mattell starmaker guitar, with optical pickup system...

[duck_arse]

crude? how very dare you, sir!

use the ball-mouse sensor and led, mount on an end-bit of the cover flap from a video cassette, and allow that sliding screwdriver to bounce up and down as it will, you get much more fun and games.

here see top pic is the neck-sensor front element top trace and the bridge front bottom trace.



and here the neck rear top and bridge rear bottom.




200mV div / 2mS div - voltage at the fet drain,using a different fet for front and rear element.

pardon the crappy pics - I don't have a cable release, makes it a bit difficult to twang and shoot.

will this pass for a demo, Jim?

also. I've gone binary post count.

[duck_arse]

I will add: I love the idea of the hotwheels fret, sounds like the kind of thing. also, bashing about on the benchtop, and just cause, I'm trying to think of a way to add a whammy bar, to increase or decrease the mechanical contact of the speaker, so feedback can be wooo-ed in and out.

I tested the phase switch [shown in my circuit previous page] tonight and it does work on the breadboard. the string I'm using is a D, but I'll ship with an A, user can suit himself. I have a proper tuner on the way.

[pinkjimiphoton]

Modern optical pickups go very close to the bridge. Presumably to reduce string movement when you fret/bend strings since the set of the string in the sensor is critical. The Mattell pickup looks to be about in a position similar to a normal bridge pickup - well it had to be to avoid the speaker chassis. So, for consistent operation, the action needs to be low, the fretboard with a minimal (if any) relief bend in it (but plastic so could be warped!) and a pretty taut string. D_A's travelling fret avoids this somewhat.
Incidentally I think the traveller should be a Hotwheels track and car chassis - 'cause Mattell! 

I already started my log build. Aiming for a 25" scale. It's got a proper tuner I had in spares box and will actually use a metal "A" string since that seems easiest. About 1mm dia seems optimal for my sensor. That 25" is the shortest scale guitar I have (an SG) so if it's justified I can copy fret positions from that.
I drilled for a wire tunnel under the pickup in the SG bridge position before I realized it might be better right after the bridge but I'll go with what I have to begin with.
Since I have a metal string, my sustainer probably will be magnetic action.

there's a 1/8th" thick metal bar that runs inside, almost the whole length of the guitar.
i'd go with an e string, it needs some mass. i haven't had a chance to find the proper tuning range, but it's a combo of
string guage and tension that makes it come to like.
be curious to see if it will drive well from a scale length this long!
also curious if its worth it to try and devise a 6 string variant just for shits n giggles.

[anotherjim]

will this pass for a demo, Jim?

It will, but not everybody can hear waveforms. 

Jimi, thanks for confirming the "toy" has a truss. But, does the string bend down much at the pickup when you play the top fret?

[pinkjimiphoton]

barely matters to it. the action is kinda high. i'll get measurements next time i'm in the dungeon

[anotherjim]

Well, the action matters on my log.
I just got the Opto fitted and wired to a breadboard.
Set good, it sounds like you'd expect a guitar to sound. Very low noise, plenty of output. But bend the string down to fret it on higher notes and it splutters out.  Works reliably close to the nut of course. No adjustment can let it play high up notes. I do have a high action at the moment but I wanted to see how sensitive it was. I will move the pickup close to the bridge and recess the log so the Opto can go lower and the action can come down. Anyway, close to the bridge would be wise if there are frets and you do bends - and the gap thru the Opto is fixed so the string can't move far off centre.
Can play it with a slide all the way, ping harmonics etc. Sweet!

[pinkjimiphoton]

nice. i gotta gig, i was supposed to be workin in the dungeon, but i popped in on petey twofinger's youtube and got sucked into his latest release. holy shit.

formant sitar is my new favorite thing on the planet.

anyways, pitch of the string is important... gonna take some messing with the string needs a fairly high tension to sing, and the action on mine is about where most of the basses i've played seem to end up.
when you find a tuning where it starts to feedback the open string, and then can find an effectively useful range from that tuning... it will have dead spots somewhere, but you can minimize by "shifting" them beyond where the fingerboard ends, if that makes any sense. there's a sweet spot where most of it will ring.

also note, if you wiggle the string BEHIND the bridge, it seems to affect the attack and feedback sustain on more troublesome notes.

its a weird toy. i wanna build one into like, a teisco or something, polyphonic

can someone 3d print some opto's into some bridge pieces? lol

[matmosphere]

can someone 3d print some opto's into some bridge pieces? lol

Maybe, I'd certainly try if you want. Could you draw a pic or diagram of what you think might work?

[duck_arse]

Well, the action matters on my log.
I just got the Opto fitted and wired to a breadboard.
Set good, it sounds like you'd expect a guitar to sound. Very low noise, plenty of output. But bend the string down to fret it on higher notes and it splutters out.  Works reliably close to the nut of course. No adjustment can let it play high up notes. I do have a high action at the moment but I wanted to see how sensitive it was. I will move the pickup close to the bridge and recess the log so the Opto can go lower and the action can come down. Anyway, close to the bridge would be wise if there are frets and you do bends - and the gap thru the Opto is fixed so the string can't move far off centre.
Can play it with a slide all the way, ping harmonics etc. Sweet!

can you show a photo of yer sensor, Jim? how wide is its aperture?

[anotherjim]

One of these...
https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=302_303&products_id=2948

The one I have is to this standard but is old & I don't know the brand. A BJT symbol for the logo and made in Mexico.

[pinkjimiphoton]

can someone 3d print some opto's into some bridge pieces? lol

Maybe, I'd certainly try if you want. Could you draw a pic or diagram of what you think might work?

way above my paygrade, bro, but thought it may be cool to make optical bridge pieces if it were possible somehow

[matmosphere]

I made 3d printed bridge saddles for my electric twelve string and they are holding up fine. I was just having a tough time visualizing the needed form factor.

[matmosphere]

So, what type of bridge? How close to the point where the string and the saddle meet do you want the ldr's, what about height?

Rough ideas are fine, the mad-scientist in me is far more mad than scientist.

[pinkjimiphoton]

us mad scientists need to stick together so fuzzy goodness never disappears from this land!


i was just thinking it would be cool to make the actual bridge saddles, like on, say, a strat be self contained with the opto stuff. but it seems crazy, cuz you'd still need to have the string pass thru the gap, so i dunno how to make THAT work out lol

[anotherjim]

See the Wilcox optical system. The sensors are in the saddles, but I think they are reflection type sensors. The string does not sit inside but over the top.

[pinkjimiphoton]

ok, here's some extra crappy video with measurements n stuff for string action at nut, bridge, etc etc.
i can't really get at where the sensor is to accurately measure it, but one of the components has a white stripe on it, facing kinda toward the nut... and the string is over the other side from that. its weird. its enclosed on like 3 sides from two angles.

anyways... extra crispy stoner version stupid diddly bow trick

[anotherjim]

FWIW, here my sensor circuit for now...

I found its best with the trimmer set for 4.5v with no string in the gap, then adjust the height for about 2.25v for a centred string.
Note the phototransistor is wired as a buffer and with the overall negative feedback to the opamp, the signal output is the opamp action as it tries to track the vibrating string.
Now, it's probably too clean for Jimi as I suspect from the sound it makes, the Mattel isn't linear for the fuzzy/buzzy tone.

[duck_arse]

AJ - pretend I'm stupid and don't know what optical axis means. what does optical axis mean? which direction, what happens?

[amptramp]

AJ - pretend I'm stupid and don't know what optical axis means. what does optical axis mean? which direction, what happens?

The optical axis of the light is not the entire area within the device, it is the position where the light from the LED goes to the photodetector.  The light is collimated (parallel) so there is no effect from diffuse light.  The optical axis is the height where the string would go to center it in the light beam.  It is at the height of the LED and phototransistor.  The direction of light travel is from LED to photodetector but for most purposes (including ours), the direction does not matter.  If the device is mounted flat on the guitar, it is sensitive to the height of string motion, not the side-to-side transverse movement.

[anotherjim]

The photo interrupter does as its name suggests. The output switches when something breaks the Ir light beam across the slot. Some have moulded lines to show the actual axis, mine has nothing apart from one side that has the part ID printed on it. They are usually used in non-fussy on-off situations where a flag on a linear moving thing (e.g. print head carriage) or holes in a rotating thing do or don't interrupt the slot.

With the Opto now 15mm in from the bridge, my log is much happier.
I've also hooked up a 6v relay coil simply driven by a 2N7000 off the phototransistor emitter. Just loose for now, so holding it E-bow style does the job but I'll need frets for it to work properly as the rough wood damps the string too much when fretted. No problem with a bottleneck though.

Incidentally, I don't have the need for a sweet spot string tension like the Mattel does. I suspect the string pressure on the bridge affects how well the speaker vibration gets it resonating for feedback. I can downtune the log to stupid doom bass.