mattell starmaker guitar, with optical pickup system...

[bluebunny]

You get a "Like" from me, Jimi, just for the camera spin at the end.   

[duck_arse]

here see my current log, for testing.



more pics can be seen here:

https://imgur.com/a/9UKYqDp

as can be seen, my string height makes for difficult fretting. I have a small bit of wood with the screwdriver as fret, and I think this is how I will proceed. you need to tension the string w/ finger above the fret to hold it in place, give a whang, and it sounds like a koto, possibly from the wooly sounding speaker hopping around the bench, possibly the screwdriver wobble. but then it will start to feedback, so you just do bends in the extra space the fretboard isn't.

and it sounds like a theremin, wooooo-ooo-ooOOOO-------oooo. like that. dual twin optical pickups, select switches, one goes to the inverting and one to the non-inverting pins of the 386, and you just dial in how mad you want it. I think I will tidy-up the single sliding fret when I get to the finished version, and let the customer do his own slip-in fretboard for proper notes.

still no proper string fitted. will draw up the circuit soonest, it's dead easy, no reason not to build one.

[amptramp]

For a single-string instrument, there is always the possibility of using a lever at the end of the string that tightens or loosens the string, sort of like a whammy bar but with enough authority to give you several octaves.  Give it a scissor grip and you will have a fine instrument.  No need for frets.

[pinkjimiphoton]

gah! its a damn diddly bow, play it with a slide or a beer bottle ffs!

[anotherjim]

I found a slot interrupter in my stash and had a mess around with it. The receiver side is a photo BJT and what I did is drive the LED+CLR from an opamp with a pot feeding a variable Vref to the +input. The BJT is wired as an emitter follower and fed back to the opamp -input. Probably over complicated but it lets me try a few bias settings and see if there's any linear range to be had. Test output is from the opamp. Anything interrupting the IR forces the output to switch.

All I've done so far is try a few "string sizes". I can confirm that anything too thin won't work at all. The IR just bends around and carries on regardless. The string has to be capable of totally blocking the IR. Looking at a datasheet shows these things have a DIN standard. There are several "aperture" size choices and this could relate to how thin your string can be. Most hobby supplies only stock one kind if any so you'll get whatever minimum string size that kind has.

[pinkjimiphoton]

interesting, and thanks for the confirmation. the manual says .054 string. so i imagine that or bigger, actually, the string i got on there may be undersized and may be why it has issues tracking right.








pics for fun

[duck_arse]

I changed my 60lb leader for an ernie ball 36, whatever that means. works fine with the dual mouse sensor/s. and I've found how to tune the pickups. and - the single fret on a block means you can slide the fret right up towards the pickups, and then hammer/bang on the string fret and nut, if you want to get clanky feedbacks and overtones.

[anotherjim]

I do intend to make a plank instrument, but I want to try a more direct way of achieving the sustainer that doesn't make so much noise as the speaker would. To that end, I've got a bunch of freebie PCB relays to scavenge electromagnets from to make a vibrator type input to the string.

I suspect it won't hurt much to put short sleeving over a smaller gauge string. It only needs to fit within the opto and maybe won't mute or futz the harmonics.

Is weedwhacker (strimmer) wire a good string for this? Comes in different gauges. I know it gets used for tea-chest bass.

[amptramp]

I do intend to make a plank instrument, but I want to try a more direct way of achieving the sustainer that doesn't make so much noise as the speaker would. To that end, I've got a bunch of freebie PCB relays to scavenge electromagnets from to make a vibrator type input to the string.

I suspect it won't hurt much to put short sleeving over a smaller gauge string. It only needs to fit within the opto and maybe won't mute or futz the harmonics.

Is weedwhacker (strimmer) wire a good string for this? Comes in different gauges. I know it gets used for tea-chest bass.

If you are using electromagnets, doesn't the wire have to be magnetic?  You could use plastic wire and add a ferrite bead over the area near the solenoid and shrink sleeve where the pickup goes but I doubt it has the strength for what you want to do.

[anotherjim]

No, I'm planning on a vibrator on the string somewhere somehow - not an E-bow type magnetic operation.

[amptramp]

The vibrating wire oscillator here on pages 52 - 53 would be a good place to start:

https://worldradiohistory.com/Archive-Radio-Electronics/60s/1968/Radio-Electronics-1968-05.pdf

This articles shows vibrating wire filters and oscillators.  The oscillator is interesting - it has no capacitors.

[anotherjim]

I'm thinking at the moment of having a vibrating bridge but still driven by feedback like the Starmaker.

The vibrating wire thing I know as a Reed system. Reed as in the reed of a saxophone - better called a Tine in this case? They were once used in FDM data transmission systems. Old tech, but still used on some UK railways for train detection where the transmissions are in the rails and different non-harmonic feed frequencies discriminate which section of the line the train is at. There's actually a pair of mechanically coupled reeds and one is driven by a coil and if the frequency is right, the second reed vibrates in sympathy and induces a current in an output coil. The detector has to be well isolated to avoid external vibration.

[duck_arse]

here see in full colour, my single pickup, double-detector version. I haven't tested the phase switch as drawn with R9, but it does work by wire swapping and hard-grounding. the bass boost option seems to actually cut highs, which will greatly reduce the horrible hiss you get at higher drive levels.

align the pickups over the string by measuring the drain voltage of either fet, while switching between the two detectors, while they are lit.

[anotherjim]

Found this image of pickup response...

Interesting, although OT that the Piezo is one direction like the Opto. I suppose force sensing, like light, is a more or less thing, it doesn't have polarity. I guess the signals in the diagram are of a muted pluck.
From an incomplete and seemingly abandoned article here...
https://www.acs.psu.edu/drussell/guitars/pickups.html

Eagerly awaiting Stephens demo.

[duck_arse]

I would argue the optical respones, I looked at waves with both sides (now). will do screenshot tomoz.

[pinkjimiphoton]

another one turned up. sold literally instantly. bummer!

https://www.ebay.com/itm/334303690236?mkpid=0&emsid=e11021.m43.l3160&mkcid=7&ch=osgood&euid=c34cdd7711544b5fa5f55ad98d919e83&bu=43184490039&ut=RU&osub=-1%7E1&crd=20220125050019&segname=11021&sojTags=ch%3Dch%2Cbu%3Dbu%2Cut%3Dut%2Cosub%3Dosub%2Ccrd%3Dcrd%2Csegname%3Dsegname%2Cchnl%3Dmkcid&nma=true&si=wUC4oG2qDpbhsOl0CeYIwlU15rM%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557

[Ben N]

here see my current log, for testing.

Les would be proud.

[anotherjim]

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.

[amptramp]

Philco made a "beam of light" record player cartridge back in 1941 - 1942 where there was a light bulb and a photocell transforming needle position into voltage.  In the article below, a guy uses back-to-back photodiodes to replace the photocell and this may be a good idea to minimize frequency doubling or quadrupling:

http://billthompson.us/bt/philco-beam-of-light-restoration/

[matmosphere]

Very cool, and that demo is hilarious. "Here 1980's parent, give your child a small pointy box that makes sounds like doom." So great!!

I haven't had a chance to read the whole thread, just the first couple of post, but I'm wondering if one could 3d print some kind of case for a multi-string LDR-LED setup. Need to read through and see how exactly it is working though.

here see my current log, for testing.

Les would be proud.

Agreed!

To me a string on a stick with a crude bridge and a screwdriver, that looks interesting!