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Circuit design for phone strobe light alerting system

Discussion in 'Electronic Design' started by Blair, Jan 17, 2007.

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  1. Blair

    Blair Guest

    I have a mom who is hard of hearing and I have seen all over the web
    phone strobe light alerting devices. Essentailly these units are
    powered by the phone line and a ligh bulb flashes every time the phone
    rings alerting the person that the phone is ringing. Does anyone have a
    cicruit design for this I can have/buy.
    I would imagine these are not terribly hard to make...if only I had the
    design :)
    Any help would be greatly appreciated.
    Thank you very much,

  2. D from BC

    D from BC Guest

    I don't know hopefully other posters can fill in the

    I know a ring off a telephone line is a large voltage.
    But I don't know the waveform or how much it can be loaded.
    But I do know very bright LED's can substitute for a strobe....
    But I don't know how many can be used...

    D from BC
  3. default

    default Guest

    You are sitting on one of the great research tools around - did you
    search for it? Lot of schematics on the net.

    This is Usenet, not Google Groups, before you post, you look for the
    information yourself, "Groper."
  4. Guest

    I've used neon bulbs attached directly across the incoming phone line.
    Radio Shack or your local equivalent probably stocks them.

  5. mpm

    mpm Guest

    Not hard to make, but why do it?
    It will probably end up costing you more money.
    I would suggest buying one, take it apart, tinker with it, etc.. get
    the education, and then gift-wrap it?

    You will solve at least the following problem issues: --which you did
    not mention.

    1 - FCC Part-68 Registration issues (legal & technical requirement for
    devices intended to be connected to the public switch telephone
    network). I assume you are in the US, if not, other countries have
    similar requirements.

    2 - Safety. (Think lightning strike, here.) Ring voltage (US) can be
    90-volts DC nominal, sometimes much higher.

    3 - Reliability. OK, this one might be a reach depending on what you
    might buy. I don't mean to imply your design would be inferior, but I
    think we can all agree it would be re-inventing the wheel. A wheel
    that has literally been beat to death....

    That said, I don't know a single elect. hardware design engineer who
    hasn't taken a phone apart at some point!! Enjoy!
  6. default

    default Guest

    Neon bulb would work if you are looking directly at it, not too useful

    Ring voltage is something like 90 VAC 30 HZ. With a cap, rectifier,
    zener, small filter it is easy to just put the limited DC into a solid
    state relay or optical coupler.

    Or buy one ready made phone line flasher at Electronic Goldmine for
    $5. receptacle switches 120 VAC lamp
  7. But then you use the light from the neon bulb to turn on a photelectric
    device, which controls the light flasher.

    Or, you get a modem, and power it up (easiest if it's an external modem),
    and then use the ring detector circuitry from there to control a flasher.

  8. default

    default Guest

    That's doing things the hard way . . . build an optical isolator
    around a neon bulb (LED, cds photocell, triac and some potting
    resin. I used to do that before solid state relays came along) It
    could be done, but why would you want to?
    Modem? Let me guess, you really, really, like Rube Goldberg?

    You'll love this: take a laser pointer and power it from the ring
    voltage and use mirrors or optic fiber to send it around the house.
    Or how about a mechanical gate that drops a ball into a tube, the ball
    winds its way through the house tripping mechanical flags, and setting
    several wind up mechanical toys into motion, . . . . Has a simple schematic,
    except U1 and everything West of it could be replaced with a single
    solid state relay, and eliminate the transistor and DC supply. Still
    cheaper to buy it ready made though . . .
  9. jasen

    jasen Guest

    50-100V low frequency (no more than 20Hz).
    sine with a 48V DC offset.
    not a whole lot, but then a xenon strobe doesn't use much power,

    start with a mains strobe bulb add a few Cockroft-Walton stages to rectifier.

    If low-visibilty is acceptable use an off-the shelf 110V rated neon indicator.

  10. jasen

    jasen Guest

    yeah, pin 9 (or 22 for 25 pin ports) goes to -12Vish when the phone rings.

    that could switch on a p-channel mosfet, pnp transistor, or optocoupler
    but there's not quite enogh drive to operate a small relay.

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