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- Oct 8, 2001
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I need to know how to make a fixed-line phone ring (without calling it) for an April Fool's Day prank. Any ideas?
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Diggrr said:http://wandel.ca/homepage/phonering.html
If you have the $135 for the joke, there's the tele-q, made to make stage prop phones ring on cue.
It's a tough signal to duplicate, because a phone uses DC for dialtone, and AC for ring impulse.
OK, now take out your pocket protector and let’s get technical…
The POTS phone line, with all phones on-hook, should measure around 48 volts DC. Taking a phone off-hook creates a DC signal path across the pair, which is detected as loop current back at the central office. This drops the voltage measured at the phone down to about 3 to 9 volts. An off-hook telephone typically draws about 15 to 20 milliamps of DC current to operate, at a DC resistance around 180 ohms. The remaining voltage drop occurs over the copper wire path and over the telephone company circuits. These circuits provide from 200 to 400 ohms of series resistance to protect from short circuits and decouple the audio signals.
To ring your telephone, the phone company momentarily applies a 90 VRMS, 20 Hz AC signal to the line. Even with a thousand ohms of line resistance, this can still pack a bit of a shock so be careful when you are probing around trying to find a POTS line.
JigPu said:
OK, so the phone has 48VDC on it normally (that is, 48VDC between the two wires running to it). When a ring is sent, that signal changes to a 90VAC @ 20Hz. All you have to do is find some way to send a 20Hz signal down your wire at "only" 90V (and then switch back to 48VDC)
JigPu
Diggrr said:Still harder than you thought it might be, eh?
Damn... 4 year old thread... and the best solution lands in it... LOL
Damn... 4 year old thread... and the best solution lands in it... LOL
Its 2010? Crap.