----------
> From: Peter (Chee Foon Tiang) <tiangcfoon@HITACHI.COM.MY>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Piezo speaker with PIC -> formula for musical notes
frequencycalculation
> Date: Sunday, May 31, 1998 10:15 PM
>
> Somebody mentioned on the PICLIST:
>
>    http://www.dontronics.com/see.html#sound
>
> However, I don't think they produces the correct pitch on the
> musical scale.
>
> So you might like to try my formula for musical tone
> generation....
>
> Theory of Operation
> ===================
>
> i.   The note "A" below "middle-C" is defined as 220 Hz.
>
> ii.  An octave higher/lower corresponds to frequency
>      doubling/halving, i.e.,
>
>      "DO", "RE", "MI", "FA", "SO", "LA", "TI", "DO"
>       ^                                         ^
>       |                                         |
>       +-----------------------------------------+
>               one octave / 2x frequency
>
> iii. You have 12 semitones (including flats and sharps) in an
>      octave.
>
> iv.  The pitch(freq) increases exponentially going up the scale.
>
> Formula
> =======
> Therefore,
>              ___
>      k = 12 /           (twelth root of 2)
>           \/  2
>
> where k = multiplier to the next semitone.
>
> if you natural log the above formula, it would be clearer,
>
>     ln k = ln 2 / 12
>
> Calculation
> ===========
> So, you have,
>                                    ___
>              "DO" / middle-C = 12 /    * 220 * 3
>                                 \/  2
>                              = 261.63 Hz
>              "DO" is 3 semitones above the reference note A.
>
>     and,
>                                    ___
>              "RE" / D        = 12 /    * 220 * 5
>                                 \/  2
>                              = 277.18 Hz
>              "RE" is 5 semitones above the reference note A.
>
>     etc.
>
> So use a spreadsheet to calculate the frequency for the notes
> in the octave that you want to cover and the corresponding periods
> and reload values for your timers.
>
> I'm sorry that I do not have the PIC codes (haven't done one).
>
> I do have the assembly codes for Hitachi's 4-bit, C codes for
> 8-bit and 16-bit uC.
>
> And by the way, although the PIC I/O ports can drive relatively
> high current, it would be safer to use the circuit below (which
> I think is relatively simple and cheap).
>
> Regards,
>
>
> Peter Tiang
> Design & Applications Lab
> Hitachi Semiconductor(M) Sdn Bhd
>
> ====================================================================
>
> >>> Mark Devin Newland <ape@eskimo.com> 30/May/1998 11:49am >>>
> I just build up my proto board for a similar project but used a 2N7000
> instead.  However, I do not have the tone formulas and graciously ask
> for a copy.  Thanks in advance
>
> Peter (Chee Foon Tiang) wrote:
>
> > Drive the buzzer thru a pnp transistor as thus:
> >
> >                               +5V
> > I/O    10k          100k      |
> >  ---/\/\/\/\---+---/\/\/\/\---+
> >                |        E_____|
> >                |     B |/
> >                +-------|\__
> >                         C  |
> >                            |
> >                            /
> >                           /
> >                          +-----+
> >                          |     | BUZ
> >                          +-----+
> >                             |
> >                            GND
> >
> > Use a "frequency-controlled" type of
> > buzzer (which works like conventional
> > speakers), and you can generate
> > various frequency to your liking.
> >
> > If you like I can mail you the formula
> > for generating melodies, like
> > "DO, RE, MI", etc.
> >
> > Regards,
> > Peter Tiang
> > ======================================
> >
> > >>> NCS Products <ncs@WORLDNET.ATT.NET> 29/May/1998 09:04am >>>
> > I want to add sounds to a product--beeps and boops and the like.
> >
> > Can I just hook a piezo speaker to a PIC output pin?
> > Or should I use a resistor and/or capacitor in series?

Peter:
Would it be better for the trnsistor to put the transducer in the emitter
circuit?