If it is an old solenoid device, how about one of these
simple solutions:
1) a micro switch on the armature to detect its motion
2) a reed switch or hall effect device to detect the
magnetic field of the solenoid

Allen

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-
> bounces@mit.edu] On Behalf Of Martin G. McCormick
> Sent: Saturday, June 13, 2015 9:01 AM
> To: Microcontroller discussion list - Public.
> Subject: [OT] 16-volt AC Wireless Contact Closure Device
>=20
> 	About a year ago, I built a wireless flashing door
bell
> alert so my father could tell when somebody rang the bell
> while
> he had headphones on while watching TV.
>=20
> 	It worked fine but he is moving to a retirement
> community where the bell is physically different enough
that
> my
> circuit won't work there.
>=20
> 	On the old circuit, I had a current-limited
optoisolater
> at the output of a full-wave bridge
> monitoring the signal across the chime which was a dirty
60-HZ
> pulse normally and changed to 120 HZ when the button was
> pressed.
>=20
> 	The 12F675 then asserted 5 volts on Pin 5 which went
> through a transistor sending power to an old 80's-vintage
> cordless phone handset.
>=20
> 	The phone base station is used as the receiver and
also
> a power supply for the red flasher which is another
PIC12F675
> whose output pulses the base on a transistor that flashes
a
> 12-volt LED light 5 times per second.
>=20
> 	The light flashes when the base station detects that
> the
> handset came to life.
>=20
> 	In his new digs, the bell is an older-style
> electromechanical chime which would be no problem except
> that I
> don't have access to both sides of the bell transformer
for
> power there and the physical space is also smaller.
>=20
> 	A garage door opener would be perfect except I would
> need to pop open the transmitter, solder the button
contacts
> closed and then find somewhere to stuff a diode bridge,
> capacitor and regulator.
>=20
> 	If somebody already makes such a wireless relay
link, I
> would be a happy camper. If it was small enough, it could
> probably fit inside the chime.
>=20
> 	I could ditch the old phone base station and use a
wall
> wart to power the flasher and receiver.
>=20
> 	If it turned out that the receiver is portable, it
is
> likely I could work around that as there is more physical
space
> on the flasher box.
>=20
> 	The only signal I need is a momentary closure or a
> momentary shot of 5 volts when the bell rings.
>=20
> 	I even briefly entertained the thought of a
microphone
> and audio decoder circuit to "hear" the bell but it would
be
> easy to confuse and might false trigger from many sources.
>=20
> 	If somebody makes a contact closure wireless relay
> link
> that runs on 8-24 volts AC, that's what I need.
>=20
> 	Thank you for any and all constructive ideas.
>=20
> Martin McCormick
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--=20
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