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'[EE]: Guitar input'
2002\06\09@130451 by Dale Botkin

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On Sun, 9 Jun 2002, Russell McMahon wrote:

> I could provide component values for say 2 and 4 poles of low pass if you
> are interested.

I am interested.  I did some searching & reading and came up with this:

----/\/\/\/\------|-----
    3.3K         |
                 = .47uF
                 |
                GND

If I read the stuff I found on passive LPF design right, that should give
me a 102Hz cutoff, correct?  But I'm not sure what effect the bias
resistor(s) for the transistor will have.  I will gladly take advice and
suggestions on this matter.

I changed the tag to [EE] because we've drifted pretty much completely
away from the PIC aspect, but here's a quick overview of the PIC side.

The PIC (I'm using a 12CE674 for development, but will switch to 12C671
for real) looks for a low pulse on its input, which *should* be the peak
of the cycle of the string's fundamental frequency.  We start Timer 0
running and wait for the next pulse, indicating the next cycle.  If Timer
0 overflows, we increment a high-byte counter, ending up with a 16 bit
counter for the cycle time.  We accumulate 32 of these samples, then
divide by 32 for an average (crude, yes, I know - I may work on that).

Now comes the interesting part - since we know the desired freq of each
string, we look to see if it's more than halfway between the lowest (E)
and the next highest (A).  If so, look to see if we're more than halfway
between that and the next highest (D).  We keep doing that until we figure
out which string has been plucked, and use two LEDs to indicate whether
we're below or above that string's desired frequency.  There's a little
hysterisis so you can be within some range - right now I have it set up
for 6.25% (1/16 of the cycle time) for testing.  I don't know how close
"close enough" is when tuning a guitar, so we'll play with that once we
have it working; it's a simple software change.

The automagic string selection is neat, but also means means you could
tune, for example, the D string to a G (assuming you don't snap the bloody
thing in the process), so you have to be more or less in the ballpark to
begin with.

It's really a pretty neat little gadget, we're planning to connect it to
the amp input and mount the LEDs on the amp control panel.  The amp we're
building will use a National LM3875 driving an 8" full-range speaker.
We're roping Grandpa in to do the woodworking for the cabinet.  Figure if
he gets serious about it (who knows, the kid's 13) we can always build him
a tough little tube amp.

Dale

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2002\06\09@151341 by Olin Lathrop

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> ----/\/\/\/\------|-----
>      3.3K         |
>                   = .47uF
>                   |
>                  GND
>
> If I read the stuff I found on passive LPF design right, that should give
> me a 102Hz cutoff, correct?

Yup, 102.6 Hz, +-20% for the component <g>.

> The PIC (I'm using a 12CE674 for development, but will switch to 12C671
> for real) looks for a low pulse on its input, which *should* be the peak
> of the cycle of the string's fundamental frequency.  We start Timer 0
> running and wait for the next pulse, indicating the next cycle.  If Timer
> 0 overflows, we increment a high-byte counter, ending up with a 16 bit
> counter for the cycle time.  We accumulate 32 of these samples, then
> divide by 32 for an average (crude, yes, I know - I may work on that).

I'm not sure I follow exactly what you are saying, but you can certainly use
timer 0 with pulse interrupts to measure the period.  Using a CCP module in
capture mode will make your life a lot simpler and will improve accuracy
because you don't have to worry about being in a timer 0 overflow interrupt
when a pulse comes in.  I've done a bunch of frequency/period measuring
projects, and CCP modules are real handy for that.


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2002\06\09@175812 by lintech

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On 9 Jun 2002, at 12:02, Dale Botkin wrote:

>  The amp we're
> building will use a National LM3875 driving an 8" full-range speaker.

Don't know the chip but my 30w valve amp drives  18" for bass
guitar - not sure you will be happy with 8"...


George Smith

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2002\06\09@193116 by Jinx

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> The automagic string selection is neat, but also means
> you could tune, for example, the D string to a G (assuming
> you don't snap the bloody thing in the process), so you
> have to be more or less in the ballpark to begin with

When stuck for tuning, I could always use 50Hz hum as
a G. The difference between semitones is the twelth root
of 2 = 2 ^ - (1/12) = 2 ^ 0.083333 = 1.059463. Multiplying
E1, 41.20Hz, goes F1 = 43.65, F1# = 46.24, G1 = 49.00
which is near enough if that's the only reference available.
I don't recall the band ever being paid a visit by the Concert
Police A440 Squad

60Hz users have a choice between A1# (58.27) and B1
(61.73) - 60Hz is smack in the middle. As his tuning ear
develops he'll find it easier to judge. One thing you really
want to avoid is having the strings tuned too high for long
periods - it does the neck or machine-heads no favours

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2002\06\09@235138 by Dale Botkin

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On Sun, 9 Jun 2002, Geo wrote:

> On 9 Jun 2002, at 12:02, Dale Botkin wrote:
>
> >  The amp we're
> > building will use a National LM3875 driving an 8" full-range speaker.
>
> Don't know the chip but my 30w valve amp drives  18" for bass
> guitar - not sure you will be happy with 8"...

As the parent of a budding young 13 year old bass player wannabe, I can
assure you of two things:

1.)  The amp will be throttled to a fraction of its rated power, and
2.)  An 8" speaker will be quite sufficient for a while, trust me.

8-)

Dale

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2002\06\10@002101 by Jinx

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> 1.)  The amp will be throttled to a fraction of its rated power, and
> 2.)  An 8" speaker will be quite sufficient for a while, trust me.

Suggestions - a headphone outlet, and a built-in metronome

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2002\06\10@002109 by Dale Botkin

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On Sun, 9 Jun 2002, Olin Lathrop wrote:

> > ----/\/\/\/\------|-----
> >      3.3K         |
> >                   = .47uF
> >                   |
> >                  GND
> >
> > If I read the stuff I found on passive LPF design right, that should give
> > me a 102Hz cutoff, correct?
>
> Yup, 102.6 Hz, +-20% for the component <g>.

Well, seems to work OK.  Wow, crash course in audio LPF design.  I could
even do it with an op amp now (and still may).

{Quote hidden}

Sorry, I did meander about the point a bit.  I'm using Timer0 because I
just want to use the 12C part, and it's a pretty simple task.  I'm 99%
sure it's all OK aside from the analog input stuff.

By the way, I just tried the above circuit, fed by a 1uF cap and connected
to the existing 330K/56K bias resistors.  Almost there, the amplitude is a
tad low but it looks a lot cleaner.  The PIC did lock onto the E string a
few times, and saw A and D a couple of times.  At this point I'm thinking
it might be a lot easier to connect to the amp output instead of the
guitar input.  Anyawy, looks like we're almost there.  Now I just have to
figure out how close to perfect pitch is close enough for a bass.

Dale

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2002\06\10@013519 by Jinx

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> Now I just have to figure out how close to perfect pitch is
> close enough for a bass

Hope you're not thinking of fobbing your boy off with
2nd best ? Unless he's going into free-form jazz, play
with an extremely loud drummer or go native and get
into Watusi chant "anyting tuning you got be fine by us,
we just jump about de place over here" accompaniments

==========================================

Bit of a side-track here, but I think it's interesting. It doesn't
affect boy-bands btw

There is some debate about absolute tuning, particularly
the relationship between instruments. Not all scales are
equal. For example, frequencies that are true to the scale
of a piano tuned to C, are not the same as a piano tuned
to the scale of D. This is because calculated intervals do
not transfer between scales. Say you were playing an
orchestral piece mostly in A major. Everything sounds
wonderful as all the instruments were tuned to intervals
calculated from A440. Then the piece changes to C major.
To the cogniscenti, jarring dischords can be heard as
instruments clash as they move away from their base tuning.
It's what they'd claim to be the difference between a good
piece and a great piece of music

I was once asked to make a tune-shifting keyboard - if it
detected a key change, then all of the notes would change
tune based on the key now being being played. The man
who asked me to do it unfortunately died, but I have a
feeling that work is going on, if not completed to do this

http://www.izzy.net/~jc/PSTInfo/Temper.html

"An interesting thing happens if you actually play a cycle of fifths
using only intervals which are perfect natural fifths, that is where
each interval is exactly (3/2)fo. If you start with fo = A0 = 27.5 Hz,
then the twelfth interval will result in f = 3568.02 Hz. If on the other
hand, you start at A0, and play perfect octaves up to A7, you will
get f = 3520 Hz. This can be quickly verified on a hand calculator;
try it. This difference in pitch between the twelfth note of a natural
fifth series, and a natural octave series of 48.02 Hz results in a
pitch error of 24 cents, almost a quarter of a semi tone. If on the
other hand, you play a cycle of fifths using intervals which are each
slightly flat by just the right amount, when you reach the twelfth interval,
you will end with f =3520 Hz! If each fifth in the series is flattened by
the same amount and the adjustment distributed evenly throughout
the cycle, it works out that each fifth should be played flat by 2 cents.
When the resulting twelve notes are all shifted, by octaves, into
ascending order, the result is an equal tempered chromatic scale.
The spacing between the notes of this scale will have intervals
which are all equal"

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2002\06\10@034548 by Mircea Chiriciuc

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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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2002\06\10@041458 by Russell McMahon

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> Bit of a side-track here, but I think it's interesting. It doesn't
> affect boy-bands btw
>
> There is some debate about absolute tuning, particularly
> the relationship between instruments. Not all scales are
> equal. For example, frequencies that are true to the scale
> of a piano tuned to C, are not the same as a piano tuned
> to the scale of D. This is because calculated intervals do
> not transfer between scales.

etc

Sounds like OT to me but I'll play.

Have you ever tried to use a Fife for accompaniment.
Would be an Interesting exercise in frustration.
The song doesn't go " ... with your Musket, Fife & Drum, ..." for no reason.

Irving Berlin, who wrote more songs than Jinx has good ideas, including the
allegedly all tiome favourite "I'm dreaming of a White Christmas" (a song,
not one of Junx's ideas) could only play the piano in F sharp (all black
notes ?) and had a piano with a knee opetated lever to adjust the key to his
requirement while he played it in the single key. probably couldn't play the
Fife either.

       RM

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2002\06\10@050336 by Russell McMahon

face
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> Bit of a side-track here, but I think it's interesting. It doesn't
> affect boy-bands btw
>
> There is some debate about absolute tuning, particularly
> the relationship between instruments. Not all scales are
> equal. For example, frequencies that are true to the scale
> of a piano tuned to C, are not the same as a piano tuned
> to the scale of D. This is because calculated intervals do
> not transfer between scales.

etc

Sounds like OT to me but I'll play.

Have you ever tried to use a Fife for accompaniment.
Would be an Interesting exercise in frustration.
The song doesn't go " ... with your Musket, Fife & Drum, ..." for no reason.
For all who thought PICs were the most arcane creation ever and/or to learn
all about rolling in, rolling out and cork adjustment and why fifing
flautists tend to do it backwards and fall flat see -

       http://www.beafifer.com/twentythree.htm

or worse still the home page at         http://www.beafifer.com/index.html
:-)

Irving Berlin, who wrote more songs than Jinx has good ideas, including the
allegedly all time favourite "I'm dreaming of a White Christmas" (a song,
not an idea) could only play the piano in F sharp (all black notes ?) and
had a piano with a knee operated lever to adjust the key to his requirement
while he played it in the single key. Probably couldn't play the Fife
either.

Jinx has done it again. I REALLY should be working !!!!


       RM

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2002\06\10@055408 by Jinx

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> Jinx has done it again. I REALLY should be working !!!!

A smart fish wouldn't have fallen for the bait ;-)

I found the discrepancies bewteen scales interesting after
being taught the "conventional" and simplistic do-ray-me.
Thought it worth mentioning to Dale merely as background
(noise or info - take your pick)

It's like that day at tech when we were told that pH wasn't
what we'd been taught for so many years

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2002\06\10@085504 by Dale Botkin

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Hey, I *like* that idea!  Thanks.

Dale
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curiosity killed the cat, I say only the cat died nobly."
         - Arnold Edinborough


On Mon, 10 Jun 2002, Jinx wrote:

> > 1.)  The amp will be throttled to a fraction of its rated power, and
> > 2.)  An 8" speaker will be quite sufficient for a while, trust me.
>
> Suggestions - a headphone outlet, and a built-in metronome

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2002\06\10@100537 by Dale Botkin

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On Mon, 10 Jun 2002, Jinx wrote:

> > Now I just have to figure out how close to perfect pitch is
> > close enough for a bass
>
> Hope you're not thinking of fobbing your boy off with
> 2nd best ?

No, not at all.  I just don't know whether the tuning indicator should
call it good at the base frequency plus or minus nothing, 1Hz, 5% or what.
Just need to figure that out.  I can make it as picky as needed, but
don't want it uselessly picky.

Dale

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2002\06\10@101147 by Dale Botkin

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On Mon, 10 Jun 2002, Mircea Chiriciuc wrote:

> 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"

So if I'm understanding you correctly, it sounds to me like a 5% range
would be close enough, correct?  That would be 1/20 interval, or slightly
less than a coma (1 full tone = 2 half tomes = 18 comas).

Dale

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2002\06\10@131711 by Peter L. Peres

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>> ----/\/\/\/\------|-----
>>      3.3K         |
>>                   = .47uF
>>                   |
>>                  GND
>>

By the way you want the LPF's corner point at or below the lowest cord
fundamental (~40Hz). Otherwise it will do nothing to remove that cord's
second and third harmonics, which is what you're needing it for.

Peter

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2002\06\10@171800 by Olin Lathrop

face picon face
> So if I'm understanding you correctly, it sounds to me like a 5% range
> would be close enough, correct?  That would be 1/20 interval, or slightly
> less than a coma (1 full tone = 2 half tomes = 18 comas).

"In tune" is MUCH closer than 5%.  One note is off from the next by 2 **
1/12, which is only 6%.  You want to be within a small fraction of that 6%.


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2002\06\10@173308 by Jinx

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> > Hope you're not thinking of fobbing your boy off with
> > 2nd best ?
>
> No, not at all.

Just joshing - I know you'd do everything you could

> I  just don't know whether the tuning indicator should
> call it good at the base frequency plus or minus nothing,
> 1Hz, 5% or what. Just need to figure that out.  I can make
> it as picky as needed, but don't want it uselessly picky

Haha, that's very good - "uselessly picky" - just how I was
when I started

If he's playing with himself (oooer) then it doesn't matter
how spot on the tuning is. I expect he'll go through usual
stages of playing along with CDs, then a couple of mates,
and then perhaps a band. Even those bald tattooed scary
people who make CDs for young uns have their instruments
in tune (no, really !!) and he can adjust the bass' tuning maybe
just a little to play along. Whether he's on the same frets as
them, who knows, as there are plenty of alternatives to EADG
(Hendrix tiuned his bass to all flats for example, which some
nasty people might say explains a lot)

A "lady" I once knew back in the punk days played for a band
called the Scavengers (hmmm, cute). Her rhythm guitar was
tuned for her to an open-string  Gmaj chord by the lead
guitarist. All she had to do was make a straight barre across
the strings to change chords. None of that messy which-
finger-goes-where-for-Eminor nonsense. Please make him
get further than that

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2002\06\10@181104 by Jon Baker

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I can hear anything more than about 1.5% up or down from the correct tone.
The guitar tuner I use is supposed to be accurate to +/- 0.5% .. and that
one was a freebie.  It may not sound that bad when you pluck a single string
(when its slightly out of tune), but when you strum a chord and two strings
are out of tune even slightly - it can sound awful.

I imagine a slightly out of tune bass guitar- with its lower frequencies-
the beating would be just as- if not more noticeable than on my 6 string.

--
Jon Baker
Amateur Guitarist

{Original Message removed}

2002\06\10@192031 by Bob Ammerman

picon face
I believe the poster was referring to a 5% error _between_ semitones. This
is only 5 cents, and thus inaudible, I would expect, to all but the very
best ears.

Bob Ammerman

{Original Message removed}

2002\06\10@200752 by Jinx

face picon face
> I believe the poster was referring to a 5% error
> _between_ semitones. This is only 5 cents, and
> thus inaudible, I would expect, to all but the very
> best ears.

I agree, anyone with perfect pitch would be able
to hear the difference. Almost all people could not
tell the absolute tuning of one instrument on its own

Get two together with slightly different tuning - ugh

You could produce a 440Hz "A" reference tone from
a 20MHz crystal using 4040s and 4081s. Divide the
20,000,000 by B18E ( b'1011000110001110' ) to
get 440.00Hz. Or you could use a 16-bit timer if it's
not busy. Further divide this by 8 to get 55Hz for the
bass A string

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2002\06\11@031911 by Mircea Chiriciuc

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> So if I'm understanding you correctly, it sounds to me like a 5% range
> would be close enough, correct?  That would be 1/20 interval, or slightly
> less than a coma (1 full tone = 2 half tomes = 18 comas).

Sorry, sorry, sorry!
I made a huge mistake! A tone is divided in 8 microtones, so a half tone is
divided in 4 microtones. It's also easyer to compute and the accuracy is
acceptable for a begginer (0.5Hz). If he will need more accuracy in the
future you'll see at that time.
I think the ideea with the build in metronome is very good and practical
too.

How did I came up with 9? Don't ask me. I've been very clumbsy yesterday.
(o:o)

Mircea Chiriciuc
EMCO INVEST

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2002\06\11@040031 by Vasile Surducan

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>
> You could produce a 440Hz "A" reference tone from
> a 20MHz crystal using 4040s and 4081s. Divide the
> 20,000,000 by B18E ( b'1011000110001110' ) to
> get 440.00Hz. Or you could use a 16-bit timer if it's
> not busy. Further divide this by 8 to get 55Hz for the
> bass A string
>
  440.14 Hz using hardware PWM, rectangular waves
 A good musician will heard diferences as low as 0.2Hz pure sinusoidal
signal. Unfortunately I can't... :o)


Vasile

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2002\06\11@081152 by Roman Black

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Hi Dale, maybe a variation on the TV sync-separator
circuit, using one transistor? This will detect only
the very peak of each wave, and is self adjusting.
With the simple low pass RC filter this should give
good triggering on your wave as the harmonics are
much lower in amplitude. I don't think that zero-cross
or any half voltage conversion to digital will work
as well. :o)
-Roman


Dale Botkin wrote:

{Quote hidden}

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2002\06\11@104011 by Dwayne Reid

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At 11:14 PM 6/9/02 -0500, Dale Botkin wrote:
>On Sun, 9 Jun 2002, Olin Lathrop wrote:
>
>Well, seems to work OK.  Wow, crash course in audio LPF design.  I could
>even do it with an op amp now (and still may).

Something to consider is the output impedance of the bass pickup.  I used
to build DI boxes for getting musical instruments into PA system mixing
consoles and one of the things I learned early was just how sensitive to
loading those pickups can be.

You may wind up with a whole lot more level if you buffer your low pass
filter with a simple 1 FET buffer (source follower or simple amplifier) -
input impedance will increase to the value of your gate resistor (1M0 or
so) and gain will be just under unity (follower) or about 5 or so (common
source amplifier).  Almost any N-channel JFET will do - the old standby
2n3819 or any of the J112 family.  Just be sure to operate it from your
unregulated supply - most JFETs (2n3819) need between 7 - 30 Vdc to
operate.  You will also need a coupling capacitor between the FET and input
of your low pass filter to keep the DC out of the PIC input.

One final thing to increase the sensitivity of the PIC's input - consider
biasing the input pin to about the nominal threshold voltage of the
pin.  That is about 1.4 Vdc for a standard pin and 2.5V if it is a schmitt
trigger pin, assuming 5V operation.  Add the bias network right after the
coupling cap but before the LPF so that you don't attenuate the desired signal.

dwayne

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2002\06\19@003830 by rusque (Listas)

face
flavicon
face
Hello Roman,

> Hi Dale, maybe a variation on the TV sync-separator
> circuit, using one transistor? This will detect only
> the very peak of each wave, and is self adjusting.

   do you have (or know where to find) an squematic of this? It seems very
interesting circuit.

> With the simple low pass RC filter this should give
> good triggering on your wave as the harmonics are
> much lower in amplitude. I don't think that zero-cross
> or any half voltage conversion to digital will work
> as well. :o)

   The waveform of an electric or acoustic guitar/bass is very complex. I'm
looking at a bass sample (low E, the thickest string) right now and the 2nd
harmonic (3x fundamental frequency) is about 10dB above the fundamental.
This is a very problem, because if the circuit locks to this frequency the
PIC will think you're playing a B. The funny side of this is that it will
show that the B is in tunning almost exactly when the E is in tune also. :)

   Best regards,

   Brusque

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