Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request
From: toddi@gtisqr.UUCP (Todd Inch)
Newsgroups: comp.dcom.telecom
Subject: Need a Light to Indicate Phone *Has Rung* (Not *is Ringing*)
Message-ID: <1914@accuvax.nwu.edu>
Date: 6 Dec 89 18:46:41 GMT
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Reply-To: toddi@gtisqr.UUCP (Todd Inch)
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I want to reply to the person who wanted a light to tell him if the
phone rang (and therefore he probably has voice mail) while he was
away.  (Sorry, I lost the original article, please forgive my vague
reference.)

About a week ago I submitted an article on how to make your phone bell
into a ringer.  If you do that, or use some other relay-type device,
it should be easy to make the lamp stay on with the following circuit.

Get a relay which will operate on the same voltage as the lamp you
want to power.  A common normally-open single-pole single-throw type
will probably do (see note at end.)

Connect the contacts of the ringer-relay (operated by the phone
ringing), the power supply (or possibly battery if you use an LED),
and the coil of the new relay in a series circuit.  Now the first
relay will operate the second relay when the phone rings.

Now connect the contacts of the second relay across (in parallel with)
the contacts of the first relay.  This allows the second relay to
"turn itself on" and the ringer-relay can also still turn it on.  When
a pulse through the ringer-relay operates the second relay, the second
relay will keep itself on after the pulses have stopped.  This is a
simple latch which I've also used for burgalar alarms.

Connect the lamp in parallel with the coil of the second relay so it
is also turned on and kept on.

Install a normally closed (normally "on") switch in series with the
power to the circuit (or just an on-off power switch.)  This will
reset the second relay and lamp by momentarily disconnecting the
power.

It may be necessary to add a diode (rated between 1 and 15 amp and at
least twice whatever voltage you're using) in parallel with the second
relay coil and the lamp.  Be sure the Cathode (striped end) is
connected to the Positive side of the coil and the Anode is connected
to the Negative side, which is backwards from the way they are usually
connected.  This will effectively stretch the pulses by using the
coil's inductance to keep its current flowing after the pulses have
stopped.  This is assuming you're using DC power.

If you do have a second pair of contacts in the relay, I'd use those
for the lamp circuit, disconnecting the lamp from the relay coil.
This may be necessary if the lamp draws lots of current.

If you use an LED (light emitting diode) with a series 220 ohm to 2K
ohm resistor (depending on the voltage) as the indicator lamp, you
shouldn't need the diode across the coil and you won't need to worry
about the lamp current draw.

Also - regarding my previous suggestion for turning a WECO-type bell
into a ringer-relay, you MAY be able to place the reed switch in the
right spot on the frame or near the magnet or somewhere so that the
ringer is still intact (and therefore rings) but also operates the
reed switch, although I haven't tried it.  The switch may provide
pulses which are too short if the magnetic field at that location is
too weak.

I hope I haven't made this sound too complicated, it really isn't, but
let me know if you want more info.  Hope this helps.

 
Todd Inch, System Manager, Global Technology, Mukilteo WA  (206) 742-9111
UUCP: {smart-host}!gtisqr!toddi    ARPA: gtisqr!toddi@beaver.cs.washington.edu
"You are the booger in the nose of my life." - My wife, to me. (Jokingly?)
Disclaimer:  My boss will read this while checking up on me and will disagree.