Subject: From: Date:

Re: [ECS] Telephone Deadman switch Dan Carrington Wed, 26 Aug 1998 09:13:25 -0700

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If the voltage stays above 8 volts under all conditions, could I use a
voltage regulator chip to output something steady like 3 volts or so to
drive a relay and use a diode between the tel line and regulator to keep
a DC input?  Would the higher ringing voltage or something blow a
regulator or overvolatage it?  Is there a type of voltage regulator that
will allow high source voltages?  How do phones keep power to themself
if they are the type that do not plug into house power?  Could I buy a
cheap $10 phone and pull parts from it?

Dan



Charles Laye wrote:
> 
> 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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