[geeks] Doorbells

[James Fogg]

> >One of projects on my list is to make a network enabled, MP3 playing
> >doorbell.  Although, I was thinking to make mine wired.
>
> I used to have a computer-connected doorbell.
>
> It sent me a text message of "RING" if I was logged in, or email
> if I wasn't.
>
> It was a simple switch wired to a serial port on a 3B2.


Since I have a PBX in the house, I use a doorphone. It's a little box
with a speaker and one pushbutton. Press the button and selected phones
around the house ring. Answer the phone and you can talk to the person
outside (duplex, no one-way stuff).

Otherwise, a doorbell (traditional) is a 1 amp 12 volt AC transformer, a
series switch and an electro-mechanical bell. Couldn't be simpler. You
can build a solenoid that strikes a tube (copper pipe would be my
choice). 1 amp @ 12V can drive a lot of plunger. Design the solenoid so
the long-stroke momentum will drive the plunger out farther (and hit the
bell) than its normal energized resting position (so the plunger
retracts after hitting and doesn't muffle the ring). A loosely wound
spring is usually the solution.