adsl filter with L.E.D indicator

Discussion in 'The Projects Forum' started by rnbguy, Dec 11, 2011.

  1. rnbguy

    Thread Starter Member

    Oct 8, 2008
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    Hi All,
    I have a question, I am trying to build an adsl filter or passive device, which contains an L.E.D indicator if ADSL frequencies are detected on the line.
    The device does not need to handshake or anything, just detect dsl frequencies (not just voltages)?

    Am i asking for something from the future or is this possible given what we have today?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    It is very possible, though I am weak on how to do it. You would need a external power supply, no taking power from the phone company to power this. Probably a simple high pass filter (like a DSL filter) with a signal detector would do it.
     
  3. rnbguy

    Thread Starter Member

    Oct 8, 2008
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    Hi there, thanks for the reply, thats actually light at the end of the tunnel.

    the part im stuck on is, what can be used as the signal detector component?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    An amplifier with a diode detector. The diode detector will convert the AC that is the signal into DC voltage, which could trigger a circuit that will light the LED.

    Like I said, I'm weak on DSL theory (though I had DLS once). I am making a basic assumption that their is a DSL carrier wave. I feel comfortable making this assumption, but I've been wrong before.

    Ever do any breadboarding or electronics?
     
  5. rnbguy

    Thread Starter Member

    Oct 8, 2008
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    the issue i see with that, is there are always voltages on the line, regardless if dsl is present or not.

    so converting and amplifying the ac signals to dc to power up a led could be testing the wrong thing
     
  6. rnbguy

    Thread Starter Member

    Oct 8, 2008
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    what if i use a frequency to voltage converter which will generate a certain voltage based on frequency input, this can be followed by an L.E.D which is powered on once a certain voltage is applied (meaning the input frequency at the converter is high enough to be adsl frequencies)..?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Want me to draw a schematic? No guarentees it will work, but I'm always telling people a schematic is worth a thousand words.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    A DSL filter is a low-pass filter used in series with each phone to block the DSL signal and prevent noise in the phones from interaction of the DSL signal with the phone electronics.

    The DSL carrier is around one MHz so an RC high pass filter of about 500kHz with a 1MHz amplifier may allow detection of the DSL signal. Rectify that signal to give DC which can drive a DC amplifier to light the LED.

    I think the signal is quite small so you may need a fair amount of AC gain to detect the signal. Circuit and line noise could be a problem.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    I know what the DSL filter is, I wasn't aware of the 1Mhz signal though.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Well, you said to use a "simple high pass filter (like a DSL filter)" whereas a DSL filter is a low pass filter.:rolleyes:
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    Actually it is both. The low pass side goes to the phone, the high pass side goes to the modem.
     
  12. t06afre

    AAC Fanatic!

    May 11, 2009
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    If I understand your question correct. You are going to use the phone line as power for this. Not sure how smart this is.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    Reread post #2.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    The confusion is that we are apparently talking about two different types of DSL filters. The ones I've seen are connected in series with the phones and have one input and one (low-pass) output. There is no filter in the line going to the modem.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    I've had DSL (FIOS now), the modem had the type of filter I described.

    http://en.wikipedia.org/wiki/DSL_filter

    A phone only needs the low pass filter as you describe.

    I prefer my FIOS, since the router is part of the system. With DSL I had to provide my own. FIOS is supposed to be much faster, but I have trouble telling the difference due to my old slow computer.

    My base assumption is the DSL side of the main filter is only the high frequencies, which is what I assume the OP is needing to use.

    If I were to design a detector I would use Schottky diode due to their low voltage drops and make a simple AC/DC converter, feeding the results into a simple comparator. If the signal strength were too low I'd think about putting an amplifier in front to boost the signal. Normally I would use an op amp, but it sounds like the frequency is too high, so a transistor version it is.
     
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