Subject: From: Date:

Re: [ECS] Telephone Deadman switch Daniel Dubay Thu, 27 Aug 1998 21:14:25 -0400

---

There's more than one way to skin a cat.  Whether you use a zener diode
or volt regulator you may need to use smaller resistors.  Since I=E/R,
the current through a 200k resistor with about 40v across it would max
out at 0.2mv.  This might be enough for a digital input but to increase
reliability and or drive a relay I would use about  a 500 to 1k
resistor.  he phone line has some resistance in series allready.  I
believe about 50 ohms.  You can test this by finding the resistor that
drops the voltage by half.

I'm not sure weather the ring voltage is AC or pulsing DC.  If it is ac
you may have to compensate for this.

Dan Dubay

<<< Charles Laye <charlie0@gte.net>  8/27  8:12p >>>
A nice resistor voltage divider should do it.  Try a 200k in series with
a 100k across the phone line and hook your regulator across the 100K.

---