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
    26
    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

    Well-Known Member

    Dec 2, 2013
    827
    101
    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

    Well-Known Member

    Dec 2, 2013
    827
    101
    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

    AAC Fanatic!

    Aug 1, 2013
    7,165
    2,018
    9 Hz? Really? Are you a submarine?
     
  6. fsoender

    Thread Starter New Member

    Dec 10, 2015
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    0

    Sounds good, thanks!
     
  7. AnalogKid

    AAC Fanatic!

    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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