Presentation: DIY digital Theremin

Its difficult to build a theremin after someone elses plans. But its much more difficult to create these plans on your own.

I know there are already some digital schematics on the web - but I wanted to create my own version. So here is the announcement.

The deadline for my V1.0 of my theremin is the 1.3.2017. Until then I want to have a circuit board and all features working. You could call it  a beta version.

Here are the main features, most of them are tested, verified and the circuit board is nearly ready to produce:

• min. 196 kSps
• 12bit DAC - even at the lowest volume every single bit is used
• standalone application - no computer or other external device neccessary
• mute detection with touching the volumeantenna - mute indicated with a LED
• one switch-encoder + 2x16 LCD display as navigation
• calibration of the playable field of the antennas
• setable tone range up to the complete piano range
• pitch correction using various scales with a adjustable keynnote
• 8 custom waveforms, made up of to 10 single waveforms with settings for: volume, frequency multiplier, phase, offset, shape
• waveform is choosed using a conrol knob
• control knob for mix of original signal and pitch correction
• Delay-control knob : controls the time on which your hand have to stay on its position until a new note is played
• Master-Volume knob
• connection for 8 ohm speaker on board
• various effects on board: Tremolo, Vibrato, Chorus, Flanger
• midi In/out, CV out [2x], USB, mono/stereo
• only 4 parts are smd the rest is dip
• all inut direct on the pcb, knobs etc. are connected to a single connecter
• size of pcb is 17x6.6cm

I am open for any ideas and sugestions. Especialy i would like to know what you would like to do with USB and Midi in, because there probably wont be any functions on that outputs in V1.0.

Here an early version, it could look like this:

See you!

Hi Curby,

What do your oscillators look like?  How are you acquiring the oscillator information for use in your processor?  What is your plan for linearizing the pitch field?  How are you dealing with oscillator thermal drift?

"mute detection with touching the volumeantenna - mute indicated with a LED"

Interesting feature, but it might make players nervous?  Perhaps put a timer on it, so players have to touch the antenna for > 1 second or so for it to toggle?

Digital gives one the opportunity to perform more elaborate linearization, as well as mains filtering, and sizing / offset, of the pitch field.  

I'm probably in the minority here, but some kind of clear and responsive pitch display is fairly easy to do digitally, and I believe this alone can set digital Theremins apart from their analog kin.

My advice is to not make the mistake of the Theremini, where the emphasis is clearly on musical synthesis, with the capacitive sensing a distant second. IMO it's all about the C sensors.  The challenge is to keep both the resolution and the gestural bandwidth high, otherwise playability will suffer.

Well yes, that could make some players nervous. Maybe i should implement a double-touch, like a doubleclick.

In this early version I'm using semiconductor oscillators with only a glimmer C. I mix to frequencys with a flipflop. I additionally thought about measuring the fix oscillator to notice temp. drift. Maybe, but for the moment i has to work with this basic circuit.

My processor is measuring the frequency of both oscillators, but its all relativ. For an example the start position is about 4kHz and the end position is about 6kHz. Then the current value (hand position) is set to a linear relationship between these two frequencys.

"In this early version I'm using semiconductor oscillators with only a glimmer C. I mix to frequencys with a flipflop. I additionally thought about measuring the fix oscillator to notice temp. drift. Maybe, but for the moment i has to work with this basic circuit."  - Curby

Any idea on what the gestural bandwidth will be?  Like if you put a variable speed fan near the antenna and looked for the -3dB point. For instance, the Theremini bandwidth is around 2Hz, and I think this is too low (slow response) for precision playing.  See this thread:

http://www.thereminworld.com/forums/T/28554?post=206041#206041

What are you doing to linearize the pitch field?

I hope to understand your request. Wenn OSC1 = 250kHz and OSC2 = 250.6kHz, the start difference is 600Hz.

When the antenna goes towards the hand, the difference is getting bigger. In my testunit is used a start difference of 4kHz, going up to 6-8kHz. In this range it is possibile to detect up to 2700-4000 Handpositions. Of course its not linear, but I guess that will be enough resolution for precise playing. Otherwise I have to change my circuits and methods.

The difference frequency will react quite quickly, but the method you use to determine the hand position may not if there is a lot of averaging or digital filtering going on to obtain the pitch number.  The resolution you are getting is only 11 or 12 bits, which IMO is barely adequate for pitch use.  It seems you are building something very similar to the Theremini.

Well if you have 50cm/20inch play field and 4096 positions, each position is about 0,1mm/0,03inch. For the first release thats clearly enough in my opinion.

But yes I am already thinking about a finer resolution.

I look forward to see that instrument played and judged by a renowned classical thereminist. Most of the latter tell us that the Theremini is not at all playable (too much latency, bad volume response) and that the other existing digital approach, the Open.Theremin v3, is already not bad for its low price (<100€). Thus, a new digital development has also to be competitive in terms of precision playability, and musical expression (width, resolution and dB-linearity of the volume field).

Gadgets like autotune/pitch correction, auto-vibrato, etc. are only for unmusical idiots and should be avoided if you want to be taken for a serious theremin builder.

Gadgets like autotune/pitch correction, auto-vibrato, etc. are only for unmusical idiots and should be avoided if you want to be taken for a serious theremin builder."

 Hard words. But it will we included because it is possibile. You dont have to use this features .

Dont forgett I am talking about a first version. Maybe after that all will be discontinued..

"Well if you have 50cm/20inch play field and 4096 positions, each position is about 0,1mm/0,03inch. For the first release thats clearly enough in my opinion."  - Curby

If each position is laid out relatively linearly within that 50cm field, and you aren't doing any fancy math on them, then perhaps 12 bits are enough. Dithered or noisy bits below that would probably help if they average to finer resolution (the ear can tolerate a certain amount of FM without hearing it). The general problem is that the positions aren't linear, so you need a bunch more to avoid hearing the steps, and so you can do linearizing math.

"Gadgets like autotune/pitch correction, auto-vibrato, etc. are only for unmusical idiots and should be avoided if you want to be taken for a serious theremin builder."  - Thierry

I think they're OK to include.  The problem is they tend to show up in otherwise crappy Theremins (the Theremini) as turd polish - a case of guilt by association.  If the basics are covered well I don't think anyone would complain about having them in there even if they never use them. But the basics (resolution, linearity, gestural bandwidth, mains hum rejection, etc.) usually get short shrift these days, in favor of bells and whistles.