Proximity Control and the Ghost Dance

[soggybag]

Tim Escobedo added an intriguing note at the bottom of hte schematic for the Ghost Dance. Anyone care to discuss this one. I have seen a few ocsicllators made from a pair of inverters or even a single invert.

I'm not quite sure where you would connect a capacitive plate to change the frequency or how you would use the output to control something?

[RLBJR65]

I asked once, I could not figure it out either, played around with the example oscillator on the spec. sheet no luck.
I had some success using the LFO? from Craig Anderton Tremolo. http://www.generalguitargadgets.com/diagrams/catrmsc.gif It uses 3 inverters of 4049 (4069 works re work the pinouts) and an LDR but could never get the correct sweep. Maybe someone will have a solution this time.

Richard

[soggybag]

I think there is a very simple ocsillator that can be made from two inverters and a cap. I have also seen one made from 1 inverter and a cap. The size of the cap determnes the frequency.

I would guess that a capacitive plate would act as a small cap?

[Paul Perry (Frostwave)]

You could replace the variable resistor by a LDR, and have a light beam focussed at it, and waggle your foot in front of the beam. That would be 1,000,000 times more stable & easier than trying ot get any kind of RF shit happening, believe me!

[The Tone God]

I would guess that a capacitive plate would act as a small cap?

Actually more specifically the plate just becomes a antenna and you become the cap. I found that these types of circuit offer lousy range. Particularly if you want to use footware.

You could replace the variable resistor by a LDR, and have a light beam focussed at it, and waggle your foot in front of the beam. That would be 1,000,000 times more stable & easier than trying ot get any kind of RF shit happening, believe me!

I almost agree. It doesn't solve all the problems but it comes close and is in general easier to implement. As for that "RF shit" don't knock it if you don't know how to do it right.

Andrew

[soggybag]

The Zvex pedals seem to have this type of thing happening very well. People have been making theremins for years that work well.

The LDR would be much easier but it seems it would be harder to operate. Ambient lighting would effect it.

With the RF oscillator would you have it charge a cap, high freqencies might produce a higher voltage?

[Paul Perry (Frostwave)]

As for that "RF shit" don't knock it if you don't know how to do it right.

Fair enough, Andrew! I'm the first to admit I'm not an RF guru! but, I know enough (from building theremins & doing VHF antenna design) to have an idea of the many ways one can get into trouble. To say nothing of the fact that it might not always be a good idea to have a capacitive antenna plate spraying around RF itself on stage.

If anyone wants to have a go at the led-ldr beam setup, the choices are:
1. reflection of beam to a sensor nearby, versus interruption of a beam

2. unmodulated light source (meaning you will have to arrange things optically to exclude as much extraneous light as possible), versus a beam modulated at say 100KHz to discriminate against stray light. (the sensor here will have to be a photodiode to get the frequency response).

For an introduction to practical RF, i suggest Bob Carr's books or the ARRL Handbook (older copies are better, from when hams built all their gear from discrete components!)

[troubledtom]

As for that "RF shit" don't knock it if you don't know how to do it right.

Fair enough, Andrew! I'm the first to admit I'm not an RF guru! but, I know enough (from building theremins & doing VHF antenna design) to have an idea of the many ways one can get into trouble. To say nothing of the fact that it might not always be a good idea to have a capacitive antenna plate spraying around RF itself on stage.

If anyone wants to have a go at the led-ldr beam setup, the choices are:
1. reflection of beam to a sensor nearby, versus interruption of a beam

2. unmodulated light source (meaning you will have to arrange things optically to exclude as much extraneous light as possible), versus a beam modulated at say 100KHz to discriminate against stray light. (the sensor here will have to be a photodiode to get the frequency response).

For an introduction to practical RF, i suggest Bob Carr's books or the ARRL Handbook (older copies are better, from when hams built all their gear from discrete components!)

i have built theremins but i have not designed one from scratch yet in do to paul's wisdom/antiwisdom/bewares
       keep it real my brothers
               peace,
                 - tom

[Paul Perry (Frostwave)]

I hope I'm not discouraging anyone, building a theremin (whether from a kit, or from a design on the web, or from scratch), is guaranteed to be a learning experience!!!!! one that you couldn't get from college, no matter what you paid.

[spudulike]

I hope I'm not discouraging anyone, building a theremin (whether from a kit, or from a design on the web, or from scratch), is guaranteed to be a learning experience!!!!! one that you couldn't get from college, no matter what you paid.

I'm very interested in building a theremin - I'm going to have a bash at THIS one next week. Any ideas how useful this would be as an effect controller ?

More schematics at ThereminWorld .

[soggybag]

Lookin through the schematics at Theremin World, thanks for the link sudulike, I found this which looks like it could be used in a stompbox project.

I'm not really sure but it looks like this uses two oscillators, the first two inverters on the left, to create a pitch from the beat frequency. The upper oscillator seems to be variable through the anttenna, while the lower is adjustable via a pot. It seems for the purpose of making the ghost dance adjustable via the anttenna, we could just use the upper oscillator and have it feed into the gate of a FET acting as the variable resistance?

[Paul Perry (Frostwave)]

Notre the 100pf cap at the input..... the question is, will your leg (or whatever) make enough difference to get a useful range of variation?
Which brings out why theremin type devices usually have two oscillators & heterodyne them to get a wide frequency range with small capacitor difference (even if the output is going to be converted to a control voltage, whihc you can do with a 'tachometer' type frequency to voltage converter circuit).
And, another thing on the circuit fragment there... nott the two oscillators have the same pin numbers, implying they are on different chips. Why not put them on the same chip you ask? Because, if you do, they will interfere via the common power pins! So you have to spring another 50 cents for a second chip.
If you DO want to use a single oscillator, then you could use 'slope detection' (a tuned circuit just slightly off from the oscillator frequency, sot hat as the freq changes the output signal level changes). What can go wrong? Well, for a start, the oscillator freq will vary not only with your leg, but with temperature, humidity, and possibly phases of the moon. Be prepared for radio station pickup as well.

[soggybag]

Perry, it sounds like you are calling this impossible or nearly so?

It seems that this has to work without too much trouble. I've seen several theremins that would fit into a 1590B box and the Z vex probes seems to work well enough to be sold comercially. If the plate picked up radio noise it might not matter if the whole proximity detector was isolated with an LDR.

Of course I'm not an expert and really only have the slightest clue as to what is happening. But I do feel that that the problem is not as difficult as it looks. I'm willing to bet that Z has found a simple and elegant solution with a minimum of parts.

[The Tone God]

...the question is, will your leg (or whatever) make enough difference to get a useful range of variation?

Thank you for confirming my thoughts on this and pointing out other the problems. I am also sure those interested would have used the function and found others with the same experience and maybe more information.

Perry, it sounds like you are calling this impossible or nearly so?

I don't think Paul is saying it is impossible but that it is difficult to do for those without the correct knowledge like DIYers and not those crazy hams. There is alot that has to done correctly in order for it to work correctly.

If every DIYer built the same circuit the same way, meaning same physical circuit construction, then the amount of build assist posting would be much lower here. Of course this would not be DIYing so instead we get alot of build assist posts that are cause by circuit construction problems like wire routing, part subbing,  control orientation, etc. What does this have to do with proximity control ?

Proximity control circuits, like audio circuits and maybe even more so, are sensitive to their surroundings and construction means. With everyone building such a circuit differently in the DIY fashion it becomes difficult to support such a circuit for those without the knowledge. Knowledge which is not discussed in common around these parts.

Paul's light sensor suggestion, I only can assume, was intended to help simplify alot of the problems for the average effect DIYer. Although those with the required extra knowledge would know how to do this in an appropriate manner.

Of course I'm not an expert and really only have the slightest clue as to what is happening. But I do feel that that the problem is not as difficult as it looks. I'm willing to bet that Z has found a simple and elegant solution with a minimum of parts.

Its funny when people say "I don't know how to do it but I don't think its hard" about things that are alot more complex then they understand or realize. The problem and sol'n are two very different things. The problem is more difficult then it seems but once you understand the problem then a sol'n maybe easier then most think.

Just my thoughts.

Andrew

[Jaicen_solo]

I've been looking at this for quite some time actually, almost as long as the Fuzz Probe has existed (in the public eye at least, i've been around a while ).
I've never seen inside one, but I have been told that the RF oscillator is a one chip design, probably using a CMOS chip. There may also be a regulator to keep the voltages stable, but that's purely speculation.
From the information i've gathered, it would seem that it is possible to increase the sensitivity of the sweep in two ways. Firstly, you can just amplify a small sweep through a rectifier to give a larger +/- DC swing. Secondly, increasing the oscillator frequencies will make them more susceptible to smaller capacitive changes.
This does bring in some small issues when the oscillators begin interfering with local radio etc, but I don't think these designs will ever output enough power for that, especially if it's well isolated.

EDIT: This might be useful too.
http://www.diystompboxes.com/sboxforum/viewtopic.php?p=120118&sid=d5297874045229d24b18bc45f24aa271

[soggybag]

I remember seeing some posts by Tranmorgifix about the proximity detector. I seemed to remember it being unresolved.

Looking at this scheme it here http://www.geocities.com/transmogrifox/ProxyOzzi.html is a little confusing. I don't understand what is going with the lower op-amp?

Looks like the upper op-amp is an oscillator whose frequency is ajusted through a metal plate that would be replace the 14p cap. The op-amp on the left looks like a voltage follower for the 4.5v reference.

From the description is sounds as if this circuit was meant to feed into another, which is not shown here, that is comprised of a PLL. The PLL is used to convert frequncy to voltage, can anyone elborate in this? It seems that this part would be esential.

I would think the oscillator here could be replaced by one made from two inverters in the 4069, with maybe one extra inverter used as a follower. I whipped one of these up from an app note last night and it seemed to work pretty well with little effort.

[Paul Perry (Frostwave)]

From the information i've gathered, it would seem that it is possible to increase the sensitivity of the sweep in two ways. Firstly, you can just amplify a small sweep through a rectifier to give a larger +/- DC swing. Secondly, increasing the oscillator frequencies will make them more susceptible to smaller capacitive changes.
This does bring in some small issues when the oscillators begin interfering with local radio etc, but I don't think these designs will ever output enough power for that, especially if it's well isolated.

Amplifying a small sweep is OK, provided there isn't any noise (from unwanted interference or low frequency random fluctuations) present.
Similarly, increasing the frequency of operation will make the theremin heterodyne product have a wider frequency range, true, but again there is no point amplifying an unstable signal. In practice, successful theremins seem to cluster around 500KHz.
So far as interference from theremins is concerned, there is probably more trouble caused by radio signals getting into the theremin circuitry. If I were building an RF theremin, I would definitely think about tuned circuits at the antenna base.

Incidentally, I havn't searched for this, but I seem to remember something here some time ago about special purpose proximity detector chips (for 'switchless' controls). That might be the way to go.

As for theremins in tiny boxes.... yeah, I've seen them! and, I've HEARD them too.... it's possible to get a theremin effect from them, but if you are playing Carnegie Hall, you'll want a Moog.

[Zero the hero]

I've built a proximity controller and it worked. It returned an almost clean control voltage but it was "weather sensitive". It didn't work in rainy days!!!!
I'll post a scan of the schematic, as soon as I'll find it...

[The Tone God]

Incidentally, I havn't searched for this, but I seem to remember something here some time ago about special purpose proximity detector chips (for 'switchless' controls). That might be the way to go.

You probably thinking of the Qprox ICs. I have addressed some of their short falls in previous similar threads. I have look at other commercial touch systems and there is no "one chip" sol'n out there that I have found.

I have played with touch technology awhile back coming up with about twenty different methods including about half a dozen full on gradiant distance detection circuits. One could build a really good stable circuit using 8-12 standard parts that you can get at Mouser/Digikey/Smallbear/Radio Hack.

Andrew

[soggybag]

Here is a link to a site that was posted earlier. It documents a theremin created using a proximity detection chip. Sounds like it might be a good solution. Though it goes against the idea of getting some use out of the extra inverters on the 4069.

http://www.paddfam.com/c2cv.html