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Optical Pedals


Mr Alex
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My dad repairs welding machines, and one common problem they have is the pots breaking in tig controller pedals, it appears that construction welders aren't easy on their gear, it usually isn't the pot scratching it the gear being ripped off of it from too much pressure. Being a nuisance job, it isn't worth them what they charge to change them. So armed with a new weeping demon I'm gonna be making some pedals based on the optical system in it, because the welding industry hasn't caught on yet. My prototypes will be a dual volume/tone pedal set up, cos the volume pedal is essentially what is needed, but with a different pot and a few other resistors. And I want a volume pedal.

I plan on making a retrofit unit eventually for them to fit be fitting.

I'll be hopefully making the first prototypes this week from some 3mm ply, and later if they are good, I'll do them from aluminium.

If anybody has any experience with optical pedals, I'd be glad to hear about what works and what doesn't.

If it works well I'll make a tutorial, cos optical pedals are way better IMO than pot based pedals, and I'll be designing a superior wah(if things go well) soon. I say superior in the meaning that It'll be the best parts of the crybaby(old skool ones), with the technology of the weeping demon, and my own mods added in for good luck.

And thanks in advance if anybody can help me out.

ooh, and if anybody has a whammy schematic(I'm not joking either) I'd like to see it

thanks

Mr Alex

Edited by Mr Alex
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My dad repairs welding machines, and one common problem they have is the pots breaking in tig controller pedals, it appears that construction welders aren't easy on their gear, it usually isn't the pot scratching it the gear being ripped off of it from too much pressure. Being a nuisance job, it isn't worth them what they charge to change them. So armed with a new weeping demon I'm gonna be making some pedals based on the optical system in it, because the welding industry hasn't caught on yet. My prototypes will be a dual volume/tone pedal set up, cos the volume pedal is essentially what is needed, but with a different pot and a few other resistors. And I want a volume pedal.

I plan on making a retrofit unit eventually for them to fit be fitting.

I'll be hopefully making the first prototypes this week from some 3mm ply, and later if they are good, I'll do them from aluminium.

If anybody has any experience with optical pedals, I'd be glad to hear about what works and what doesn't.

If it works well I'll make a tutorial, cos optical pedals are way better IMO than pot based pedals, and I'll be designing a superior wah(if things go well) soon. I say superior in the meaning that It'll be the best parts of the crybaby(old skool ones), with the technology of the weeping demon, and my own mods added in for good luck.

And thanks in advance if anybody can help me out.

ooh, and if anybody has a whammy schematic(I'm not joking either) I'd like to see it

thanks

Mr Alex

Check out Morley Wah Pedals.

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I know about morley they created the optical pedals as I understand, but they just aren't that good in my opinion(compared to a weeping demon, and they cost more)

have you ever seen inside a WD, there are 9 pcb's, it's scary stuff.

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I also repair welding equipment and an optical pedal wouldn't last two hours in that environment. We do use an optical rotary encoder on the automated and panel-mount controls but the footpedals survive longer with mil-spec sealed pots. Inductive pots like we use on joystick controls last forever but they are very noisy electrically and require 12 vdc to work. Only available in 10k or less. Johnson uses opticals on their footpedals but you have to wipe your feet before you use them and clean the little film-arm twice a year. Never tried or seen a Morley.

Tell your dad to visit our repair forum: welddoctor.net. Lots of welding and fab. stuff aimed at the repairperson.

Edited by thedoctor
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I'm not sure why it wouldn't work, you mentioned it wouldn't stand up to the welding environment, his boss was VERY impressed by the weeping demon, and the led/fence/ldr setup it uses instead of a pot. Maybe you are referring to photocouplers, we spent a lot of time researching them and they would be to expensive and would waste our time, I want good quality effects, he doesn't want to replace pots, AND he wants happy customers.

and I doubt your site has ANYTHING that they wouldn't know already, one thing my dad does is designs controllers for spot welders so their work is a little more than straight repairs.

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Check out Paul Morressy's Scratch Built Wha from where this quote from me comes...

As an alternative...you might want to see if you could adapt the thing to a hall effect control. Morley use optics to adjust their wha's but I've a Boss Volume pedal that uses a hall effect sensor and a magnet and the action is really good...no friction and no scratchy pots...plus, easier than making those gears if you can find a circuit to do it...

Otherwise...nice build...BTW: I love working with aluminium :D

pete

Check out hall effect devices...a hall effect (3 legged) chip reacts to the presence of a magnetic field...the pedal has a magnet on it...as it moves towards the chip it can operate like a solid state pot...works great on my volume pedal...As it's not light dependant it could be completely covered...you'd need to in a welding environment as bits of metal would try and attach themselves to the internal magnet...anyway, the circuitry is way small for this (2cm sq tops)...

just a thought...

psw

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PSW, I had seen that before, but took no interest at the time, it is interesting though. I will certainly stick with the led/ldr as it is simple and cheap to build(as long as I keep the pedal to the same range, and make the fence the same as the Ibanez one.).The reason I posted this is one, I was hoping somebody had done this before, and could tell me if they had any problems and what to do about fixing them(I'm by NO means and electrical guru, and I think my dad is probably sick of me pestering him for help with my effects pedals)and two, I was hoping somebody had a whammy schematic(even if it requires cmos chips.) or just a schematic for an adjustable pitch pedal for 2 octaves up and also one down.

edit: my zoom pedal had a hall effect sensor.

Edited by Mr Alex
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A Whammy, a harmonizer or any other useful pitch shifter, is either going to be a DSP implementation, an analog delay-based approximation of a digital algorithm, or a complex analog multiplier like the Bode/Moog frequency shifter. Each one has its own set of problems, but the one thing they all have in common is that they aren't very DIY-friendly.

There's an analog "harmonizer" on Mark Hammer's site ( http://hammer.ampage.org/ - go to page 5), but it's definitely not a beginner project, and Ray Marston's 4046 Circuits (same site, bottom of page 7) will show you how to generate harmonic multiples of an input signal frequency using a CD4046 PLL and a divide-by N counter chip, but that'll only give you fixed intervals, so it's not really much use either. There are a few DSP-DIY projects in development on the 'Net, but nothing that really qualifies as ready to build. There hasn't been much serious interest in reverse engineering the Whammy, but you're certainly welcome to try your hand at it - it's probably cheaper to just buy one. :D

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Actually MrAlex, I was hoping he would find time to contribute to the welder repair forum, as noone on the forum knows everything. Maybe, as you said, he has his hands full taking care of your immediate needs. My bad.

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lovecraft: I know it isn't beginner friendly, but I have access to the entire farnell and rs catalogs, and some specialist ic makers, so I can get parts, I might forget it for now though. thanks for your help though.

thedoctor: he is pretty busy at the moment(and sees the internet as a alternative to the fax, and little else,so he wouldn't bother with your forum), also they are agents for some spotwelder companies, and the market here is really starting to boom now, as car companies are specifying spot welding only for repairs now, more people need good gear. And as I'm not at school anymore, I have too much time on my hands so I'm always hasseling him for help with stuff.

psw: that was a possibility at one point, but only for my uses in audio. for the welder pedals, the tracks are being ripped up(even on the wire wounds) or the pot shafts are snapped off long before it would be making any noise. so removing the pot is the only way to go, and it needs to really be low maintenance. I will have to remember that circuit for when my friend gets his new crybaby(fool).

any nobody needs to post anything else, you've all helped, but obviously nobody has tried making optical pedals before. once I've got something going, I'll make a tutorial with measurements and everything.

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Lord, forgive me! I must be the Michael Jordan of forum posters! I shall try to adjust my input to those of you who know basketball!

Optical pedal control is not only old tech but is is in revision because of it's shortcomings. I should have and shall in the future leave the improvements to the "pros".

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Lord, forgive me! I must be the Michael Jordan of forum posters! I shall try to adjust my input to those of you who know basketball!

Optical pedal control is not only old tech but is is in revision because of it's shortcomings. I should have and shall in the future leave the improvements to the "pros".

Probably just me, but I dont understand a single thing you just said. Don't worry though, I'll figure it out once I've got some sleep.

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...and I doubt your site has ANYTHING that they wouldn't know already...

...nobody needs to post anything else, you've all helped, but obviously nobody has tried making optical pedals before...
Notice anything about these quotes? It's just my personal observation, but if you ask for help, it's less than gracious to complain about the quality of said free help, and really bad form to imply that those trying to help aren't bright enough to do you any good. You sound like a bright kid - you might want to work on those social skills a bit so people will listen long enough to find that out.
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...and I doubt your site has ANYTHING that they wouldn't know already...

...nobody needs to post anything else, you've all helped, but obviously nobody has tried making optical pedals before...
Notice anything about these quotes? It's just my personal observation, but if you ask for help, it's less than gracious to complain about the quality of said free help, and really bad form to imply that those trying to help aren't bright enough to do you any good. You sound like a bright kid - you might want to work on those social skills a bit so people will listen long enough to find that out.

sorry to come across that way, I haven't slept much recently(mother VERY sick) and I'm beginning to get grouchy.

that first quote, I'm serious, they are the spot welding experts for New Zealand, and there isn't much they can't do, usually just case repairs that I do for them when I'm around.one dude through his welder when it was faulty!!!!

and the second one, you have all definetly helped, I'm not denying that, but from what I can tell, nobody has actually made something like I'm trying to do, they have offered alternatives, which I will keep in mind, as I may find that making the fence is too diffucult, and I may find future uses for them too. so thankyou.

I didn't mean to come across as complaining either. and if I implied that others weren't bright enough to do any good, woah, sorry, I'll just have too be less grouchy and re-read things more often.

sorry for any offense I have caused

and please dont call me a kid, and I'm hardly bright, I dropped out with 4 hours school work left to finish 6th form. I'm just incredibly practical,e.g. my first guitar body(practise) I cut with a hatchet, as my tools were in storage. If I cant get something, I make it. simple as that.

Edited by Mr Alex
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...and please dont call me a kid...
Sorry, no offense was intended there - at my age, pretty much everybody under 35 or so qualifies as a kid. OK, here's some things you need to consider when designing an optical pedal:
  • Spectral response of the resistive element -you need to know what kind of light your LDR responds to best, and optimize your light source for driving it. LEDs are more reliable and long-lasting than any other cheap low current light source, so they're probably the way to go there, but there might be compelling reasons to use something else
  • Attack and decay times and resistive response curve for the LDR - most CdS photocells are fast attack/slow decay, and they're all over the landscape so far as exactly how fast/slow they are. You might try using a phototransistor or photoMOSfet, they're faster, but they're going to limit the headroom and may distort the signal if pushed very hard.
  • Fence design - the fence can be anything from a rigid mask with a cutout to litho film carefully printed with varied widths of parallel lines and spaces to vary the amount of transparency, but it's going to have to be colorfast enough not to fade and robust enough to survive repeated cycles of movement without cracking, bending or tearing, or moving away from the LDR's aperature (if it wears out faster than a carbon pot, it's kinda pointless to go to the trouble). It's also going to be challenging to get the "taper" of your virtual potentiometer right - paralleling it with a fixed resistor will help, but it's still going to take a fairly precision fence design (and implementation) to get the result to act anything like a standard pot.
  • Mechanics - you're basically designing a film projector that uses the same short piece of film over and over again. It can be as simple or as complex as you choose, but it has to be fairly consistent over the pedal's range of travel. Morley manages it, so I know it can be done.

I've thought about this idea a lot over the years, and I never have been able to make the cost/benefit analysis work for me, but I really don't see huge advantages in the optical pedal to begin with, so you may (justifiably) feel differently. Craig Anderton's Volume Pedal Descratcher pretty much eliminated the only problems I had with potentiometer-based pedals, so I haven't given it much consideration since. If you think it's worth the effort, go for it - you might teach us all something! :D

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You can call me kid LK...I'm ever so slightly younger I believe.... :D

Anyway...I just wanted to say that I look upon PG as a database of ideas not just a question and answer service...

Though I was aware that it wouldn't necesarily suit your intentions (welding) that this thread will be looked at now and by those searching through (as people encouraged to do) and such related information is of benifit to those considering, in this case, effects building...

Although you may even have had your questions answered some further discusion around the topic often brings out interesting discussions, links and related ideas that may be helpful to others and go on longer than the originator ever intended....

Who knows in 6 months time we may be pointing someone directly to this thread for advice...perhaps not even related to welding... :D

pete

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lovecraft, thats the best info I've probably been given in my life! seriously.

some of those things I've already thought about, I'm gonna remove the fence from my weeping demon and copy it so if I give the pedal the same range then within reason I should get a good taper going. My dads got some lensed leds in stock, so I'll have to experiment with those, and I understand ldrs to be far from linear, Is that correct?

thats ok bout the kid thing too.

psw, this is for more than just welding, my prototypes will be active volume and tone pedals so I can keep my lap steels without controls(cept pickup switches, and maybe some masters for preamps).

as I dont own any other wahs at the moment, I'm not sure if this is limited to weeping demon's, but I use mine as a feedback sustainer mostly, once I've found the sweet spot I get screaming infinite sustain.

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, but I use mine as a feedback sustainer mostly, once I've found the sweet spot I get screaming infinite sustain.

Oh NO!!!!!!!!!...you mean all my sustainer experiments are obsolete...all I needed was a Wha...

Maybe I just don't have a "sweet spot".... :D

pete

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, but I use mine as a feedback sustainer mostly, once I've found the sweet spot I get screaming infinite sustain.

Oh NO!!!!!!!!!...you mean all my sustainer experiments are obsolete...all I needed was a Wha...

Maybe I just don't have a "sweet spot".... :D

pete

no they're not obselete, people(read *alex*) want globs of sustain without the overdriven scream sometimes. Im gonna put a sustainer in my current project with some piezo coax in the bridge.

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My dads got some lensed leds in stock, so I'll have to experiment with those, and I understand ldrs to be far from linear, Is that correct?
Yeah, not very linear, but you don't want a linear taper for a volume anyway, so it's a "feature" you can exploit. I think that Cadmium sulfide cells are most responsive in the yellow range (580-620nm? that's from memory, so don't hold me to it.), but I do know that a few people have had good results using a red LED for homebrew Vactrols. Using the right combo of photocell, fence shape and parallel resistance, you should be able to get just about any response curve you like, but it's going to be a long, laborious process. That's where being like Ibanez, with a lab and a serious R & D budget really comes in handy! I'd go with a large dark resistance LDR (like >10 Megohm), and adjust with a parallel trimmer pot, using the fence density to set your taper. Let us know how it works out for you. Could be quite interesting!
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I have a turntable from the early 70's that has a piece of film with a pattern etched into it that swings with the needle arm - it breaks off a bit of the audio signal, runs it to a LIGHT BULB, and puts it through the film. When a phototransistor on the other side of where the film swings reads down to a certain voltage, it stops the motor.

It's pretty funny, but I doubt it'll be in any way helpful.

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