Fixed 22/33 kHz function generator

Discussion in 'The Projects Forum' started by Sesnw, Oct 29, 2015.

  1. Sesnw

    Thread Starter New Member

    Oct 29, 2015
    4
    1
    Hi, I require some help with a project to make my day easier.

    I need to build two function generators, 22khz and 33khz.
    Both sine wave
    That will go through 5m of thin cable to earth.
    At a constant 1mA, so I can trace the signal from above for test purposes.
    Powered from any standard plug in power supply batteries not required.

    I can find DIY kits but nothing seems to get to the KHz required.
    I am no design engineer but have no issue building - could any body give me a point in the right direction please.
    I know I can buy a complex sig gen but I want something with a simple switch that if broken wont hurt to replace.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Google it. Are you sure you need a sine wave oscillator?

    With square waves, you could use a 555 timer, 2 resistors, and 2 caps for each oscillator.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Why do you need those particular frequencies?
     
  4. #12

    Expert

    Nov 30, 2010
    16,346
    6,835
    Testing what? (This reminds me of a broken invisible dog fence project.)
     
  5. Sesnw

    Thread Starter New Member

    Oct 29, 2015
    4
    1
    I am testing a 'cable locator' in radio mode which looks for 22khz then a simulated 33khz generated signal.
    22khz is produced by telephone cables underground and 33 is when you apply external signals.

    I want to build a simple test bed under concrete so users can quickly check there cable locators before the day's work so they know it functions - they have no tech skills and expecting them to use a signal generator is not reasonable

    Cable locator example
    http://www.amprobe.com/amprobe/usen...-and-pipe-locators-/amp-at-3500.htm?pid=73161

    Basically the signal is turned on the user runs there equipment over it and it should find the cable
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    How accurate do the frequencies need to be, i.e. what is the cable locator bandwidth?
     
  7. Sesnw

    Thread Starter New Member

    Oct 29, 2015
    4
    1
    Not very +\ - 10% possibly 20% it's a guide not a strict control to give the user confidence
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    So what about a square-wave output, such as dl324 mentioned, which would be simple to generate?
    It would have some harmonics of the fundamental included, but would that be a problem?
     
  9. Sesnw

    Thread Starter New Member

    Oct 29, 2015
    4
    1
    Yes I have been Google as suggested, and yes I think you and dl324 have a point, there are even some cheap off the shelf kits 'it was knowing what to google that helped'
    The difference in harmonics wouldn't give any issues considering my needs,

    Thank you both - big help :)
     
    ScottWang likes this.
  10. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    Try the rc phase shift oscillator circuit, it's easy to do, you can use two independent circuits.
     
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