On Tue, 07 Nov 2006 03:24:14 GMT, Art Todesco
wrote:

[snip]

I didn't know they made SPDT doorbell buttons. Every one I've seen has
been SPST. SPST would be enough for controlling relays too.

There is a whole line of switches made
for these things. Actually, they are
not strictly SPDT, but are momentary
SPDT with a center off (the rest
position).

I've seen the ones that work like 2 SPST switches with a common
button, where you press on one end to close one switch, the other end
to close the other switch. They may be designed with a common
connection. Such a switch might be used with a 2-coil latching relay,
for on and off. I don't know why you'd use one for a doorbell.

BTW, I have been considering such a switching circuit for my bedroom.

[snip]
--
48 days until the winter solstice celebration

Mark Lloyd
http://notstupid.laughingsquid.com

"God was invented by man for a reason, that
reason is no longer applicable."