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Chart Box: would this work?

  1. May 7, 2004 #1
    Hello, I am a beginning electronics hobbiest who needs a quick answer. My question is, would these plans for a "chart box" really work?

    http://www.textfiles.com/phreak/BOXES/chartreu.box

    If not, would there be other possibilities that will work? The main purpose of the chart box is too leech electricity from the telephone line and apply it to whatever you need it for.
    I don't think this will work, as the plan seems way too simple and your dealing with low voltage DC. However, I would like a professional opinion. Any insight into this is greatly appreciated. Thanks
     
  2. jcsd
  3. May 7, 2004 #2

    Cliff_J

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    This is simple conservation of energy. Power output !> power input. Dinky 24 gauge wires don't seem to lend themselves to great power transmission do they?

    Reminds me of the time I read about compromising the network of a large retail chain's computers using the handheld scanners in the stores. Since I worked at HQ I knew the equipment in question and the article was quite amusing in how far off it was from reality. Had the author actually accomplished 1/10th their objective, along the way they would have realised their mistakes in their 'theory' and found a MUCH easier method.

    Cliff
     
  4. May 7, 2004 #3

    turin

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    - The parts list smells suspicious, but perhaps I just never ran into a fuse specified for a voltage (I always dealt with fuses with current specifications).

    - It says you can get more voltage if you use a transformer, but I'm pretty sure that these lines are primarily DC, so you would need to supplement the transformer with a switcher.

    - The basic (and I do mean basic) idea behind the design is reasonable. Obviously, there is power delivered over the phone line, otherwise all phones would need to be plugged into a 120 outlet. From my experience working in the telecom industry, the voltage in the phone line is ~130 V (I'm pretty sure that's constant, though it may just be upon ring). In principle, you should be able to drive a load in parallel to the line, but as has been mentioned, I don't believe you will get much power. The description (if not the design itself) given on that web page is very sloppy.
     
    Last edited: May 7, 2004
  5. May 7, 2004 #4

    chroot

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    I'm rather sure the normal voltage supplied to a phone is 40V, and 90V on ring.

    I agree with all of the above -- you could certainly leech some power (to light the buttons on your handset, for example), but you wouldn't be able to leech much. At some point you'd blow one of the phone company's fuses.

    - Warren
     
  6. May 7, 2004 #5

    turin

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    I'm not surprised that I am mistaken. I can't remember where that 130 V figure came from; somewhere in the lab I'm sure. I definitely remember a 48 V ((ter)) ((min)) ((al)). Anyway, I think it would be a much better design to use a voltage regulator circuit, or at least a zener circuit. The rheostat would kill the output impedance (assuming it's even good to begin with, which I imagine is not true).
     
  7. May 9, 2004 #6

    Cliff_J

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    How could a fuse ever be setup to blow at a certain voltage level for protection without knowing the load or current? The lack of mentioning using something like a zener or linear regulator in the author's text tells the tale....

    Huh, I didn't know it was 90V at ring, maybe time to get out the scope and call myself! :smile:

    Cliff
     
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