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<DIV><SPAN class=397275015-17112003><FONT face=Arial color=#0000ff size=2>Hey
Robotboy,</FONT></SPAN></DIV>
<DIV><SPAN class=397275015-17112003><FONT face=Arial color=#0000ff
size=2> I am answering this because I have some experience building a
similar thing. Mine is actually working now. Still have some work to do on
the signal processing, but otherwise it is making a
noise.</FONT></SPAN></DIV>
<DIV><SPAN class=397275015-17112003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=397275015-17112003><FONT face=Arial color=#0000ff
size=2>I used a laminated KOHO hockey stick for mine. It is very rigid in
one direction and great for a simple neck. My unit has two strings. It's
also good for fending off drunken audience members.</FONT></SPAN></DIV>
<DIV><SPAN class=397275015-17112003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=397275015-17112003><FONT face=Arial color=#0000ff size=2>I
sawed a flat guitar bridge in thirds and it works great . I used
guitar tuning machines at the head end. A piece of brass rod for the nut
embedded in the neck.</FONT></SPAN></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2>S<SPAN
class=397275015-17112003>ince I am a bassist I have used bass strings, but they
are too fat for this type of thing, so I went to nylon coated beading wire for
now, ( nine strand stainless steel cable ) which is really strong and
great on the fingers. DiAddario ( hope that is spelled right ) string
company is very close to my house so I was thinking of going over there and
asking them for a really long guitar string. : ) You don't have to use metallic
strings with photo pickups either, so you can try Weedwacker string which is fat
and light.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>Well as far as the photo pickups go you have to be sure
that you collimate the output of the LEDs. Meaning the light should not spread
too much or the bulk of the intensity modulation will take place outside the
diameter of the phototransistor. So you can mount the LED in a tube of some sort
to prevent the beam from spreading too much. I am using flat top LEDs from Radio
Shack. I re-polished the tops so that they were extra flat and they work really
well when placed in a tube. In addition to that you have to offset the
phototransistor slightly from the LED. I am using two phototransistors per LED.
One for the bottom half of the string ( mounted below the string ) and
one for the upper half ( mounted below the string ). This way I get the
variations that occur on the top half and the bottom half of the string
movement. I need to figure out the phase requirements yet, because I know that
there has to be an inversion in there somewhere to get a relevant signal. The
sound is pretty buzzy at this point, but it is working.
</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>LED
U</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>String
| </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>Phototransistors
HH </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>The pickup must be placed at the peak of one of the
string nodes otherwise you may end up with little or no signal.
When a string vibrates it divides itself up into nodal sections which are equal
to half of the string length ( also other mathematical relationships to string
length, but they are much smaller and insignificant in this case). So on a
guitar there are three points where the string movement is minimum. The nut, the
twelfth fret and the bridge. Therefore your pickup should be placed at a point
one quarter the distance from end to end for max amplitude. The commercial
versions of this type of thing have these pickups integrated into the bridge.
Mine did not work well that way so I moved it. They may be using a reflected
laser or something which would make sense in that case. Mine is picking up the
string interrupting the LEDs beam directly.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>I am working on feeding a portion of the signal back
into the stick to create a drone. This was suggested by another list member . He
suggested using a thingamajig that basically vibrates your car like a subwoofer
without actually being a speaker. I forgot the name exactly. For me that is too
big, so I am trying to figure out what I want to use at this point. It may end
up being a dual coil which effects the string directly (that was also
suggested), sort of like an Ebow. Or if I go to Weedwacker string then I will
use a motor type device ( Like a
solenoid ).</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>Hope this rambling helps you
out.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003>Michael <BR></DIV></SPAN></FONT></FONT></FONT>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=397275015-17112003></SPAN></FONT></FONT></FONT> </DIV>
<BLOCKQUOTE>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B>
owner-synth-diy@dropmix.xs4all.nl
[mailto:owner-synth-diy@dropmix.xs4all.nl]<B>On Behalf Of
</B>Robotboy8@aol.com<BR><B>Sent:</B> Sunday, November 16, 2003 10:30
PM<BR><B>To:</B> synth-diy@dropmix.xs4all.nl<BR><B>Subject:</B> [sdiy]
Photoelectric String<BR><BR></DIV></FONT><FONT face=arial,helvetica><FONT
lang=0 face=Arial size=2 FAMILY="SANSSERIF">I posted about this a long while
back, before Ireally got my ideas together, but now I'm asking again and with
someslightly different questions, as the design has changed a LOT.<BR>I'm
thinking of building a single-string... thing... for very lowtones. Something
of a cross between an additive synthesizer, electricbass, and string bass.
Allow me to explain further before you beginpelting rocks at me: it'll be a
single string (any reccomendations onwhat to use? bass guitar strings? garage
door cable? picture-hangingwire twisted around itself?) running the length of
a piece of wood (4or 5 feet). Towards the bottom it'll have a set of three
infrared LED'sabove and in line with the string. These can be turned on and
offindependently. Beneath the string (and directly beneath the LED's) willbe a
total of 3 photoresistors and 3 phototransistors (2 components perLED). These
are varying a current being passed through them separatelyand then mixed
together before running to the output. The 'volume' ofeach can be changed by
knob. Phototransistors will output square waveswhile photoresistors will put
out slightly more sine-ish waves, andnone of them will be quite in phase with
one another, so it shouldn'tbe just a mushy square output.<BR>Okay, so now for
the questions.<BR>1. Am i crazy/stupid for even wasting anyone's time asking
this?<BR>2. Any suggestions on what string type/length to use? (it'll be
tuned/tunable but fretless).<BR>3. Any general construction tips?<BR>4. Any
clue what the decay time will be like?<BR>5. Anything I've forgotten?</FONT>
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