Theremin Distance Increase

So I am trying to build the University of Glasgow theremin.

http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E9/

I've made a couple, but only used the first part (up until the 4098) so that I get a nice square wave coming out of it. The circuit works fine, but the range that I get so that the changing oscillator is actually affected is only 4" max.

At one point I had about 2ft which is perfect. It lasted for about 2 minutes and then went back to its old self again.

For my antenna I have tried a telescoping antenna as well as copper tubing that was recommended. How can I increase the range??? This is for my senior design and it would be nice to have something that works well (like it did for a couple minutes) rather than something that just works.

I'd appreciate any ideas you guys would have.

Thanks, Manny

btw, I'm making air drums

I'm sorry but you did not understand the principle of the Glasgow theremin. Its pitch frequency range is much too big for using the tachometer output as an audio signal. It is intended to go through a discriminator in order to get a pitch control voltage for driving a vco which will give the final audio output.

So taking the 4098 output directly as an audio signal is not a good idea.

If you want to build a simple pitch only theremin you should rather take Art Harrison's Minimum Theremin.

Why only do so much people fall for this experimental Glasgow project which has rather no practical value??? *rolleyes*

[i]"Why only do so much people fall for this experimental Glasgow project which has rather no practical value??? *rolleyes*"[/i]

LOL! I dont know, Thierry! :) .. Probably the same reason we elect morons to govern us? - (with the exception of America, who seem to have got it right this time ;) .. perhaps because we dont understand what they are on about, and we get fooled into thinking they are cleverer than us! *rolleyes*

I think TW should remove the link to this "Theremin" - it is not worth looking at! - Rather have a link to the Smirnov (http://asmir.theremin.ru/tsensors_sch.htm) site which gives useful ideas and schematics for both conventional and voltage control Theremin 'modules'

Soho - my latest (and LAST!) comments on the Glasgow "Theremin" are Here (http://www.thereminworld.com/forum.asp?cmd=p&T=3925&F=1&p=2)

Your particular problem cannot be solved - Thierry is right - you do not understand anything about the circuit you are working on! Throw it away and buy a kit! ... Or REALLY study the Glasgow Theremin schematic and the extensive postings on this subject made here, and when you understand, you will at least have advanced in your knowledge of electronics - You will then decide to throw away this Cr*p Theremin and either design your own or build a kit!

I'm using a microcontroller to read the number of pulses within a time frame. I'm not actually using it as an audio signal.

[i]"I'm using a microcontroller to read the number of pulses within a time frame. I'm not actually using it as an audio signal."[/i]

In this case you may find the 2nd last posting on this page. (http://www.thereminworld.com/forum.asp?cmd=p&T=3939&F=3) helpful.

I suspect your problem is due to drift / interference on the oscillators - the 4093 thresholds are poorly defined, and having a seperate 4093 for each oscillator only makes matters worse. You need decent highly stable oscillators.. You MIGHT get away with TS555C's if you use the CV input for tuning (you CANNOT get stability if the tuning resistance is connected directly to the antenna capacitance - potentiometers are not designed for this - they have high capacitance which is not stable) But best bet would be a LC oscillator such as the Smirnov (http://asmir.theremin.ru/tsensors_sch.htm) or Moog designs.

[i]"I've made a couple, but only used the first part (up until the 4098)"[/i]

Presumably you are not fitting the 4098? there is no need for this!

Get rid of the 4070, and replace it with a 4013 -connect reference oscillatorto CK, variable oscillator to D, tie S and R low.. Take the Q output to the MCU... This will make a huge impovement to the 'heterodyning' stage, as there are no nasty 'sum' frequencies to get rid of.. These frequencies (out of the 4070)need to be filtered away (the R+C) and level discriminated by the following schmidt (4093) gate... The problem is that the TC of this R+C and the narrow hysteresis of the 4093 makes this circuit highly frequency dependent. Using a 4013 eliminates all these problems. (ok - I am biased, as I think I possibly invented the 4013 scheme - but whatever.. it IS a MUCH better way to get the difference frequency from two digital signals)

That's a really good idea. I wish the parts shop was open at this hour. I'll have to try it later. And you are right I'm not using the 4098.

When they are set to the same frequency (with nothing around the antenna) they are 180 degrees out of phase. When I bring my hand toward the antenna to disturb the frequency and back away again I would assume a "random" new phase relation but it always goes back to the 180 degrees. I knew they would interfere with each other, but I didn't think they would "lock in" like they are. I'm going to talk to someone tomorrow about a variable frequency antenna, but I think/know this problem can be solved with the circuit design considering I bumped something and had an excellent range for a little bit.

You have been very helpful, Thanks!

[i]"Why only do so much people fall for this experimental Glasgow project which has rather no practical value??? *rolleyes*"[/i]

Indeed.

Simple rule about college projects: [i]Commercial viability is seldom a design criterion.[/i]

This does not just apply to theremins. (youtube example (http://www.youtube.com/watch?v=30KKmErrOtg))

Ah, where do I begin?
"Hey Honey, I think I'll get that Mosquito Mask Fashion Head Wear by 'Swat-It!' that you have been hinting about for your birthday!"
"Oh, thank-you Snuugums! I was thinking that you would look good in the Half-Emasculated SpikeWare From 'Macing One Ball' this fashion season!! Uh-Huh, Uh-Huh! I bet we'll be the best looking couple at coven!"
Gordon! He finds the best!

Good Luck!

teslatheremin