Connect with us

telephone current

Discussion in 'Electronic Basics' started by Michael Hamm, Aug 12, 2004.

Scroll to continue with content
  1. Michael Hamm

    Michael Hamm Guest

  2. Take a phone cord (CAT11), plug one end into the wall, strip off the other end so you get the bare stick em in your mouth! Really, that's the best way you can use it. And oh hey, if you
    get someone to call your house while you're doing it, you should also get a lovely spike, about like
    40 volts if I remember correctly, that's even better than the base 12 or so volts...not really much
    of a phreaker though so I can't say for certain, but putting the wire in your mouth, yeah, I think
    that'd be the easiest way for you to find what you're lookin for. ^_^
  3. Meat-->Plow

    Meat-->Plow Guest

    Shut up Diaper Boi, we don't care what you think.
  4. When on-hook, you really cannot get much power from the phone line. A very few
    microamps (load on the line should be something like 5Meg or greater.) There
    was a time (like on the princess phones) when the phone company actually
    supplied a power wire-pair for the phone lights. But that didn't last so long.
    If there was any appreciable power availability from the phone line, can you
    imagine how much power they might have to fund without anyone to charge for it?

    When off-hook, they are supplying power. So you can draw some current when you
    are engaged in a phone call. But the total loading (including the phone you are
    using) shouldn't go under some hundreds of ohms at a subscriber site, if I
    That's a wide-open question. You should have clarified it by providing some of
    the specific ideas you are thinking about. How can anyone well answer such a
    question as you ask here?

    The general answer is that you shouldn't consider it. Dbowey is an expert on
    this subject, sometimes posts here, and was a real help in letting me know just
    how difficult even this task really is, if it is to be done well and correctly.

    I wanted an LED indicator that wasn't part of any phone and that I could put on
    every phone jack in the house to provide a positive indication if the line was
    in use. My resulting circuit draws less than 1uA of current when the phone is
    on-hook and draws just 1mA for the LED when the phone line is off-hook. Even
    then, I can't add too many of these around the home as the LED draw itself could
    wind up "holding" the line after the phone is replaced to the on-hook condition.

    I considered the idea of automatically interrupting the LED load every so often
    so that I could test the line, allowing a larger number of these to be used
    simultaneously, but I'd need to include time for the central office to respond
    and I'd need to work out some way for all the LED units to remove their loads in
    concert with each other, too. Way too much pain.

    The phone system has been carefully crafted over time exactly for one purpose
    and probably also to minimize their operational costs due to problems or abuse
    at the subscriber end of things. They've got it pretty well cornered, now.

  5. Michael  Hamm

    Michael Hamm Guest

    Actually, I'd been thinking of wiring up a lightbulb during a blackout.
    Someone else noted that it's likely illegal and/or against the TOS/AUP.
    So I won't. But based on responses, I suppose I *could* if the phone is
    off the hook. I'm a tyro: I don't know when the phone is "off the hook":
    but it seems to me that if I (somehow) attach a lightbulb to my phone wire
    and plug the latter into my jack, the phone company will consider me "off
    the hook", no?

    Michael Hamm
    AM, Math, Wash. U. St. Louis
    Standard disclaimers: ... legal.html
  6. John Fields

    John Fields Guest

  7. andy

    andy Guest

    but if you use it for anything other than powering telephone equipment in
    a way approved by your telco, you're probably breaking the law / terms of
  8. Nope. Maybe an LED. But also, the phone company will (I believe) sense a
    current draw where you DO NOT make a phone call as a "customer problem" and
    disconnect you, periodically and automatically rechecking the line every so
    often. They don't like supplying power, unless it is for a phone call.

    But no light bulbs. Not even close.

  9. Jamie

    Jamie Guest

    apox 50 volts when waiting.
    100 when ringing.
    around 10..15 when the phone is off the hook.
    the polarity will alternate depending on if the other party
    picks up on the other end, this is one way how automative
    equipment knows you answered the phone.
  10. Roy McCammon

    Roy McCammon Guest

    they'll consider you "perminant signal" and disconnect you for a while.
  11. "Off Hook" means "while the phone is in use". If you draw any
    appreciable current from the phone line (even just a couple of mA to
    light a LED), the phone company will think your phone is "off hook",
    and anyone trying to call you will get a busy signal. If they see
    that your phone is "off hook" for a long time, without your making a
    phone call, they will disable your line, and/or initiate
    troubleshooting procedures.

    Even if you are willing to accept these problems, you can only draw a
    few mA - perhaps enough to light a couple of LEDs - certainly not
    enough to produce any useful room lighting.
  12. Rich Grise

    Rich Grise Guest

    Have you ever left an actual phone sitting off-hook? After awhile,
    the dialtone stops. Then, after maybe 10 minutes, it starts an
    alarm that you can hear all the way across the room - I wouldn't
    want to be across the lines when that happens - and then they cut
    it off.

    Or at least they did mumble-mumble years ago. :)

  13. Externet

    Externet Guest

    There is about 0.2 Watts available. At about 6V and 35mA average,
    depending on the distance from the Telco.

    I have a transistor radio with a small power adaptation circuit and
    works very well into the telephone line. To use as illumination, a 6V
    0.03A light bulb is the most you can get, or 6 leds in 3series
    2parallel, each running with 2V at 15mA.
    The ringing signal has 1W per REN number. If your line has a
    capability of 5 REN; then 5W every time the bell rings, at about 86V
    at 20 Hz depending on your country.
    1 REN is 8000 ohms impedance.

  14. In my area, it's about 8V @ 24mA with a 330 Ohm resistor hung across ring and
    tip. Of course, this means the phone line is considered "off hook" and I won't
    be getting any calls (or making any.)
    I've run LEDs on the phone line. But, at least in my area, the phone company
    cuts off the power for periods of time if there isn't an active phone call in
    progress, reconnecting some power occasionally to see if the problem has removed
    itself. The phone company doesn't know if some squirrel has just shorted the
    phone lines or not, when you draw power, and they don't appear to want to just
    keeping feeding power down the line if it isn't working right.

    Regardless, drawing in the range of 10mA means your phone circuit isn't
    available for phone calls. It busy's you out.

  15. That's close to what I get as well (off hook of course). On hook gives me
    close to 50V and I can draw roughly 3mA from it without the CO cutting me
    off, or missing any incoming calls. ;-) I've run a PIC chip and an LCD
    powered solely by the phone line for days on end without any ill effects.
  16. I found some information I'd written down in notes, somewhere:

    On-Hook: 53V typical, only 5M loading allowed, can rise to 100V
    Off-Hook: 3V-9V spec'd, 20mA marginal, 23mA minimum

  17. One thing I've seen done is to charge up a big capacitor with a small
    current that won't cause the telco to think you are off hook. You can
    then do things like power intermittent sensors using the accumulated
    charge across the capacitor. When the sensor detects whatever its
    programmed to detect, it then makes a phone call to report the
    situation. The circuit requires no external power source, other than
    the phone line.

    Bob Monsen
  18. Anthony Fremont said
    This is peaking my interest for no particular reason. What would one do
    with such a processor and display connected to the phone line?
  19. andy

    andy Guest

    you mean politicians are there to stop all the shit falling on the
  20. John Fields

    John Fields Guest

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day