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How do Cable Tone Generator/Tracers work?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by johankj, Nov 13, 2007.

  1. johankj

    johankj New Member

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    I'm looking into buying one of these, but I want to find out how hard it would be to make one. Besides, if I make it myself, I can customise it to my needs...

    The signal generator itself should be simple. I have a few MAX232 chips lying around, so I though I'd just use one of them to generate a 900Hz/1000Hz 10Vpp-20Vpp tone.

    But I'm not sure how to pick up that signal with an induction type probe (Which I assume they are)? I'm not expert on radio stuff, and I have not experimented with induction, fields, and electromagnetic waves much...

    Does anyone have any suggestions to how these are constructed?
     
  2. Leftyretro

    Leftyretro New Member

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    Hi J;

    I use to use them at work tracing wire pairs in long 50 pair cable runs. They worked very well. I think we called them the Fox and Hound (you might try a google search on that term) as that might have been their marketed brand name or model. Anyway the sender had to be electrically attached to the wire (using ground) or to a pair of wires with clip on connectors. The receiver did indeed use a magnetic induction probe. You could pick up the tone when close to the wire bundle and it would get louder when held right on the insulation of the correct wire or pair.

    Not sure of construction details but the tone was a pulsed tone and I'm sure the induction coil pick-up was tuned to match the frequency of the signal generator.

    This sure saved a lot of time and trouble searching for unmarked spare pairs in long instrumentation cables that sometimes went for 1,000s of feet.

    Lefty
     
  3. johankj

    johankj New Member

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    I'm thinking this will save me a bunch of time too. I do run allot of signal-wire at work, so finding the right one without having to trace it would be a time-saver.

    I'm pretty sure the tone generator just emits a 10V (peak-to-peak) square wave, so that should be fairly easy to construct. But I know very little, at least practical know-how, about inductors and coils and such. :(

    I'll google 'Fox and Hound', see if I can find some circuitry. Thanks for the input Lefty, much appreciated..:)
     
  4. dave

    Dave New Member

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  5. johankj

    johankj New Member

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  6. Super_voip

    Super_voip New Member

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    The MAX232 is a great idea, normally it is just 9V pulsed. The receiver isn't tuned to the frequency rather it has a low pass filter on a high impedence amp. Best way to use them, to find a cable, is to use seperate wires in the cable not a twisted pair. The twisted pair is designed not to let signal interfere with others. To find a pair in a cable connect to the pair.
     
  7. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Cable and pipe tracer.

    I needed to build one in an evening to track the water pipe and 110 volt wires going from the house to the well. With no water time was critical. (make it simple)

    The receiver: Use an AM portable radio.

    The transmitter: 9 volt battery, LM78L05 voltage regulator, 1000pf 500 volt capacitor, two alligator clips, crystal, and 74HC4060 osc/counter. The 500 volt capacitor blocks DC and 60hz AC from coming into the output stage. I chose a crystal frequency with a harmonic in a quite place on the radio dial. The 74HC4060 has many Q-outputs. One of the outputs had an approximately 2khz tone. Using a simple OR circuit I summed the CLK2 and 2khz together. The output was a square wave with a harmonic at 1mhz, turned on/off by a 2khz square wave.

    To use:
    (ground lead from transmitter) Connect one alligator clip to ground, or your metal tool box, or a 2 foot piece of wire. Almost any thing.
    (signal lead with DC blocking capacitor) Connect one alligator clip to the wire or pipe you want to trace.
    Wave the radio near the wire/pipe. Twist the radio around. Most AM radios are more sentient in one direction.

    I followed a, 5 foot, buried wire 50 feet. At the house I could hold the radio and walk. At 50 feet I had to set the radio on the round to detect the wire.
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Love it! :D
     
  9. johankj

    johankj New Member

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    The fact that they twist does this, if I remember my electromagnetics correctly (Dreaded right-hand rule of vector mathematics). I didn't think about the fact that that has an impact on the ability to trace pairs. I guess one wire from two pairs, or two pairs tied together would work...

    Thanks for the tip. :)
     
  10. johankj

    johankj New Member

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    Hehehe, cool! :D Proper McGyver DIY!! If I understand your description correctly, you get a 2KHz signal amplitude modulated onto a 1MHz carrier? Ground it and connect the output to what you want to trace? Do you take the output directly from the crystal?
     
  11. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    http://www.electro-tech-online.com/custompdfs/2007/11/MC74HC4060A-DPDF.pdf
    Go to page 7, see Crystal Osc Circuit.
    Pin 11 is about ½ supply with little ripple.
    Pin 10 is square wave with rounded edges.
    Pin 9 is square wave with sharp edges and plenty of harmonics. (use pin 9)

    Reset pin 12 = gnd

    I just looked in my low frequency XTAL bin and found sever at 1mhz and some near 1mhz. In my resonator bin there are many from 100khz through 307khz. Any will work.

    I was reverse engineering a wire tracer and realized that the receiver was a simple 455khz radio receiver. Why not an AM radio? The transmitter could be any oscillator that will put energy into the AM band. (modulated by an audio tone)
     
  12. johankj

    johankj New Member

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    Ah, I see. :) Thats pretty clever :D However, I don't own an AM-radio :( We've pretty much migrated to DAB here in Norway. I'll see if I can find one somewhere, though...
     
  13. Super_voip

    Super_voip New Member

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    DAB, your lucky, the cheapest DAB here is around $250 and the phase out for AM isn't for years.
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    DAB! - it started in the UK and was developed here, but coverage is useless and quality isn't as good as FM radio, and some channels are only in mono!.
     
  15. johankj

    johankj New Member

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    It's supposed to phase out FM in the next two years, however, I think there is plans to keep the world long-range AM service.

    There has been some criticism of the move to DAB, as each channel has relatively low bit-rate/bandwidht, and with no real way of upgrading the transmission without making exciting DAB-radios incompatible. I think the bit-rate is 128kbps. In general, the reception is good, and the persived quality is also good, better than FM-radio.

    Norway is also moving towards digital terrestrial TV, with the first official broadcasts strarting just a few months ago. Here, at least, we got something right, and opted for MPEG4 compression rather than MPEG2. The selection of channels is rather poor, compared to UKs digital TV.
     
  16. Super_voip

    Super_voip New Member

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    Ahh, there at least we're doing something and we are going digital TV at a very fast rate.We have 4 settop boxs already. Goes to show how well the DAB is going here I don't know if it's replacing AM or FM, I'm sure it's AM.
     
  17. johankj

    johankj New Member

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    In Norway, it's replacing FM. I see you're an aussie, so I don't know if your large country may have adopted a different scheme radio wise...
     
  18. Super_voip

    Super_voip New Member

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    Any way there was a little project in Elektor a few years ago that had the circuit for sender and pickup. I have 3 cable tracers at work so I don't really need anymore. One thing I was going to do was use PIC or 89c2051(have many) to make a PWM with at least three tone output, I sometimes get the two tone ones confused with other signals. I like the MAX232 idea for signal boosting.
     
  19. Super_voip

    Super_voip New Member

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    Just checked on our Communicatins department web site and it seems trials are still underway, so it may be DRB(DAB) or DRM yet.
     
  20. johankj

    johankj New Member

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    Elektor is great, it's such a varied hobbyist electronics magasine. I like the fact that they tend to use pics.

    I ended up buying an inductive probe on Ebay, and it came with three tone generators (BNC, RJ45, clips+RJ11). I bought it mainly for the probe, which with the housing and all, I doubt I can make better. I may still make a tone generator thought. I had an idea, because I trace allot of CAT5/6/7 wire, that I'd do a tone generator that had a different 'beat' for each pair (or similar), like morse code... I don't stock any hig-end pics, so mine only have one PWM in general, but I may still be able to make something of it... Tones in the KHz range are not to difficult to produce anyway, I could even 'demultiplex' the signal somehow...
     
  21. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Unfortunately though they almost always don't release the code, requiring you to buy it from them!.

    EPE is far better, even more PIC articles, and the software is always a free download.
     

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