> > Hi Christopher, how many different frequencies
> > do you need, and how accurate does each one have
> > to be? 20Hz t 400Hz is not a very big range.
> > -Roman
> >
>
> Preferably all 380, but in the program I cut it down to 20Hz  to 255Hz.
with
> one value for each frequency. This was so that all the registers were kept
as
> 8bit . Also about 5% accuracy is alright.....I worked out a table
> for each of the values.....just implementing it into the program is a
> problem.. :)  I hope that helps.

Saying "all" 380 makes no sense here, since there are an infinite number of
frequencies between 20Hz and 400Hz  I guess you mean all the frequencies
that happen to come out to integer values when measured in Herz?  OK, but
that contradicts your 5% accuracy requirement.  400Hz/20Hz is a frequency
range of 20:1.  At 5% accuracy, this can therefore be covered by Log1.05(20)
= 62 different frequencies.  You need to decide what your requirements
really are.

A simple way to produce different tones is using the PWM output as a square
wave generator.  However, the lowest frequency generated that way is
oscillator/16,384.  You could use either a slow clock if the PIC has little
else to do, or an external divider after the PWM output.

Another way is to use timer 1 with a CCP module in compare mode.  This gets
you a 16 bit period register.

Another way is to do it all in software.  This is feasible in your case
because your frequencies are so low.  Even a 12C508A can do this, but I
don't know what other features you need to decide which frequency to emit.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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