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Van de Graaff generator derived triggers - Issues?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Van de Graaff generator derived triggers - Issues?
bwhittington
I'm interested in setting up a patch that uses a Van de Graaff generator as a random trigger but realize I am out of my depth on this and want to make sure to address gear and people safety.

My idea is to place a mic near the discharge wand, send the audio to an envelope follower with gate output and use AND logic to keep the resulting gates in time with a track.

Should the Van de Graaff generator be on its own breaker? Or how can I otherwise isolate its discharges, which I have seen cause interference with other devices on the same circuit before?

At some point with that set up, at least without great care, the charge will surely arc to the mic itself. What affect could that have on the mixer or modules it is connected to? With a rack full of digital modules, a giant electrostatic discharge would seem like a poor idea. I'm ultimately wondering if there is a way to isolate it.

Similarly, is there a safe way to more directly derive a gate from the discharge wand without interfering with its grounding? Mine is connected to generator's ground with banana plugs. I wondered if there might a way to tap into and create a trigger pulse without using a mic. Ultimately the same question pops up here again of how to make sure that voltage doesn't affect other gear. Or people of course.

My generator is a fairly large tabletop version, pictured below.


https://www.sci-supply.com/Van-De-Graaff-p/lc2910-hc.htm
kpreid
I have no personal experience with the matter but I understand that the go-to solution for getting a control signal in/out of an environment like this is optical signals.

That is:
1. Find a fairly sensitive light sensor that you can patch into your envelope follower.
2. Stick one end of a piece of optical fiber up against the sensor.
3. Put the other end of the cable looking right at the VdG arc, or for better results attach it to some kind of gas discharge tube (like a neon lamp or fluorescent tube) that will be in the electrical path of the discharge.

That gets you your trigger signal safely; avoiding electrical interference from being in the vicinity is another story but more amenable to experimentation. I'd tend to expect you're going to get some noise no matter what.
milkshake
A few remarks:

An and gate doesn't insure your random gates are in sync with your music. They are only a bit more in sync than random.

The extremely high voltages will interfere with your other equipment and can easily destroy it. We're talking about thousands of volts.

The pulses from the vd graaf generator are not random.




If you want random gates completely in sync with your music, use an S&H clocked by your master clock or a division of that with noise as input and then put both the clock and S&H output through a logic AND gate.
JohnLRice
Hey Brian,

I'm wondering if you could just use an AM transistor radio to wirelessly pick up the snap of the discharge and then use the raidio's audio out to trigger an Envelope Follower Gate module or similar? hmmm.....
jorg
Hmm, a $5,000 piece of precision electronics and lightning discharge. What could possibly go wrong?

Yikes.

Keep the music gear far, far away from the lightning generator. As kpreid suggests, make an optical connection. For example, point a photosensor at the area where you intend to discharge the arcs. Point it from very far away; use lenses / cardboard tube (i.e. a telescope) to focus it on the action. Maybe quantize the photocell output and gate the quantizer from your sequencer's clock.

And put your whole system in a carefully grounded Faraday cage. And don't sue me when you let all the smoke out of it.
Clockgate
Interesting idea, but as milkshake mentioned, the bursts of high energy electromagnetic radiation from the discharges will probably end up causing clicks in your audio signals.
bwhittington
milkshake wrote:

The extremely high voltages will interfere with your other equipment and can easily destroy it. We're talking about thousands of volts.

The pulses from the vd graaf generator are not random.


I appreciate your comments. And fair enough regarding 'random'. For clairt, what I am after is more 'performed random' combined with dramatic visual spectacle for a live performance, not just randomly generated cv, which would require much less pained efforts to come by, of course. I think a short trigger into an AND should work fine in terms of sync, accepting the the possible variances that might occur.

The nature of the 'interference' itself is what I am hoping to understand here, and what would be required to isolate my gear. Short of that Faraday cage, of course.

JohnLRice wrote:
I'm wondering if you could just use an AM transistor radio to wirelessly pick up the snap of the discharge and then use the raidio's audio out to trigger an Envelope Follower Gate module or similar? hmmm.....


This seems like a brilliant idea, for example. I am certainly familiar with picking up the sound of the discharge on a wireless mic in my education demonstrations of the vdg. At least I assume that is how I am picking it up. I could either try a wireless receiver from my drawer full of broken ones or go radio shopping on eBay to test.

The optical sensor seems similar, except I'm imagining it being a little finicky, requiring the discharge to occur in exactly the same point seems less than idea. And it does still leave the synth wired to a circuit in close proximity to arcing voltages, at least as I am visualizing it. Ultimately it might still ahve the same problem as my wired mic idea.

Clockgate wrote:
Interesting idea, but as milkshake mentioned, the bursts of high energy electromagnetic radiation from the discharges will probably end up causing clicks in your audio signals.


But this kind of gets to the crux of the problem, I think--how is that interference being generated? Electromagnetic radiation sounds like some degree of distance between the two systems might prevent interference? Or is from noise to the electrical circuit? I don't really understand the issue.

What I am wondering now is what steps might prevent/minimize electrical interference--distance, different circuit, power conditioner for the synth, etc? Very happy to listen to another round of why this is a bad idea, too. The why of that would very much be appreciated and helpful though. I can be a little stubborn sometimes but can embrace reason too. wink

Thanks for all of your input.
kpreid
bwhittington wrote:
The optical sensor seems similar, except I'm imagining it being a little finicky, requiring the discharge to occur in exactly the same point seems less than idea. And it does still leave the synth wired to a circuit in close proximity to arcing voltages, at least as I am visualizing it.

These issues are why in my previous post, I mentioned using a fiber optic cable, to get separation with no conductive wires, and a gas discharge tube (neon tube or fluorescent tube), to produce light in a predictable location when the generator strikes it.

Using a junk radio receiver seems like a much better idea, though, because it needs fewer unusual parts and assembly. The best type of receiver for the purpose would be an AM radio since it's more sensitive to, well, amplitude changes, such as are produced by a sudden arc.

Or you might find that all you need is a patch cable not hooked up to an output!
jorg
In my earlier life, I had the task to hunt down glitches/crashes in a product that was going on to a factory floor. That factory floor was a pretty benign environment compared to the VDG. I spent months on grounding and shielding, protection circuits, etc. High voltage arcs will find their way around just about anything. They will travels as waves in the air, snake along cables, and squeeze through cracks in metal enclosures.

If you have an extra synth laying around, by all means play with this. Otherwise, do some research into RFI/EMI, ESD, and related topics.
Clockgate
I would agree totally with jorg. The radiation from discharges like that can permeate into the tiniest of unscreened conductors.

The first radio transmitters were basically spark generators, akin to the VDGG, but with much smaller gaps between the electrodes, and they travelled huge distances.

It's easy to check by running the VDGG, and listening to your audio path. If your equipment is all well screened and grounded, you might be lucky.

Keep us updated, I am interested to see how this progresses.
Yes Powder
I wouldn’t want a Van de Graaff generator in the same room as my modular, let alone electromagnetically coupled to one in any way.There are much better ways to get spectacular pulses, random or otherwise. FUUUCCKKKK!!! FUUUCCKKKK!!!
ranix
I wouldn't put anything that generates 100 kilovolts within 20 feet of my modular. Nor would I attempt to connect the two in any way.
milkshake
bwhittington wrote:


I appreciate your comments. And fair enough regarding 'random'. For clairt, what I am after is more 'performed random' combined with dramatic visual spectacle for a live performance, not just randomly generated cv, which would require much less pained efforts to come by, of course. I think a short trigger into an AND should work fine in terms of sync, accepting the the possible variances that might occur.

The nature of the 'interference' itself is what I am hoping to understand here, and what would be required to isolate my gear. Short of that Faraday cage, of course.



I can't help you with understanding the interference, these high frequencies are tricky and I'm out of my league. But you have an amazing modular synth, please don't destroy it.



Performed random can be done with the patch I described. If you add a DC offset to the noise into the S&H, you can change the percentage of random gates you get. No dc offset will give you 50% chance, adding a DC voltage gives you more than 50%, subtracting less.

Confetti shooters are fun, spectacular and safe.
JohnLRice
Brian,

I just remembered there are devices known as lightning detectors, both commercial and DIY. Below are some links to get you started into further research.

https://www.amazon.com/gp/product/B00EO1H3X8/ref=ox_sc_act_title_1?smi d=A39H7NX79OHQ9T&psc=1



bwhittington
Okay, I've been sufficiently warned off. oops I love the concept, of course, and maybe I will experiment with it sometime with my synth on the other side of the house or something, but particularly when a live show in my world means that there are tables full of other people's gear nearby, this seems like a pretty dodgy idea. I really appreciate everyone's feedback.
Pelsea
Don’t give up, it’s not as dangerous as some folks here think (says the guy with students who build fire organs). To prevent strikes on anything expensive, you can build barriers of thick plexiglas and set the apparatus on a grounded metal table. There are modules built around radio receivers, such as the RF Nomad— they will pick up the discharge just fine.

Thousandsof volts sounds pretty scary, but the current is fairly low.
ranix
thousands of volts will still burn out silicon and the little wires that connect silicon to chip legs, idk I don't like it. It's why we don't shuffle around our sneakers on the carpet when repairing modules
Pelsea
The instructions say people with pacemakers should stay 15’ away. I’d apply that to your synth too. A radio module will pick up the spark just fine, especially if you attach an antenna.

I can see how it would be hard to claim that much room on a stage, though.

(If you want to see something scary, you can watch my blind friend Noel adjust his Jacob’s ladder.)
bwhittington
Pelsea wrote:
Don’t give up, it’s not as dangerous as some folks here think


I tend to agree and can tend to be reckless with my gear partially out of ignorance. And I might feel emboldened by having used one in conjunction with an expensive PA rig for years without incident. But realizing the likelihood of audible pops during a show kind of kills it. You actually probably could extract gates from a running an aux send into an envelope follower. That just wouldn’t be anything the audience would want to hear. Add in the equipment risk, and it seems better suited for bedroom tinkering under more controlled circumstances. Curiosity may have me try the effect for a YouTube vid at some point, but there seem to be are a lot of factors against it in a live setting. waah
Rex Coil 7
Pelsea wrote:
Don’t give up, it’s not as dangerous as some folks here think (says the guy with students who build fire organs). To prevent strikes on anything expensive, you can build barriers of thick plexiglas and set the apparatus on a grounded metal table. There are modules built around radio receivers, such as the RF Nomad— they will pick up the discharge just fine.

Thousandsof volts sounds pretty scary, but the current is fairly low.
Yea but .....
ranix wrote:
thousands of volts will still burn out silicon and the little wires that connect silicon to chip legs, idk I don't like it. It's why we don't shuffle around our sneakers on the carpet when repairing modules
Or why we're supposed to wear grounding wrist straps when we handle a semi conductor or even a PCB with semi conductors on them. Don't bring the damned thing to my studio.
Pelsea wrote:
The instructions say people with pacemakers should stay 15’ away. I’d apply that to your synth too. A radio module will pick up the spark just fine, especially if you attach an antenna.)
Is that devise UL rated?

Pelsea wrote:
Thousands of volts sounds pretty scary, but the current is fairly low.
Won't traces in an IC chip be pretty microscopic (rhetorical question drawing attention to how little current it takes ... it wouldn't take much current, especially at 100KV)?

Does the VDG produce any EMP during use? ("EMP" = Electro Magnetic Pulse). If the EMP is at a significant level, it would only take a very small current when 100KV is used to turn your entire synth rig into a large generator ... for a very (very!) brief moment in time.

hmmm.....

Then I'd need to figure out how to tell my wife about how it is that the studio stinks like baked shit.

("It's all my suff, your synth rig is totally fine honey! No problems, it's all mine ....again!")

(hides) whistlin'




Pokeout
Pelsea
Rex Coil 7 wrote:
Pelsea wrote:
Don’t give up, it’s not as dangerous as some folks here think (says the guy with students who build fire organs). To prevent strikes on anything expensive, you can build barriers of thick plexiglas and set the apparatus on a grounded metal table. There are modules built around radio receivers, such as the RF Nomad— they will pick up the discharge just fine.

Thousandsof volts sounds pretty scary, but the current is fairly low.
Yea but .....
ranix wrote:
thousands of volts will still burn out silicon and the little wires that connect silicon to chip legs, idk I don't like it. It's why we don't shuffle around our sneakers on the carpet when repairing modules
Or why we're supposed to wear grounding wrist straps when we handle a semi conductor or even a PCB with semi conductors on them. Don't bring the damned thing to my studio.
Pelsea wrote:
The instructions say people with pacemakers should stay 15’ away. I’d apply that to your synth too. A radio module will pick up the spark just fine, especially if you attach an antenna.)
Is that devise UL rated?

Pelsea wrote:
Thousands of volts sounds pretty scary, but the current is fairly low.
Won't traces in an IC chip be pretty microscopic (rhetorical question drawing attention to how little current it takes ... it wouldn't take much current, especially at 100KV)?

Does the VDG produce any EMP during use? ("EMP" = Electro Magnetic Pulse). If the EMP is at a significant level, it would only take a very small current when 100KV is used to turn your entire synth rig into a large generator ... for a very (very!) brief moment in time.


Good point--ESD (electro static discharge) is the bane of electronic parts, which is why we need to take precautions when handling them, especially if we work in a dry environment. However, once the parts are soldered into a circuit board, they are relatively safe if the board is properly designed. And since the same design principles apply to EMP protection and preventing audio noise pickup*, anything but the messiest DIY board will probably be fine. (And if you do zap one of those, it's probably good riddance.) Once the board is installed in a system grounded according to the principles I and some others here are always harping about, it would probably take a real lightning strike to blow anything out.

Nonetheless, it would not be a good idea for the kid whose hair is standing straight out to try to adjust the synthesizer. Two performers would be safest, and the VDG operator should discharge himself before touching the synthesizer (The grounded metal table I suggested should do for this.) You even need to be careful what you wear- synthetic fabrics will not always discharge completely, but cotton will, especially if you use fabric softener.

*Mostly it boils down to keeping critical traces short and avoiding loops in the signal path. The VDG puts out a good EMP, but the amplitude of the pulse falls with the square of the distance and the sensitivity of pickup is affected by the ratio of wavelength of the pulse (very, very long) to the length of the trace acting as the antenna. I suspect the real problem will be picking up anything at all.
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