better accuracy and stability, the same thing can be done with a CD4060 (using a smaller value, higher quality timing capacitor).

    All of those methods are based on an R-C oscillator, with the data input switching in a second timing resistor. For real accuracy and stability, start with a watch crystal, divide it down to your low frequencies, and use the data stream to gate different decoded values back to the reset input. This would be a hardware version of what a microcontroller would do in software, but without all the typing.

    A PIC with an external crystal (the internal clock accuracy is not good) will be smaller, cheaper, and more accurate - IF you don't have to spend weeks or months learning PIC assembler or C++, buy a programer, blah blah...

    ak
     
    Last edited: Feb 2, 2016
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