Subject: From: Date:

Re: [ECS] Telephone Deadman switch Daniel Dubay Wed, 26 Aug 1998 20:14:11 -0400

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Hello Dan,

The critical spec for a voltage regulator is the power dissipation. 
This is calculated as the voltage drop across it times the current
through it.  The voltage drop may be high at ~60Volts but the current
drain of a relay is only 10-20 milliamps.  So you might have up to a
Watt of power.  I don't know if this would affect phone function though?
 Transistors have much lower power drain.

Dan Dubay

>>> Dan Carrington <dc_grafx@microworks.net> 08/26 12:13 PM >>>
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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