Subject: From: Date:

Re: [ECS] Telephone Deadman switch Charles Laye Wed, 26 Aug 1998 12:04:59 -0400

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The phone lines have 48-52 volts DC on them at idle,  ringing is about
90v AC at 20 hz, unless you have special ringing.  Pick up a phone ant
the voltage drops to 8-12 v DC.  You could hang a relay across the phone
line, but it would drop out when you picked the line up or use a ADC
and  watch for the three conditions.  Remember ringing is ac so you will
need a diode in line with your adc.  Hope this helps. cl

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