A digital Theremin project from GLA.ac.uk

Ive made this smaller to fit
http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E9/cir2.gif
I did build this like 3yr ago but it blew up, took out one corner of a chip. So figured ever it was a bit wrong  or i got lost over time and put the Power to the wrong pin. 

Wonder if any one else has built this, I do see bits of this circuit else were and having different values (did see one with a Z80 CPU) 

Im not 100% sure how this works, your hand is like a capacitor to the Ariel. So what happens if you hook a Cap to it and then to earth or the other side of the Power.
Is there any way to change it for a Resistor change, so i can turn a knob on a Vairable Resistor to change the volume controls.

[Sorry for my Grammer, Wile Jumping around, and the poor spelling. Dyslexic and trying to find ways around improving my Grammer/Thinking/Spelling]

Hello Angel,

Some theremins are designed with focus on sounding good, others for the over all response or tricking digital into thinking it is analog and then there are those that look pretty. A University student just needs a grade so it must look good on paper but is never intended to work as most would hope for. This is a budding students design that he might one day improve upon but for now it might bring you nightmares so use caution before you invest to much time.

Christopher

Edit: Post a link of a theremin video from YouTube so I might get an idea of where you want to go. Also when you mentioned 3D Graphic Equalizer I almost thought those were the key words I was looking for but it did not pan out.

OH .. dam lol thing cost me about £100 in parts over time oh well

So i guess 

this should be more FIRST role model to build.. Simple :( 
shouldnt of dreamed tooo big too  fast

Thank you.. 

3D Graphical Equalizers is done over Pitch/Volume/Time
Pitch would be Colour (Blue low tones, Red/White High)
Volume will be how high the Light gose up (x,y)
Time will be how far it goes back (z)

A few things need to be noted about the "Glasgow Digital Theremin"

1.) It is utter rubbish! - This "design" has no redeeming features - it consists of RC oscillators with no compensation / equalization of any kind, and the following circuitry is no better!

2.) It is not "Digital" - Sure it uses "digital" ICs (CMOS logic gates) but the way most of these are being used are not as binary computation elements, but in a quasi-analogue (mixed signal) way - The only binary functions implemented are the XOR and counter to derive the difference frequency and devide this.

3.) Following derivation of the difference frequency, this frequency is converted to a voltage (back to analogue) and used to drive a voltage controlled oscillator (analogue).

You are far better off with Art Harrison's Minimum theremin* - it also uses CMOS, and it is also a "mixed signal" rather than a "digital" topology.. But it has the advantage that it directly produces audio without needlessly going through the utterly wasteful and absurd frequency-to-voltage followed by voltage-to-frequency  conversions..

The frequency-to-voltage followed by voltage-to-frequency  conversion topology works extremely well and has many big advantages IF done correctly (this topology allows one to tune the audio independently to the antenna circuitry, Allows one to select whatever pitch field sensitivity you want, allows simple register switching and allows multiple voices and voltage controlled filters etc to be incorporated IF done correctly) - But to do it correctly one needs to produce a linear voltage from the "front end" and have exponential VCO's etc driven from this voltage.

The Glasgow theremin does NOTHING correctly and is a useless waste of components! - Real sad IMO that perhaps the most noted "contribution" to theremin construction from the UK is this utter garbage (not to mention the fact that the academic contribution and even the maths in the "thesis" is utterly flawed and hardly worth the paper it was written on)

The sad thing also is that this work BY STUDENTS seems to be regarded as authoritative - it aint! - Its a STUDENT THESIS! A far better theses has been presented here at TW in the last year by American students -

Being half Scottish and half Dutch (My father was from Glasgow) I feel that no true Scotsman would produce such rubbish! - ;-) ..

Throw out the Glasgow theremins - bin them - delete them from TW.. Or at least mark these as not worth reading or building! - How many more times are constructors going to pull this circuit from TWs repository and attempt to build it ? Fine if they are warned..

*If you actually want a somewhat playable theremin, the standard RC front end (as the Glasgow and Art's Minimum theremins have) wont give you that IMO... For £22 you can buy the Jaycar Theremin which is a great started project IMO.

" thing cost me about £100 in parts over time " - You are paying way too much for your components!

Fred wrote:

A few things need to be noted about the "Glasgow Digital Theremin"

1.) It is utter rubbish! -

Fred,

Every once in a while I enjoy being reminded why you are one of my favorite people! 

"I enjoy being reminded why you are one of my favorite people! " - Peter

Thank you for those really kind words, Peter.. At least my sulpherous smell doesnt put everyone off! LOL ;-)

[Just saying the above reminded me of Arthur C Clark's "Childhoods End" - Perhaps im not a devil - just an alien! ;-]

Fred.

mm ok, the main reason for the glasgow one was that i kind of hoped it was be easy with just using IC, i didnt read up on the IC as the circuit was there and figured that it would be ok, cheap and easy way to make it.


Digital: " To download our digital theremin circuit, designed and built by Lindsay Reid and Brendan Dougan for a final year project, click here. "
that is why i said it was Digital as the MAKERS said it was Digital ok.. Took Face Value that someone correct. Sadly i did try and find the FQA on this but its gone :'( 

http://www.theremin.us/Glasgow/glasgow.html

Rule 1:

NEVER believe a word anyone says about the theremin or what any theremin manufacturer tells you, until you have checked them out! -

There are dozens of high school and university projects claiming all sorts of things, because the students dont know they are talking rubbish, and the lecturers are too incompetent to realise they are talking rubbish and correct them..

Fact 1:

"Analogue" and "digital" are words most people dont understand..

There is a whole "industry" which relies on ignorance, and fights anyone who tries to dispell this ignorance - Coupled with this, most people are too lazy or disinterested to bother seeking out the facts to obtain understanding.

Most of the time none of the above matters - But if you get into building your own kit, it becomes important - You need to understand in order to make the better choices and get the best from what you make.

The real question comes down to how much you are willing to invest in your project, and how you get return from this investment.. If you are only interested in having a theremin, you are better off buying one - or alternatively buying an easy kit.. Otherwise you are gambling your "investment" - You may end up with what you want for cheaper than you could buy it - or you may end up with a pile of rubbish.

If your aim is to learn, then, and IMO only then, is the investment possibly sensible - But start by learning the basics FIRST before you spend any money! - Study basic electronics to a level where you can understand exactly what the circuit you intend to build does.. And study up on facts related to what you intend to build, to see if it does what you want / need .. Only then buy the parts!

The last time I went to the doctor he said he needed to do a digital...but after he was done I would swear it was an analogue. Maybe I misunderstood?

For me it is natural (nature) verses un-natural, then that raises other questions? Digital functions with square waves but does not necessarily mean square waves are always digital, just square.

Digital is limited by logic..finite, I listen to nature.

Christopher 0-:

I said:

"Analogue" and "digital" are words most people dont understand..

Christopher replied:

"For me it is natural (nature) verses un-natural, then that raises other questions? Digital functions with square waves but does not necessarily mean square waves are always digital, just square."

"Natural" and "un-natural" - Oh hell - The number of times I have engaged in argument over these words.. (mostly with judgmental moralists, including my father who regarded "un-natural" as "sinfull" - And un-natural was anything he or his god didnt like - always "strange" to me that rarerly, if ever, are peoples personal 'likes' and 'dislikes' different to thier gods 'likes' and 'dislikes' ;-)  Even at £1 a time, I probably wouldnt have any financial worries now if I had been paid.. But the bottom line is this, like it or lump it, NOTHING is "un-natural" .. Right down to QP , everything which can happen does happen - everything which does happen is determined by nature and is therefore "natural", and, as everything which can happen does happen, everything which happens is all that can happen! - so everything is "natural" ! ;-)

Let me explain how I think about "Digital" "Analogue" and "Mixed signal" - my "understanding" or "perspective" if you like:

Binary signals:

There is no difference between a square wave and a binary ("digital") signal in terms of its voltage levels -  Generally, one thinks of digital in terms of binary, as in, "two state". I will ignore for a moment the fact that there is no such thing as a truly "binary" signal, that "analogue" "invades" everything (there is always a transition slope when a physical device goes from one state to another) then every square wave can be regarded as a binary ("digital") signal - it has 2 voltage states, one being regarded as "low" or a logic 0, and one being regarded "high" or a logic "1".

There is no difference between a square wave generated by a couple of transistors in a multivibrator, or generated by feeding a sine wave into a comparator (as with the Theremax) or generated by a pin on a MCU driven by software which flips this pin from "1" to "0", in terms of the fact that these are all signals which have two possible amplitude states only.

However, there is some murky water - "water" which, IMO, makes defining "binary" as equivalent to "digital" somewhat inaccurate..

Mixed Signals:

In terms of amplitude, Binary signals are constrained to two levels - However, one can have a square wave which has an entirely unconstrained frequency - This can probably be easiest seen (in terms of theremins) if one takes a VFO whose frequency is changed as a function of antenna capacitance, and can be ANY value within its designed range.. The amplitude (level) and shape of this waveform may vary, so its "Y" axis can be analogue - Its frequency can vary, so its "X" axis is analogue..

Now, if we take the above VFO signal, and feed it into a correctly designed comparator, we get a square wave out from this comparator - This square wave has BINARY output levels - All analogue data from the input signals "Y" axis (the wave shape and amplitude levels) is lost.. However, the input signal analogue data on its "X" axis (its frequency) is retained and "duplicated" on the square wave from the comparator, whos "X" axis will still be "analogue".

This, to me, is a "mixed signal".

Mixed signals can be processed by binary computation elements and still retain the analogue "X" components - This processing can be simple (XOR "heterodyning" is the simplest example I can think of) or more "complex" .. (see my "Mixed signal waveshaping" post on Element-14)

"Mixed signal" covers a huge area of essential electronics and theremin implementations - The Theremax square wave generator is mixed signal, the E-Pro deviders and XOR are mixed signal.. Neither of these theremins are digital! - They are MIXED SIGNAL, or at least employ some mixed signal elements... And of particular note is that these "mixed signals" are directly involved in the actual audio generation or audio signal path.

So - Whats "Digital" ?

Digital, to me, for practical purposes, is where both axis (X and Y) are numerically constrained - If one has a VFO and feeds this into a circuit where it is processed, and where (for example) the VFO frequency is "chopped" into 1 cent "quantities" , and the analogue "Y" data is discarded, and from this an audio waveform is constructed, then one has a digital system - All analogue data has been "quantized".. The required data has been extracted from the input signal/s, converted into numerical (Digital) form, processed by digital computation elements, and used to produce audio output based on the input data.. All aspects of the processing and output data are constrained to the resolution available to the processor and its components, both on the "X" and the "Y" axis..

The above "constraints" were a problem in the past - Processor speeds and bit depth made it difficult or impossible to cleanly resolve pitch data without "zipper" effects, and there were many problems - But modern processors and FPGA's etc are probably now capable of implementing a theremin where numeric constraints are below the level where they can be noticed.

I have not yet seen a digital theremin on the market (not saying there arent any - but I aint seen any that I know of - perhaps there may be some which are pretending to be analogue !) - Dewsters theremin is the only demo of a truly digital theremin that I have definately seen.