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 Telephone bug during ring

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enodo Posted - Feb 12 2009 : 12:02:03 PM
Looking at the schematic for the telephone bug, I don't see why it doesn't get fried when the phone rings and there is 90 VAC across the IN lines. What am I missing? Does it have to be taken offline when the phone rings?
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enodo Posted - Feb 15 2009 : 10:23:30 PM
Not sure I get it. If you add a resistor in series with the LED, how will it act as a voltage regulator? If the resistance is 300 ohms, and this is in series with the phone's ringer, will it still ring?
audioguru Posted - Feb 12 2009 : 12:25:47 PM
The circuit uses a red LED as a 2V voltage regulator.
The circuit is connected in series with a telephone, not directly across the telephone line so the ringer in the telephone gets the ringing voltage minus 2V.
The text says to add a resistor in parallel with the LED if the LED burns out.

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