Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!purdue!haven!adm!cmcl2!phri!cooper!gene
From: gene@cooper.cooper.EDU (Gene (the Spook) )
Newsgroups: sci.electronics
Subject: Re: Sine wave generator
Message-ID: <1595@cooper.cooper.EDU>
Date: 20 Jul 89 22:20:15 GMT
References: <790@serene.UUCP>
Organization: The Cooper Union (NY, NY)
Lines: 23

in article <790@serene.UUCP>, gbell@pnet12.cts.com (Greg Bell) says:
> 
> 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???

1) You might try the piezo element, complete with "ding-dong" driver IC,
that Radio Shark used to, and possibly still does, sell.  Loudness is ok
in a reasonably quiet room, but don't expect to hear it above your
vacuum cleaner or power tools.

2) Those light bulbs act as variable resistances in a feedback network.
To oscillate properly, the loop gain must be exactly unity. If it's less,
the signal won't regenerate and it will die out; if it's more, the output
will saturate and your sine wave will become badly distorted (chopped off
at the extremes).

You might want to try a ~wave-generator-in-a-chip like an XR2208 (Exar)
or an 8048 (Intersil).  Loads of fun.

						Spookfully yours,
						Gene