> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
> Of slippyr4
> Sent: 07 October 2006 21:06
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] audio frequency sine oscillator help needed
>
>
> >
> > Why not use a little logic and think about it yourself?  Even
> better, build
> > it and look at the output.
>
> I certainly will build it on monday. The logic behind it is a bit
> beyond my understanding of electronics - i'm only a hobbyist with no
> training in electronics.
what you have to understand is that a square wave can be thought of as an
infinite number of sinewaves added together with each sinewave having a
greater frequency (the first one is at the frequency of your sqare wave then
3 times it then 5 time it then 7 times it and so on) but smaller amplitude
(i don't remember the exact figures but they can be obtained through the
fourier series) than the previous. BTW what is your level of maths
education? you will find analog circuit theory very hard to understand
properly without at least a moderate understanding of calculus.

olins circuit works roughly as follows

the first two resistors hold the line at mid rail when your output is hi-z,
this way as long as you make your output hi-z when not producing tone you
shouldn't get any clicks (clicks are typically the result of filtered
versions of a sudden change in the average voltage).

the next 3 RC pairs act as filters passing the low frequency components of
the infinite series of sinewaves but rejecting the higher frequency
components.

the final RC pair (note the opposite pairing and very much higher RC
multiple) blocks the 2.5V DC offset from the output.


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