"Allen Mulvey" writes:
> 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

My thanks to all. These are all perfectly good ideas along with
the LM367 and the AC relay suggestion.

	I already have a couple of LM367's around and that idea
just won't go away from my head. The flasher is physically going
to be not more than 15 feet or about 5 meters from the bell
which, by the way, is the old clasic two-chime high-low solenoid
mechanism.

	If he's by himself, the speaker volume on the TV is
turned down as he listens with headphones and if there are
others in the room, one of them will hear the bell. I may take
a digital recorder over there today and get a recording of the
chime and use it as a test signal. The rooms he lives in are
amazingly quiet most of the time. The thing about LM567's is the
compromise one must make between detecting the tone quickly and
detecting it accurately.

	A fast time constant on the PLL will certainly pick up
the chime as well as any room sounds that happen to contain
enough energy at that frequency such as voices or appliance
motors, etc.

	Still, this is worth checking out.=20

	I was curious to see if one can get replacement 567's
these days and it looks like they are still available. My first
experience with one of these devices was in 1975 and I bet the 1
or 2 chips I have left are from that time period.

Maybe it's back to the future for the bell flasher.

Martin McCormick WB5AGZ
--=20
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