33 KHz transmitter

Discussion in 'The Projects Forum' started by Blangdk, May 24, 2015.

  1. Blangdk

    Thread Starter New Member

    Aug 21, 2014
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    I have a CCTV inspection camera for pipe inspections and the inline transmitter is is dead. I am trying to make my own replacement for it but am struggling a bit with the coil needed.

    How do I work how many windings I need and can I do it without an iron ferret?

    I need to be able to locate it through the ground using a 33KHz locator.

    Hope someone out the can help me.

    Cheers.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I would hope so ;). Seriously though, can you post a schematic of the transmitter?
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    http://en.wikipedia.org/wiki/Ferret

    Using the wrong word creates a really bad impression. I'm not sure we can help you without more information than you have currently provided.
     
  4. Blangdk

    Thread Starter New Member

    Aug 21, 2014
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    What a shame. I was hoping to have a real life ferret in there. Apologies for my minor brain seizure. Obviously talking about a ferrite.

    I have attached a schematic of what I was thinking. I was looking at using the Pic to divide the frequency of the crystal to the 33KHz and then have the FET square it out.
    I haven't done the programming yet, nor determined any values in the circuit yet.

    If you guys have any suggestions to the circuit as well, I am all ears.

    Cheers.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    So the 33 KHz. signal is used to locate the inspection camera. How do you access the video data?
     
  6. upand_at_them

    Active Member

    May 15, 2010
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    The camera is attached to a video cable which is fed into the pipe.
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Then can't you simply attach markers at known intervals along the cable?
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe something like this except resonant at 33 KHz.
    http://www.discovercircuits.com/dc-mag/Issue-1/issue-1-exciter-circuit.htm
    It would need a level shifter to get it to work with your 24 volts.
    If you know the physical size of the coil we can calculate the number of turns and the capacitor size.
     
  9. upand_at_them

    Active Member

    May 15, 2010
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    I'm not the OP, but I have seen these in use. Pipes aren't necessarily straight, level, or follow the bearing that you may think they do. Feed one of these 100 feet down a pipe inside your house and see if the dead reckoning approach even gets close.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    OK. So how close do the receiver and transmitter have to be to each other? AFAIK reliable propagation at 33 KHz. is a dicey proposition given the apparent power levels of a few milliwatts. I think 1 meter might be a stretch.
     
  11. Blangdk

    Thread Starter New Member

    Aug 21, 2014
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    Thanks for all your replies guys.

    I believe the original is approx 1 inch outer diameter, 3/4 inch inner diameter and 2/3 inch long. Is there a formula I could use to calculate it if I get my hands on one to meassure?

    You are absolutely right. They can start going along the side of a house to then make a 90 degrees bend under the house.

    The ones I have used in the past, have been able to locate anywhere from 3-10 meters. I have been lead to believe that this circuit is out of one of these transmitters.
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    OK. I see two problems.
    1. You first need to determine the inductance of the coil.
    2. There are formulas that relate the inductance to diameter, length an number of turns.
    Most inductors wound on a cylinder have an air core which results in low values of inductance.
     
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Why do you think it is the coil? Is there 33kHz drive at the gate of FET? Is FET still good?
     
  14. ronv

    AAC Fanatic!

    Nov 12, 2008
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