- Jan 1, 1970
Thanks for your reply.
Unfortunately, your solution, while interesting, misses one of the
requirements of the whole deal: it needs to operate the
bell/chime/annunciator *momentarily*, not continuously.
Since you need 18-24vdc, instead of the hazard of components
directly connected to the powerline, use an approved AC adapter or
"wallwart" that would provide the necessary DC voltage. From the
output of the AC adapter, place a PTC (positive temperature
coefficient) thermistor in series with your load. It will be a bit
tricky to determine the right physical size and nominal resistance of
the thermistor, since you haven't specified the load.
When the adapter powers up, the thermistor will be cold, and will
run the "indicator" what ever that is. After the thermistor heats up,
it will reduce the current going to your device, hopefully to the
point where it won't be noticed. The "resetable fuses" work on this
idea, you could use one of them the same way, but you need to again
select based on current load, and power.
If you get it to work it's: simple
doesn't violate electrical safety
The disadvantage, is that once on, it needs some time to "reset"
(cool down). The thermistor does get hot, a poorly designed circuit
could get hot enough to be a problem.
There are relay circuits that do much the same, but I'd run them
off the ac adapter as well. (relay in series with large cap, operates
when cap charges up. cap was bleeder resistor in parallel so it
discharges prperly when power is removed). The relay circuit would be
straight forward to calculate the on time (a percentage of the time
I'd prefer you stick to quite low voltages (6-12v), to minimize any
risk of shock. Who knows how this circuit might be physically