mattell starmaker guitar, with optical pickup system...

[pinkjimiphoton]

i looked into one of them a while back, from all i could glean on the interwebs, it amounted to run, don't walk, away... lol

[anotherjim]

Luthier work is on hold due to weather. All I wanted to do was round the back of the neck portion for comfort and get that out of the way to save constant stripdown/rebuilds with the fittings My workshop is also my studio so I have to do a lot of dusty/painty jobs outdoors.
But I have now got some kind of flat & hard fingerboard fitted to the log to get clearer fretless fretting.
In the meantime, I got a couple of TCRT5000 sensors to play with.
Datasheet...
https://www.vishay.com/docs/83760/tcrt5000.pdf
A basic test shows it can see small wires longways, that is the string passes over the centre line across both the LED and Phototransistor. I think because the light path is normally broken it's easier to detect anything that enters the path and reflect some infrared back. Only 5.8mm wide so a breeze to fit them side by side on a guitar.

Is there a shorter way to write "infrared phototransistor"?

[pinkjimiphoton]

irpd? lol

[anotherjim]

I've seen IED for the infrared LEDs, logical but it's probably not something you'd want the security services to hear you saying.

[anotherjim]

This is an interesting device if you don't mind squarewave outputs...
https://www.application-datasheet.com/pdf/honeywell/hlc2701-001.pdf
It's a dual Ir detector with Schmitt trigger outputs for an optical mouse but also fuzz or midi guitar I reckon. Use with a common IRED (a better acronym). Has a 3rd eye sensor in it to compensate for drift.

[anotherjim]

MkII stick now has frets (and a zero-fret, no nut), an adjustable brass bridge and the original interrupter Opto - easier to mount for one & height adjustable in normal pickup fashion. Oh and a basic plywood box on the side to house the electrics.
I put a plain G string on it this time. Remember it didn't look like this Opto can see thin strings so I expected I'd have to put a bit of sleeving over the string where it passes thru the Opto gap. Blow me, it works anyway as it is! Have sound and is pretty clear too. I'm not sure about the physics of this - it even seems to have a wider working area in the Opto gap.

Development still won't be fast, I want...
Onboard 3.7v rechargeable LiPo battery power. A battery check LED for this.
DC-DC boost converter for 12v. Regulated 9v for a stable Opto setup.
Single-ended LM386 sustainer drive from +12v. I think it will suit the 6v coils I have + I found some stronger ones with slightly lower DCR. A way to move the magnet away from the coil pole so it doesn't drag the strings natural sustain.
Drone oscillators for a Hurdy Gurdy thing.
Fuzz/distortion for the Opto guitar output for ordinary guitar sustain.
A ton of cosmetic work so it doesn't look like the recycled junk it actually is.

I got the battery and boost working on the breadboard with the Opto circuit and it seems ok. No whines and it isn't even screened yet.

[pinkjimiphoton]

MkII stick now has frets (and a zero-fret, no nut), an adjustable brass bridge and the original interrupter Opto - easier to mount for one & height adjustable in normal pickup fashion. Oh and a basic plywood box on the side to house the electrics.
I put a plain G string on it this time. Remember it didn't look like this Opto can see thin strings so I expected I'd have to put a bit of sleeving over the string where it passes thru the Opto gap. Blow me, it works anyway as it is! Have sound and is pretty clear too. I'm not sure about the physics of this - it even seems to have a wider working area in the Opto gap.

Development still won't be fast, I want...
Onboard 3.7v rechargeable LiPo battery power. A battery check LED for this.
DC-DC boost converter for 12v. Regulated 9v for a stable Opto setup.
Single-ended LM386 sustainer drive from +12v. I think it will suit the 6v coils I have + I found some stronger ones with slightly lower DCR. A way to move the magnet away from the coil pole so it doesn't drag the strings natural sustain.
Drone oscillators for a Hurdy Gurdy thing.
Fuzz/distortion for the Opto guitar output for ordinary guitar sustain.
A ton of cosmetic work so it doesn't look like the recycled junk it actually is.

I got the battery and boost working on the breadboard with the Opto circuit and it seems ok. No whines and it isn't even screened yet.

WE NEED PICTURES!!!! 

[anotherjim]

Since I've been asked nicely and although it meant finding some glass plates and flash powder, here are some exposures...



The last one is a selection of bits including some electromagnets from relays. The one in the middle was my original choice from a 6v SPDT relay with a less prepared example at the far left. The larger one with the cable is what I hope to use now and it's from a 6v DPDT relay. Also a LiPo cell and a DC-DC boost converter module.
I've started to make fit the control bits.
I put the tuner at the heel end, there's just a peg on the headstock for the string ball end. The steel angle device between the tuner peg and bridge has a sideways guide slot for the string to make sure it passes the centreline of the saddle and winds on low enough to keep the string tension down on the saddle.

Important! It's only available in left-handed configuration! 

[pinkjimiphoton]

that thing makes me.... happy.

[anotherjim]

The Guity Gurdy is alive. No demo recordings yet.
It got an onboard USB charger for the battery.
I found the sustainer works without a permanent magnet. The coil is under a cupronickel plate. The opto sensor got an alu' cover to keep the sun out.
Fret markers exist as white dots along the upper edge of the fingerboard.
The green blob is the battery test button.
I like to think that the rectangular box is an accidental nod to Bo Diddly -  because, Diddly Bow!

[bluebunny]

Neat, Jim.  You deserve extra "Likes" for the Bo Diddly/Diddly Bow quip alone. 

[duck_arse]

it looks a bit different to the others I've seen.

[iainpunk]

The Guity Gurdy is alive. No demo recordings yet.
It got an onboard USB charger for the battery.
I found the sustainer works without a permanent magnet. The coil is under a cupronickel plate. The opto sensor got an alu' cover to keep the sun out.
Fret markers exist as white dots along the upper edge of the fingerboard.
The green blob is the battery test button.
I like to think that the rectangular box is an accidental nod to Bo Diddly -  because, Diddly Bow!

woah man, brings back memories from 10+ years ago
my first DIY instrument was a diddly bow, using a drawer from a broken cupboard as the box, and a plank as the neck. an improvised tuner from a hinge, wingnut and bolt, and no tuning stability at all. i was inspired by Shane Speal and Justin Johnson, but people always told me that i copied ''sea sick steve'' which annoyed me. i still play the hubcap gitter as my main instrument.

cheers

[deadastronaut]

come on jim, do a demo ...dying to hear this thing.

[anotherjim]

I'm trying Rob, but every time I pick it up, I get mesmerized by the drones and forget to record it.

[deadastronaut]

Thats a good sign then...,cool. 

[anotherjim]

Guity Gurdy is now soundclouded...
https://soundcloud.com/ashdalestudio/guitygurdyhitsthebong
...Get those bongs lit!

[deadastronaut]

that sounds great....love it.  nice work man. 

[pinkjimiphoton]

Guity Gurdy is now soundclouded...
https://soundcloud.com/ashdalestudio/guitygurdyhitsthebong
...Get those bongs lit!

you sick freak

lol

[anotherjim]

Purely for the record since I doubt anyone is mad enough to repeat it, here is a schematic...

Starting top left is the LiPo battery system. The charger is built in - it's a commercial one on a little board taken out of its box and pushed in some heatshrink. I took the green OK led off it and wired it to a 3mm one by a micro USB socket. The USB socket was fun - nobody makes chassis/panel mount USB so I got a little breadboard friendly break out module board and mounted it on two 3mm x 10mm hex standoffs and fitted it to a bit of alu' angle with a hole cut for the charger plug to enter. Standard 5v USB micro charger required.
The battery check is crude but useful. Normally it gives a Red power-on indication. Press the button and it switches to green if the battery is in tip-top condition. If it gets to a lower in-between state, the red and green can be lit meaning it's okay but re-charging advisable. Solid red means its close to unusable. By that time, using the sustainer will cause Reg1 to drop and the drones will go out of tune.

The DC-DC converter is a module with a little multiturn trimmer and the only defence I put in to reduce RF emissions from it was twisted pair wires in and out and filter capacitors then mount it in a little ABS box with a slugtape screening wrap. These modules have only a few caps on input and output. They should probably be used with ferrite LC filtering at both ends.

I used 78L08 for Reg1 as I happened to have them, to save a little power and I didn't know how high the voltage for the sustainer needed to be until I finished it.

The Opto sensor Tx was given a simplified adjustable drive with the opamp basically being an adjustable voltage reg. The Rx was equally simple so I only had to route 3 wires thru the body. The preamp stage doesn't need an explanation, but I put the feedback diodes in sockets so I could experiment with them - more for output level purposes than tone. It then goes to a standard opamp mixer but also splits off to...

The 386 amp for the sustainer coil. Of note is the polarity/off control. The flyback protection diodes were only added as I was going to fit a sliding on/off magnet on the coil so it might induce high voltage but I ended up not using a magnet at all.

Then there are the drones. One LFO gets inverted and both low-pass filtered to drive the BJT modulators. Basically a rip from Escobedo's PWM effect snippet. Increasing the LFO speed causes the filters to attenuate the LFO to the point it has no effect, so the LFO needs no depth control (short of space!). The drone oscillators get PWM in opposing phase so it doesn't cause level drop when pulse width gets narrow. I added the switch so the drones can be muted individually with only one switch. Player can use this to toggle between drone pitches. The drones get high & low pass filtered to edge the pulse waves closer to sawtooth.
Next, they hit the output mixer after a volume control.

Th, th, that's pretty much all folks!