Proximity Control

[Jaicen_solo]

Ohh, look at me. Postaholic tonight it would appear.
Anyway, I found this schematic for a proximity alarm using a MC14093 chip and MOSFET.
I was thinking this could have applications for use as a 'probe' style control device (Mr Hammer may have an idea where this is going).
Anyway, i'm planning on breadboarding it next week with the intention of using it to drive an LED. The thing i'm worried about is minimizing RF interference into surrounding pedals, does this look like a problem??

*b

[The Tone God]

Link/schematic ? It is hard to comment on something when we don't know the details.

Andrew

P.S. I have already been where your going.

[Jaicen_solo]

Oh dear, see what happens when fingers are flying!

I guess I forgot to paste in the link, here:

http://www.mitedu.freeserve.co.uk/Circuits/Alarm/radiowavealm.htm

If you have been where i'm going Andrew, any help you can give would be great! Did you get RF interference problems like I was expecting?? I'm worried as to how stable it'll be as well.

[Mark Hammer]

Seems to me that it is rare that commercial pedals are tolerant of anything over 50khz or so.  Even when there is no deliberate attempt to "tame the treble", one often sees feedback caps in op-amps intended to set an upper frequency limit of 70khz, or 50khz, or 30khz.  All well above the hearing range, but intended to maintain stability and immunity to interference.  I'm far from being any expert, but I would think that having well shielded boxes and cables would make your concerns minimal.  The police, on the other hand...

A question:  Is your intent to have variable proximity control, or simply on/off control?

[Jaicen_solo]

I'm going for a variable proximity control. I know Z did it first, but I guess someone has to innovate. At the end of the day, the theremin was invented 70 odd years ago so it's not too big a leap. I just think it would make an excellent alternative to wah treadles which I can never get on with really. I also want one in my guitar to control a LP filter
As for the police, i'm sure it's not going to be a problem. I've built FM transmitters before which had very limited ranges, but did interfere with my single coils. Besides, it' not going to connect to the mains.

[Dave_B]

I'm going for a variable proximity control. I know Z did it first, but I guess someone has to innovate. At the end of the day, the theremin was invented 70 odd years ago so it's not too big a leap.

I'm not sure if this helps, but Paia is offering their Theremax theremin manual as a free download.  http://paia.com/
After looking at the schematic, I'm not sure I need to get involved in proximity stuff.  It looks like a long way from the antenna to the output jack...  :shock:

[Jaicen_solo]

Haha, yeah i've thought that too.
There's  page somewhere with loads of layouts and schems for theremins like the Theremax (including some updated versions). They're actually not that hard to understand really, most can be boiled down to three distinct sections.
However, i'm not looking for a theremin per se, just the proximity detector circuit. On the theremax, I believe (from memory) this is formed from the 2N4124 transistor and the group of components in the top right hand corner of the schematic. The outpupt of this section can be used via a 2N2222 to drive an LED for instance.  It really is that simple. Getting it to work is less so! The Theremax has a lot of extra components in this design to keep the oscillators stable and free from interference, but I think its overcomplicated. That's why i'm avoiding inductors, as I think they make the circuit less stable. Having said that, I don't recall seeing transformers used as loads and inductors simultaneously, perhaps that's to help with stability.
Either way, I think in this application, CMOS is the way forward.

Tell you what though, I do fancy the Paia vocoder.....

[The Tone God]

This looks alot like the simple theremins post around the web. Two oscilators with one varied by the user with the difference outputed. The only real difference is the frequency it is running at.

Intial thoughts are basically range related both for the input and output. I don't know how sensative this circuit will be. My expereince is that the higher the frequency the less sensativity there is. On the output side starting with such a high frequency there might not be enough variation in frequency to adjust the LED's brightness through out it's range.

These are just some of my thoughts. It is a simple enough build that you throw it together and see how it work for real instead of us yakking about it here.

There are other threads on this topic. In one of those threads I stated at this time I was not prepared to release my designs to the public. I will say that personally I went in a different direction then this type of design. I would also stay away from designs with coils and the like. Too much B.S.

Andrew

[Jaicen_solo]

Thanks Andrew, that's pretty much confirmed my initial thoughts on this circuit.
I thought the frequency is quite high, but since it's working on the difference between the two, I think it shouldn't be that important. Another benefit I was thinking was that the high frequency would make for better resolution.
Basically, It is similar to simple audio theremins but that's intentional. I want a one-chip solution Coils are not where it's at at this point.
I think you're right about it being simple enough, i'm gonne breadboard something next week hopefully.
Thanks for your suggestions Andy. I'm not looking for all the answers but I appreciate any help you can give. I appreciate that you don't want to just give away all your work, especially if you intend to market it at some point.

[Dragonfly]

...as far as working on a proximity control, you might wanna do some research on "Hall Effect" ....


hope this helps,
   andy

[Jaicen_solo]

Now that is interesting. I've heard of people using induction of human body parts, but never in this type of application. I'd guess it would be prone to interference though.