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Telephone Tip/Ring Tester Schematic

Discussion in 'Electronic Design' started by Don, Jul 12, 2003.

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  1. Don

    Don Guest

    Can anyone point me to a telephone line tester circuit on the web somewhere?
    I am looking for something that will indicate whether the line is alive and
    whether the tip and ring signals are reversed. Tried doing a Google search,
    but came up with ready, made ones. I have enough junk around here that I
    figure I can build one for nothing.

    Thanks!

    Don
     
  2. rw

    rw Guest

    if you got a multimeter and a phone you can start testing.
    check the voltage across the pair, should be 48VDC in US, 60VDC
    in europe.
    place a 600 ohm resistor, 5W across the pair and measure the current
    should be 20 to 40mA (holding current)
    rw
     
  3. the Wiz

    the Wiz Guest

    Look here:
    http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem_Tel.html

    or here:
    http://www.imagineeringezine.com/PDF-FILES/2phostat.pdf

    or here:
    http://users.pandora.be/educypedia/electronics/telephone.htm

    More about me: http://thelabwiz.home.mindspring.com/
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  4. Dbowey

    Dbowey Guest

    rw posted:
    if you got a multimeter and a phone you can start testing.
    check the voltage across the pair, should be 48VDC in US, 60VDC
    in europe.
    place a 600 ohm resistor, 5W across the pair and measure the current
    should be 20 to 40mA (holding current)
    rw-------------
    Mostly wrong........

    In the US, on many lines the Telco equipment places a nominal 52 VDC on the
    line, but many lines are served by a remote multiplexer which may put a nominal
    20 to 24 volts on the line. But the voltage may be as low as about 6 Volts
    from some pair-gain equipment.

    Use a 330 Ohm resistor to test, or use a telephone. Most modern phones are
    designed to be 330 Ohms DC. The loop current must be at least 18.5 ma.

    By the way, a tip and ring reverse will have no affect on operation of your
    phones.

    Don
     

  5. How do you distinguish between Tip and Ring?

    Harry C.
     

  6. How do you distinguish between Tip and Ring?

    Harry C.
     

  7. How do you distinguish between Tip and Ring?

    Harry C.
     
  8. In North America...
    Ring = positive = red
    Tip = negative = green
     
  9. Dbowey

    Dbowey Guest

    Harry posted:
    << How do you distinguish between Tip and Ring? >>

    ----------
    While on-hook the Ring will have a negative voltage and the Tip will be
    grounded through equipment at the Central Office UNLESS the office is a
    "Floating Battery" type office. In the latter case the Ring will have a
    negative voltage and the Tip will have a positive voltage. The sum of the two
    voltages (which are in series) will be about 48 to 52 Volts.

    Don
     
  10. The usual way of doing this is to use a bicolor LED that glows read
    with one polarity and green when the polarity is reversed. You just
    put a resistor in series to limit the current. I think the ones I
    have usre 3.3k, maybe more if the voltage is high. the max current
    for a phone line is 60 mA, so it would be wiuse to put 3 or 4 diodes
    in series in each direction to absorb any excwess current above 20 mA
    or so. But the dissipation of the resistor may be more than a half
    watt. So use a couple in series or a 1 watter.

    BTW, if you plug one of these into a wall jack, the polarity will be
    correct, but the modular line cord flips the polarity so that it's
    reversed at the phone jack. So you have to know where you're testing.

    More info is on comp.dcom.telecom.tech newsgroup.

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  11. Ross Herbert

    Ross Herbert Guest

    They must have changed it then... but somehow I doubt it. See
    http://www.elecdesign.com/Articles/Index.cfm?ArticleID=1539 and
    http://www.ktechonline.com/pdf/Telephone_Line_Measures_042600.pdf

    Anyway, if the tech reversed the main frame jumper... the wire colors
    mean nothing. You need to check the polarity with respect to earth. The
    normal polarity is;

    The 'A' leg (or TIP) is connected to earth at the exchange and therefore
    the 'B' leg (or RING) will be -ve wrt to the 'A' leg (or TIP).

    Connect a digital voltmeter between both wires of the line.
    When the meter reads -52V the red lead will be connected to the 'B' leg
    (or RING) and the black lead will be connected to the 'A' leg (or TIP).

    Ross Herbert
     
  12. And I could provide the URLs I referenced that claim otherwise.

    But I agree that it isn't very relevant anymore anyway. Seems likely
    that the contractors that work on phone wiring these days don't
    have the same attention to detail as the first couple generations
    of telephone technicians. Hard to distinguish brown with orange
    stripes from orange with brown stripes in the bottom of a dark
    manhole. :)

    And it doesn't really matter anymore anyway. All modern phone
    equipment will operate properly regardless of the polarity. The stuff
    that doesn't isn't properly designed or assembled. Note that it
    was (is?) common to reverse polarity to indicate certain things
    like call completion.
     
  13. Ahhh... wait a moment. I understand you're referring mainly to
    "modern" phones, but I still take issue with that statement!

    The older Bell System (Western Electric) phones from the 70's-
    early 90's are most certainly "properly designed and assembled" (as
    evidenced by their amazing service life -- my key system has been going,
    more or less continuously, for 20+ years), but earlier TouchTone sets
    will not dial out with reversed polarity.

    In fact, it was common practice among telephone installers to flip
    the polarity on the connection to sets that the owner did not want
    people to be able to dial out on.
    I've not heard of RP being used to indicate call completion
    (perhaps someone else has?), but I will say that it is common for most
    central offices in the U.S. to drop the line battery altogether for
    about two seconds, if a phone goes off-hook and you don't do anything
    for 30 or so seconds.

    The reason for this dates back to the first key telephone systems,
    developed in the 40's. If a line were taken off-hook, and then
    immediately put on hold, or if a caller on hold hung up and the line
    went back to a dial tone state, AND the hold bridge failed to release,
    it could tie up common equipment at the CO.

    That battery drop I mentioned above will force the hold bridge at
    the customer's end to release, thus clearing the line. Even the most
    modern of electronic CO's do the battery drop thing to this day.

    This has been your Bell System trivia for today. We now return to
    your regularly scheduled Schickelgruber.
     
  14. Dbowey

    Dbowey Guest

    Anton posted, in part: "I've not heard of RP being used to indicate call
    completion (perhaps someone else has?)"

    Reverse polarity is used in "Loop, Reverse Battery" Trunk Circuits. Phone
    lines do not use RP.

    Don
     
  15. "Dr. Anton Squeegee" wrote ...
    But as time went on, apparently it got harder to find good help.
    So it became cheaper to put a 50-cent bridge rectifier in the
    dialpad circuit (which they actually did), than to pay the tech to
    debug why the old phone worked and the new one didn't.

    Yes, I was assuming that >99% of the readers of this thread will
    not have access to polarity-sensitive, early TouchTone equipment.
     
  16. Dave VanHorn

    Dave VanHorn Guest

    When they converted the Waikiki exchange to ESS, half the subscribers lost
    the ability to dial.
    Seems there were a lot of reversed reversals in the middle of the wiring,
    and the installers just flipped the leads till it worked. :)

    Even into the 80's I had no true DTMF service, though the telco charged for
    it.
    They put a tone to pulse converter on each line. "Beep"-Dit-Dit-Dit...

    This was also a time when you couldn't dial 800 numbers from hawaii.
    Most frustrating when some companies had ads with only 800 numbers on them.
     
  17. They had to pay for all those individual line tone->pulse
    converters!

    Same in the Redlands (CA) exchange. As late as the mid-70s the DDD (Direct
    Distance Dialing) was implemented in Strowger relays. (Reputed to be the
    first DDD in the General Telephone territories.)

    You could dial San Bernardino (opposite side of the freeway) and wait for 5
    minutes of "tick-tick-tick-tick...". Or just call the Operator and tell her
    you call didn't go through. Some of us didn't even bother to try dialing
    first.
     
  18. Been there, done that, got the T-shirt. Damn installers ruined a
    lotta times and I get stuck with straightening out their abortions.
    I had pulse dial, and got my 300 baud Smartmodem, with DTMF. I used
    the TT on it once, and the Pac Hell bastards tried to contact me and
    make me pay for the service. They wanmted a buck twenty a month!!
    For something that benefitted them more than the customer! Finally
    the Calif PUC came to their senses and made the telcos give everyone
    DTMF for free, so we could all call the 'voice jail' systems without
    having to switch from pulse to tone after making each call.
    Yeah, lotta good that does the customer. Like when your number is
    998-7999.

    I had a Rat Shack TRS-80 Model 100 with the modem that dialed at 20
    PPS, and it worked okay, too. Twice as fast as regular pulse. I
    believe it still would work today, too.

    [snip]


    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
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    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
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    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  19. I worked at LLU from 69 and moved to OR in 78. Back then, they still had
    9-10 operators with cord sets handling incoming calls (no direct inward
    dialing). And the campus system was switched in a large room full of
    Strowgers and twenty-four 2v wet cells the size of refrigerators.

    Heard that after I left LLU became so peeved with the Redlands CO (GTE) that
    they put up a private microwave and got service from across the freeway
    (Colton, PacBell).
     
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