Proximity control

[earthtonesaudio]

Hey all, I want to get a workalike of a Wah Probe going, without ordering any new parts.  I have a 4069 (close enough), so this is my candidate:


It's a simple ...simple? Make that a complicated, theremin-based proximity-controlled switch, from what I can tell.

My analysis is that the circuit goes like this (left-right): Oscillator, high pass, rectification, RC time constant, U1c makes it an on/off voltage, allowing Q1 to make a control voltage (turns the LED on or off)

If I take U1c out of the circuit, would it work as a variable LED brightness with a corresponding variable capacitance on the antenna (preferably with a foot-shaped object)? 

Thanks!

[dano12]

Might be something of interest here:

http://topopiccione.atspace.com/pjimages/TPCInvisibleTouch.sch.gif

http://thereminvision.com/sensors/schematic-10.jpg

http://www.harrisoninstruments.com/101/101_schematic.html

[earthtonesaudio]

Thanks!  The minimum Theremin schematic might be something I can use.  I actually have the others already saved on my hard drive, but I just don't have the parts on hand.  I'll see what I can do with the min. Theremin.

Fingers crossed...

[~arph]

http://www.friedair.com/images/arph-probe-schem.png

Pay attention that the LED is oriented wrong.. it must be flipped.

[Valoosj]

Arph, have you built this already? Any pics? 
I'd love to build something like this with a wacky effect in it.

[DWBH]

Well, I'm pretty sure that schematic that ~arph posted is pretty accurate 

[earthtonesaudio]

My boss suggested something cool: use the min. Theremin as a starting point, but just use a simple passive filter (say a RC highpass) on the output to ensure that the amplitude of the oscillator changes with frequency.  This would give you the ability to change the LED brightness as the frequency of the oscillator changes.

One caveat, though... this hinges on the output signal of the Minimum Theremin being linear to start with.  If it's all over the place, this definitely won't work.  But on the plus side, if it does, then you could have a Theremin in addition to a proximity control!  Just imagine a theremin wail mixed in a little with the sweep of the wah... Oh right, my wah circuits already oscillate pretty well on their own.

http://www.friedair.com/images/arph-probe-schem.png

Pay attention that the LED is oriented wrong.. it must be flipped.

This looks a little familiar...    But all I have lying around are 4069 inverters.  I doubt I can use what I have with this circuit... or am I mistaken?

[earthtonesaudio]

Okay I looked it up.  I definitely can't make a regular CMOS inverter do what a NAND Schmitt trigger does.  Looks like I'm going with the modded minimum Theremin.

[The Tone God]

Okay I looked it up.  I definitely can't make a regular CMOS inverter do what a NAND Schmitt trigger does.  Looks like I'm going with the modded minimum Theremin.

I doubt that you could as the switching thresholds are different.

I generally don't like those types of designs as you are changing the oscillator's frequency and it does not take much to get the oscillator into audio frequencies creating noise in the audio circuit.

One of the reasons I have not released any of my proximity control designs is that one of the biggest variables is the antenna design. People would be surprised just how much a minor change to the antenna can affect the performance of the circuit. To get a consistent result with a community who generally revels in its diversity would make support very difficult.

Andrew

[earthtonesaudio]

I generally don't like those types of designs as you are changing the oscillator's frequency and it does not take much to get the oscillator into audio frequencies creating noise in the audio circuit.

I'm planning on going with the min. Theremin design, but I'll be using an LED/LDR for controlling my effect.  The only way they'll be coupled is through the power supply, and I usually put some radio-frequency filtering on anything with much gain.

One of the reasons I have not released any of my proximity control designs is that one of the biggest variables is the antenna design. People would be surprised just how much a minor change to the antenna can affect the performance of the circuit. To get a consistent result with a community who generally revels in its diversity would make support very difficult.

I can especially the antenna being a big variable in this application, considering the fact that half of the variable capacitor is a person... You might need to tweak for each different user, different humidity levels in the air, shoe thickness, etc.  But trimpots could take care of most of those issues. 

It seems to me the BIG variable with antenna design is surface area.  And it's something you can't vary continuously.  You either cut your antenna down, or you get a bigger one.  Hard to tweak, for sure.


...Well, if I get one going, I plan to post it for the community (and the world, naturally).  I guess my schematic will need a bunch of caveats, asterisks, and parentheses. 

[Paul Perry (Frostwave)]

It's true that oscillating designs can bleed interference into things - but an even worse problem (in my experience) is, external interference bleeding into the sensor circuitry via the antenna.
As to the original 4049 circuit in the first post - it's not obvious to me, what is going on there.
Is the sensor plate acting as a cap to ground, and turning a HF oscillator on and off?
Is it always oscillating, with the sensor plate cap changing the output level of the RF?
Is it always oscillating, with the sensor plate changing the frequency, and at the same time, the amplitude?
And the million$ question - will it work with another manufacturer's 4049, let alone a 4069

[earthtonesaudio]

I have since ditched the idea based on the picture at the top of this post, and will plunge ahead based on the Minimum Theremin that Dano posted.  But to answer Paul's questions (regarding the schem at the top here)

I think the sensor plate is acting like a cap to ground, and the person is the other plate of the cap, attached to ground.
It is always oscillating, but touching the plate might just cause it to stop.  Not sure what *almost* touching it will do.

Million dollar question: n/a! I've seen simpler touch switches anyway.  Even ones that run on AC line voltages!  Try that with an inverter!  But I digress... 

[The Tone God]

Most of those designs work on the basis of changing the oscillator's frequency by varying capacitance. There will usually be a very small capacitor that sets the fast frequency. The antenna then picks up the external capacitance of the human body. To understand the principal look up "Kirchoff's Law". When the higher capacitance of the body comes near the antenna the oscillator will slow down increasing the voltage to the LED producing a brighter output.

There are several problems with these designs. The sensitivity is heavily based on the frequency. The higher the frequency the lower the sensitivity. The lower the frequency the more likely you will end up in audio range when the appendage approaches which will likely bleed into the audio portion of the circuit. The bleed will not come from just clock noise leaking through the power supply but will actually radiate inside the enclosure. This is one of the reasons the antenna design and tuning of the circuit will be crucial to making the circuit work and there is a good chance you won't even get anything decent from it after all that work.

If you are plan on using a circuit like this you might want to look at building the circuit in an isolated portion of the enclosure and maybe put internal shielding around the circuit inside the enclosure. Even better might be to build the circuit in it's own enclosure and hooking it up externally.

Personally I don't like the idea of varying clocks be it directly or through other sensing means. They just give lousy range, both in sensing and output swing, and are a PITA to get working right. Even popular designs that I have seen leave something to be desired range wise.

If you want more information do a search as I have posted on the topic a few times.

Andrew

[~arph]

Arph, have you built this already? Any pics? 
I'd love to build something like this with a wacky effect in it.

Nope, only breadboarded it once, worked like a charm with a plate out of PCB material (100x160 mm). Range up to about 10"

[Valoosj]

Nice. Can you put it in any circuit?

[~arph]

More or less.. with use of an optocoupler/vactrol/LDR, you can put it in place of any pot wired as a variable resistor. (two poles used) If you'd like to adapt this for pots wired as voltage dividers (3 poles used). I advise you to look at Tone God's Rock 'n Control

[earthtonesaudio]

There are several problems with these designs. The sensitivity is heavily based on the frequency. The higher the frequency the lower the sensitivity. The lower the frequency the more likely you will end up in audio range when the appendage approaches which will likely bleed into the audio portion of the circuit. The bleed will not come from just clock noise leaking through the power supply but will actually radiate inside the enclosure. This is one of the reasons the antenna design and tuning of the circuit will be crucial to making the circuit work and there is a good chance you won't even get anything decent from it after all that work.

If you are plan on using a circuit like this you might want to look at building the circuit in an isolated portion of the enclosure and maybe put internal shielding around the circuit inside the enclosure. Even better might be to build the circuit in it's own enclosure and hooking it up externally.

I plan on using the Minimum Theremin, and tuning both oscillators to a fairly high frequency, above 20kHz at the very least.  The output is the beat frequency of the two slightly out-of-sync oscillators being heterodyned by the simple diode OR gate.  All the oscillations are happening above the audio range, but I also plan on using an LED/LDR pair to isolate the Theremin from the circuit I want to control.  ...And the circuitry will be in an enclosure, and the antenna separate and insulated from the enclosure.  I imagine that will take care of any bleed-through, but I'll check on your previous posts to confirm.

Personally I don't like the idea of varying clocks be it directly or through other sensing means. They just give lousy range, both in sensing and output swing, and are a PITA to get working right. Even popular designs that I have seen leave something to be desired range wise.

As far as I can tell, the Minimum Theremin doesn't vary a clock in its operation... or are we on different pages? 

Thanks for your input.  I am certainly going to proceed with caution! 

[earthtonesaudio]

Nice. Can you put it in any circuit?

Like arph said, pretty much... the fun part comes with choosing what circuits to use.  It'd be great for controlling speed on a modulation effect, or delay level or something.

[The Tone God]

I thought about this a bit more and may have another idea that I haven't tried. I still prefer locking the clock frequency to a fixed value so I think a better way to go is to use some type of PWM. So instead of changing the frequency we adjust the duty cycle of the output that way the clock can remain at the same frequency and out of our audio.

I used a PWM in one of my previous FX-X entries called Crazy Larry. One could grab the PWM out of it and recalibrate it to fit this particular application. To vary the duty cycle a transistor tied to the outside, similar to what ~arph's schem does, can be used.

There are better ways IMHO but it could be a good DIY starting point for something interesting.

Andrew