Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cwjcc!gatech!hubcap!ncrcae!ncr-sd!serene!pnet12!gbell
From: gbell@pnet12.cts.com (Greg Bell)
Newsgroups: sci.electronics
Subject: Sine wave generator
Message-ID: <790@serene.UUCP>
Date: 19 Jul 89 04:36:06 GMT
Sender: root@serene.UUCP
Organization: People-Net [pnet12], Del Mar, CA
Lines: 29


I recently took on a somewhat dumb "home project".  I wanted to build a
door-bell extension since the downstairs bell isn't audible from upstairs.

The easy way to do this would be to put another doorbell in series (or
parallel?) with the one downstairs.  I tried both ways, but neither worked. 
Either one bell would ring, or neither.  But not both.

So, I thought it would be fun to build a simple circuit that would sense the
drop across the xformer or bell downstairs and generate two sine waves in
sequence, each decreasing in volume (ie. "Ding-dong").

I didn't know what I was in for!  Sine wave generators aren't too trivial.  I
tried one using a 741 with a twin-T circuit in the feedback loop.  This worked
OK, but was hard to tweak into working right.  Also, making the amplitude
decrease turned out to be difficult.

I opened up National's Linear App book and found a zillion different sine wave
circuits.

I'm wondering two things:  What's the best/easiest way of making an electronic
doorbell?  I'd prefer the attention-getting sound of a "ding-dong", that's why
I'm going to all this trouble.  In addition, how do the sine wave generators
that use the PTC of a particular light bulb work???

    Greg Bell_________________________________________________________
      Hardware hacker          |
      Electronics hobbyist     | UUCP:  uunet!serene!pnet12!gbell
      EE major at UC San Diego |