Rough 'n Ready Audio Frequency extraction with a PIC

[HankMcSpank]

I've read a fair bit about this, but I'd like a bit of guidance & a few concepts confirmed or corrected!

I'd like to be able to establish which note is being played on a guitar. I'm only interested from the 'D' string upwards.

The D string frequency is 146.8Hz - which means that one cycle takes 6.81ms. Ok, that's the bit I'm sure about - the rests is fuzzy !

I don't want a lot of complication in the supporting electronics -so ideally I'd like to use the internal oscillator (yes, I know it's rough & ready & not particularly accurate, but I'm not going to be using this to tune the guitar).

I'd thought about using the comparator & basically counting how many cycles have been received in a given time frame - I'd like the time frame to be as low as possible.

Re PICs & floating point - I believe PICs don't do FP - but I'm not sure of the impact to my situation....I'm figuring that the PIC dispenses with the decimal places & just give the integer? (does it round up or just ignore them all together?)

I've created a table to show the lowest possible sampling time frame to be able to get a unique integer for each note, which for this situation works out at about 100ms...

(btw: I didn't know how to format the Excel cells to look ok on here, so I used the code tags - which seems to work ok!)

Note	Freq		Cycles in 100mS
D	146.83		14.683
D#	155.56		15.556
E	164.81		16.481
F	174.61		17.461
F#	185		18.5
G	196		19.6
G#	207.65		20.765
A	220		22
A#	233.08		23.308
B	246.94		24.694
C	261.63		26.163
C#	277.18		27.718
D	293.67		29.367
D#	311.13		31.113
E	329.63		32.963
F	349.23		34.923
F#	369.99		36.999
G	392		39.2
G#	415.3		41.53
A	440		44
A#	466.16		46.616
B	493.88		49.388
C5	523.25		52.325
C#	554.37		55.437
D	587.33		58.733
D#	622.25		62.225
E	659.26		65.926
F	698.46		69.846
F#	739.99		73.999
G	783.99		78.399
E	329.63		32.963
F	349.23		34.923
F#	369.99		36.999
G	392		39.2
G#	415.3		41.53
A	440		44
A#	466.16		46.616
B	493.88		49.388
C5	523.25		52.325
C#	554.37		55.437
D	587.33		58.733
D#	622.25		62.225
E	659.26		65.926
F	698.46		69.846
F#	739.99		73.999
G	783.99		78.399
G#	830.61		83.061
A	880		88
A#	932.33		93.233
B	987.77		98.777
C	1046.5		104.65
C#	1108.74		110.874
D	1174.66		117.466
D#	1244.5		124.45
E	1318.52		131.852

As you can see, by using 100mS, the sample period 'integer' is unique (ie for the number of complete cycles completed).

It should then be a case of a simple Look up Table to work out which note is being played, eg...

If Sample count = 14 then D note is being played.
if Sample count = 22 the 'A' note is being played.

And so on.

So at this embryonic stage...

Is my line of thought correct?

Is there any clever workaround available meaning I could bring that 100mS sampling period down?