pic microcontroller discussion list <> wrote:
> I need to generate a 1300Hz ish sine wave pulse, from a pic, that I
> can plug into a tape recorder's line in jack to log.
>
> Obviously, it's fairly easy to get a 1300 Hz square wave, but what
> can I do to simply and easily smooth this out a bit, so it's
> reasonably close to a sine wave?

Your spec isn't very precise(!), but the first option I would suggest is
driving the signal from two pins, so you get a '3-state' square wave,
sometimes called 'modified sine' by enthusiastic sellers of AC inverters...
It's much closer to a sine than a pulse train is (you can test it by doing
an FFT (e.g. in MS Excel) and comparing the size of the harmonics.

Even better, use PWM and generate a sine from a lookup table.

With either solution, add some form of filter (RC or active, depending on
the smoothness required) to the output.

Nigel
--
Nigel Orr, Design Engineer                 nigel@axoninstruments.co.uk
Axon Instruments Ltd., Wardes Road,Inverurie,Aberdeenshire,UK,AB51 3TT
               Tel:+44 1467 622332 Fax:+44 1467 625235
                   http://www.axoninstruments.co.uk

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