Electronics Forum / Basics / January 2006

I've built a 418MHz RF receiver into a Radio Shack project box together
with a couple of relays.  When I push one of the button on the
transmitter, one of the relays closes.

My intent is to wire this into the doorbell circuit, so I can ring the
doorbell remotely, when no one is there.  I can then use this to
desensitize the dog to the doorbell - teach him to not get so excited
every time he hears it ring.

I have a clip for a 9V battery inside the box, but I also included a set
of binding posts so that I could power it from an external source.  I'd
thought that I might be able to power it from the doorbell circuit.  But
the truth is I don't know beans about what sort of power doorbell circuits
carry.

I know they run at a low voltage.  That's clear from the wiring used.  And
I can see the step-down transformer.

I also know that the solenoids in the doorbell itself have to be powered
by a DC current.  Applying AC to a solenoid accomplishes nothing.

But I don't know whether the current is rectified at the transformer or
inside the doorbell.  If the former, I might be able to connect it
straight to the 7805 voltage regulator inside the box.  If the latter, I
need a rectifier circuit.

So - can anyone tell me exactly what sort of current I can expect to find
in a doorbell circuit?  And what I would need to condition it before
feeding it to a 7805 voltage regulator?