Hi Dale,

I want to clear up some things for you. In music mathematics the interval
between D and E is a full tone. between D and D# and D# and E is a half
tone. Each half tone is divided into 9 intervals called "comas" (I'm not
very sure about how the intervals are called in English because English is
not my mothers tongue, so sorry about that :)).
The scale is like this C-C#-D-D#-E-F-F#-G-G#-A-A#-B-C. Between E and F and B
and C there is only a half tone as you can notice. I play guitar and I have
a lot of friends at the local Music Academy who taught me this things. An
experienced player can distinguish between the coma intervals. All the
tuners I saw where displaying the note (C,D,..B) and with 9 LEDS the drift
from the center note (one center LED and 4LED's for above and 4LED's for
under domains).I never saw one with 19LED's for each comma one though.
In my opinion you have to split a half tone at least in two other intervals
to get a acceptable tuning.
If the tuning is bad to say a half tone error, yours kid ear will "learn"
to hear the false note and that will be a great disadvantage for him in the
future. It's very hard to unlearn something like this it's like a reflex and
it's very hard to get rid of them. If you can't make it right please buy a
tuner for your child's sake and don't be offended by my advice because it
has
happened to me and I speak from my own experience. It took me two years of
studying to unlearn an to learn the good notes and still have sometimes
trouble with that when I'm tired.
As for the circuit I would first amplify the signal a bit and adjust the Z,
then apply the LPF, then convert the sine wave to square wave outside the
PIC
for a better control and to spare the PIC from spikes. You will never now
what musicians are able to plug into your device ;).

Hopping that helped you a bit,
C'ya

Mircea Chiriciuc
EMCO INVEST

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