Theremin circuit shown in this schematic diagram uses digital component, so we can call it a digital Theremin. This circuit employs logic inverter 74C04 or CD4069 hex inverter and CD4046 phase-locked-loop (PLL) IC.
The CD4069 logic inverter is operated as a fixed-frequency oscillator with frequency around 100kHz. The CD4046 is operated as a variable frequency oscillator which is adjustable around 100kHz. The exact center frequency of the on-chip oscillator is determined by R4, C2 and R3. Here is the schematic diagram of the circuit.
Digital Theremin Circuit Diagram
The frequency of variable oscillator frequency circuit can be shifted several kilohertz by moving your hand approaching the antenna since the C2 and the antenna form an equivalent parallel capacitance. The frequency of the variable oscillator should be set to the same frequency of fixed oscillator when there is no hand or human body close to the antenna.
This calibration is done by adjusting the zero control R4 pot with this simple rule: If both oscillators (the fixed and the variable) are set to the same frequency then the Theremin will produce no output (silent). This Theremin circuit will start producing audible tone if you move your hand approaching the antenna since it will shift the frequency of the variable oscillator. You can play this Theremin circuit by moving your right hand around the antenna and at the same time turning the volume knob R5 with your left hand.
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ReplyDeleteIn my research I have found that there is a mistake in the schematic.
ReplyDeletePin 10 on ic 4069 should be pin 9. Pin 10 is an output pin so should never be attacked to the positive power.
I found the original article here: https://manualzz.com/doc/1069739/the-555
Interestingly the printed circuit board diagram connects to pin 9.
Also the text refers to "connecting antenna to pin 5 (of 4046 ic)" but it should be pin 6, as shown in the schematic.
It's an interesting article. The most important thing is that a metal case, and allowing warm up time gives better performance.
Hope this helps anyone else who tries this circuit in future.
All the best.
PUNK DUCK--
DeleteSo have you built this unit with the pin corrections noted above - and does it work well?
GARY
Hell Gary,yes I have built this theremin with the corrections to the circuit as I mentioned. Do check out the article I linked to its worth reading. I believe the actual printed circuit is correct. I made mine on perfect board sort of following their layout.
ReplyDeleteIt works OK for a bit of fun. I just wanted it for a bit of recording. Mixed into my songs with lots of reverb and echo it's fine. I'm into making weird noises rather than playing melodies with it. And this circuit is cheap and simple with easy to obtain parts.
If you want a proper theremin to play melodies that's nice and stable then I'd say make a better one if you are experienced in electronics. Proper theremins are a lot more complicated! There are kits and pcbs around if you look. Or buy a Moog one! But I'm happy with $20 spent and making a noise. Good luck! Stay safe. PD😎
PUNK--
Deletemy apologies - didn't see your reply to my May 2nd post until just now. many thanks for your kind response and suggestions. yes, I am fairly experienced in electronics, so I'll finish up the digital theremin, give it a whirl, and probably test out another circuit after this one. it's all late-life fun with some 60s solid state nostalgia thrown in. ;]
best,
GARY
Good luck with it, and yes I tend to seek out fun older things too. There's a big repository of old Everyday Electronics going way back that's always interesting. And YouTubers like "Look Mum No Computer" that keep me inspired. Do let me know how you get on! Stay safe PD.
ReplyDeleteP.D. -- Gary here (from 2021). A year later, having been preoccupied with eldercare (of two maternal aunts), I just this week completed the Theremin project - and it works beautifully! I'm no Clara Rockmore, of course, but I'm planning to hook it up to my small Fender amp with synth effects and see how it sounds with Delay, Echo, Wah, Fuzz added. If you (ever) get this note and wish to see a few photos of my build (in a small, metal Celestial Seasonings tea box), let me know. For now, my thanks, since it was you who pointed out the diagram error (re pins 9 & 10) that doubtless saved me some heartache. best, GARY
DeleteHello Gary, thanks so much for letting me know. That's made my day!
DeleteThis is what the internet's for I think, good sharing stuff.
Glad you've had some more time to do enjoyable stuff after the kindness you've shown your aunts.
Have you tried effects on it yet? Echo and reverb are most excellent on it, along with a bit of tone control. I found that the wobble in my hand along with the delay, gives quite a wide sound. I've not tried a wah yet. I can imagine needing a few safety cushions needed, standing on one foot waving my arms about, haha.
I'd love to see some pictures of yours. I just appended my blogger with some pictures of mine, along with a few words gleaned from our conversation.
Here's a link:
https://monokulture.blogspot.com/2022/06/sandwich-press-theremin.html
All the best.
PD
PD--Thanks for responding! Actually, since I wrote the above, I made a second digital Theremin, this one based on electrical engineer Arthur Harrison's "Minimum Theremin" (https://www.theremin.us/). The man has his own little industry making/designing and selling Theremin kits. Anyway, I'd love to send you some jpegs of both units - to what address?
DeleteGARY
And yes, I tried it with a whole host of effects on my small 20-watt Fender amp - beautiful & sometimes hilarious stuff with wah, delay, fuzz and other combos. GARY
Delete