A relay across the switch contacts that triggers the transmitter when the
switch shorts the relay?
On Jun 13, 2015 7:03 AM, "Martin G. McCormick" <
martin@server1.shellworld.net> wrote:

>         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.
>
>         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.
>
>         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.
>
>         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.
>
>         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.
>
>         The light flashes when the base station detects that the
> handset came to life.
>
>         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.
>
>         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.
>
>         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.
>
>         I could ditch the old phone base station and use a wall
> wart to power the flasher and receiver.
>
>         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.
>
>         The only signal I need is a momentary closure or a
> momentary shot of 5 volts when the bell rings.
>
>         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.
>
>         If somebody makes a contact closure wireless relay link
> that runs on 8-24 volts AC, that's what I need.
>
>         Thank you for any and all constructive ideas.
>
> Martin McCormick
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