"noname" wrote:


"Nico Coesel" wrote in message
...

I'm pretty sure that it won't work that simple. There are other
factors at play that make controlling things with a telephone a lot
harder to achieve than you think... For everyone's safety I'm not
going into the details.

You could, only there are no details.

piezoelectric one, since with a piezo the circuit would differ slightly. A
reed relay could do the switching. Using an NPN, the circuit would look like
this: Negative ground, connected with ringer's "-", to battery "-" and
through a forward-biased shottky to the emitter. The transistor's base
connected through a 2K2 resistor to battery "+". Base also connected to
diode "+", while diode "-" is connected to ringer "+". Collector through
relay coil to battery "+", a capacitor across the relay coil. That's it. The
relay contacts can be used to switch on a lamp, connected to the same
battery and placed so that the hearing-impaired person can easily see it.
Note to hearing-impaired preople: this circuit may not always work, it
depends on the type of ringer and on the volume setting. I did not test it
with any ringers either, but I think many old-style ones should do.

Way too complicated and it still doesn't work reliably. I've used
electronic kitchen timers -which basically have the same circuitry- in
numerous devices (Eprom erasers, etching tanks, UV exposure units,
etc, etc) but this method is too unreliable for anything that needs a
100% predictive trigger.

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