Theremin World Recent Forum Posts

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"Is this with the old or new AFEs ?" - André

The testing was done with the old AFE and old 1mH pitch coil, but it was developed with the new AFE and new 8mH coil. The AFE isn't important for this feature, the software and FPGA load are where the action is. I'll release these new loads soon, including an updated FPGA load for the previous kits.

Let's Design and Build a (mostly) Digital Theremin! (by André)

Is this with the old or new AFEs ?

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

DPLL Lock Testing

I instrumented the software to increment a 32 bit wide location in memory every time a bad lock condition was detected and dealt with. The D-Lev librarian and HCL commands (Hive Command Language) enabled me to query the address location and read the value. At power-up the value was 1, and with normal use the value never changed. Even with two hands on the heavily insulate pitch plate of my lab unit there was no unlocking detected. Light brief touches to the conductive plate produced several hundred unlock intervals; the duration of each interval is 1 / 48kHz = ~20us, so these events lasted on the order of 15ms or so, and they were not noticeable to me. Longer touches of the conductive plate produced much longer and obvious unlock states, on the order of 150ms or so. I'm pretty happy with these results as they allow for a much wider reliable operating zone for the field oscillators.

Building a theremin and learning some electronics along the way. (by dewster)

"Thanks i bought a couple of 74hcu04 and will give it a try" - MaltWhiskey

Of the different logic families I tried, AHC worked the best, though I didn't try HCU.

This oscillator benefits from a high speed inverter (to minimize phase error) with sufficient gain (buffered) and well-centered threshold voltage. AHC fills this bill quite well.

"BTW: how can i inline the pictures instead of clickable links?"

1. Make a photo album here (Media | Photo Albums) and save your picture to it.
2. Copy the link to the picture (not the thumbnail).
3. Click the "insert an image" button and paste the link (with optional size constraints, I usually just use a width of 800 or so).

Building a theremin and learning some electronics along the way. (by MaltWhiskey)

Thanks i bought a couple of 74hcu04 and will give it a try

BTW: how can i inline the pictures instead of clickable links?

Building a theremin and learning some electronics along the way. (by dewster)

Yes, welcome to the club MaltWhiskey!

"Than i figured 3v3 would probably not be good enough, i need a stronger electric field."

If I were building an analog Theremin I'd probably go with Buggin's amazing oscillator:

http://www.thereminworld.com/forums/T/33275?post=221506#221506

With the right coil you can easily get 250Vpp or more at the antenna with a 3.3V supply.

Also: voltage regulation of the oscillator supply is more or less mandatory for stability. For some oscillators it is critical, but all oscillators benefit from supply regulation to one degree or another.

To view stability and sensitivity on your scope, set the delayed sweep to the inverse of the mains frequency. E.g. for 60Hz use 16.666ms, for 50Hz use 20ms. This will put a zero at the mains electric field, and allow you to observe things without all of the jitter that it imparts. It's kind of like heterodyning.

Building a theremin and learning some electronics along the way. (by JPascal)

Welcome to the club. The Clapp oscillator is a very good choice, high Q due to the air coil too. Temperatur stability and pitch response behavior will be fine.

Building a theremin and learning some electronics along the way. (by MaltWhiskey)

https://imgur.com/C9B7vwY

https://imgur.com/8cRuKjw

https://imgur.com/4fGhCkE

https://imgur.com/Hl2KInz

Building a theremin and learning some electronics along the way. (by MaltWhiskey)

I had a week off, so i thought lets build a theremin how hard can it be

I figured i go buy a brass rod at the hardware store and i had a box laying around. Turns out it’s kind a hard to bend a 6mm solid brass rod. And it’s also hard to cut a thread on them. But now i can do both so lessons learned. Three days well spend….

Well i wanted to get it working fast so i thought put in an esp32 that has capacitive touch, so i can use my antennas.
It kinda worked, i got 7 different distance readouts for volume and 5 for pitch….
So thats a fail…

Than i figured 3v3 would probably not be good enough, i need a stronger electric field. So i did some research and found the d-lev. With some nice instructional videos how to make air coils. So i designed a coil holder in fusion 360 and hand wound two of them. Also liked the led pattern so i drilled some holes in my box and put in some adressable leds.

I’m not an electrical engineer, but i like tinkering. But the schematics on the d-lev and on this site for building are way to complex for me. But i found a tutorial for a colpitts oscilator. So that was doable. Turns out it wasn’t so great, but it was a start. It lead me to the clapp oscilator, and i build it in a simulator and started to see how it works. Changed a couple of things and build it on a breadboard.

And i didn’t realy expect this, but i got 424Vpp and without grounding 30 to 40 cm range on my pitch antenna (seeing the wave change on the oscilloscoop)

I thought i’d share and maybe ask some questions if i get stuck somewhere.

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"On the main board, I see Mon and Line pins with a jumper. Is it to feed Mon or Line output to the Toslink connector ?" - André

Yes, exactly. This way, the SPDIF MON electrical connection on the expansion port could feed the DAC, and the TOSLINK could be LINE and fed to recording equipment for a cleaner signal (no DAC to ADC conversion).

The only difference between LINE and MON is the presence of pitch preview in the latter, which one generally doesn't want going to the audience.

Let's Design and Build a (mostly) Digital Theremin! (by André)

Very clever design, Eric. Bravo!

On the main board, I see Mon and Line pins with a jumper.
Is it to feed Mon or Line output to the Toslink connector ?

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

Kit #2 - Control Panel

An order of M3x30 nylon screws arrived today so I was finally able to assemble the main control panel.

Above: Guts, with tuner PCB at top, LCD and main PCB at center, encoder PCB at bottom. Note 3D printed shrouds around the tuner LEDs with integrated stand-offs. Also note the cutaway at the bottom of the tuner PCB to make clearance for the LCD pins. The LCD is a 5V unit. Encoders are now combined, though I may make future PCBs so they could be sawed in half.

Above: Guts all purtied-up with the new PCB front panel. The knobs are 3D printed with clear filament.

Above: Rear view of the assembly. You can see the surface-mount LED driver ICs on the tuner PCB and the debounce RCs on the encoder PCB. On the main PCB the 2x8 expansion port has been divided into two 2x5 ports. The left port is for remote control, the right for I/O panel connectivity. Note the new RJ45 jacks for the field coils, one can either use the standard ribbon cable here or CAT5/6 cables to connect the coils.

Above: Side view of the assembly. The multi-level nature of everything was a challenge to address. I ended up employing 3 different length pins for the interconnect. Note how the LCD PCB is exactly the height of the tuner 7-segment display height plus the LCD PCB height (a stroke of good luck). Using short shaft encoders here to make the knobs a bit lower profile.

Going surface mount and getting rid of the tuner and encoder cabling has relieved much of the soldering labor, though there's still a fair number of through-hole connections. Integrating the tuner and going with a PCB front panel has eliminated almost all of the bulk cosmetic 3D printing, which is also nice. These moves should free up more time to spend printing and winding the larger coils. I think one kit per week should be possible once everything is in place. The jigs and fixtures are done, though I need to finalize the AFE, and get some shipping supplies too.

Next up: AFEs & coils.

CHRISTMAS THEREMINOLOGY FESTIVAL ONLINE 2025/26 (by André)

Hey AI! It's time to change your real time clock battery.

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

"Really, are the FPGA I/O not 5V tolerant?" - ILYA

From the Cyclone 4 datasheet, 4.2V is the absolute maximum input voltage. The I/O bank voltage supply max is 3.475V. 5V tolerance disappeared from FPGAs long ago. In this day and age, we're lucky that they can handle 3.3V logic levels!

"Even if they are not, a series resistor of approximately 1 k performs well. I consistently implement such a resistor, even between 5V-to-5V devices, as it offers additional ESD protection."

I do the same, there are 1k resistors (and now ESD diodes) on the FPGA UART leads.

Let's Design and Build a (mostly) Digital Theremin! (by ILYA)

Really, are the FPGA I/O not 5V tolerant?

Even if they are not, a series resistor of approximately 1 k performs well. I consistently implement such a resistor, even between 5V-to-5V devices, as it offers additional ESD protection.

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

Dongle Voltage!

I ordered a few bare dongles from Amazon that have the latest trendy USB C connection and use the CH340N IC:

https://www.amazon.com/dp/B0GL2GBT1G

Testing them on the bench, I noticed the serial connection was operating at 5V - but the FPGA I/O is 3.3V! There's a series resistor on the D-Lev main board, so it's probably OK but not ideal. Looking at the datasheet, the I/O operates at whatever voltage you power the CH340N with, and USB is 5V. I also saw weird random TX events happening here and there, like several times per minute, presumably coming from my Linux system - which is probably not OK.

So I'm sticking with dongles that use the CP2102 IC, which has it's own 3.3V regulator driving the internals and I/O. I've given up on FTDI and Prolific and their attendant turf wars - lots of drama over jellybean parts.

Let's Design and Build a (mostly) Digital Theremin! (by dewster)

Testing Testing...

I've been working on and off for a while now on improving the D-Lev kit. I got a set of PWBs from JLCPCB a week or so ago, and so far everything seems to be OK, though I haven't tested the AFEs yet. I've switched to surface mount components installed by JLCPCB, so the soldering has mostly been reduced to all of the remaining through-hole parts and connectors, of which there are a fair amount. However, the tuner and encoder boards plug directly into the main board now so I don't have to fart around with cabling there. A major goal of the kit rework was to reduce the required manual labor and cosmetic 3D printing, and I believe that's been achieved. The remaining 3D printing is for the coils, which will be significantly larger and more time consuming to wind, though I don't mind this so much because the field coils are the beating heart of the Theremin.

Anyway, the 2x8 IDC expansion port has always been a bit awkward to use. With the new kit, the functionality is separated into to two 2x5 pin IDC connectors. One for the remote control footswitch / push buttons, and the other for SPDIF, MIDI, UART, and power/ground. Making a new test harness for the latter was easy: just a bunch of wires connected to the IDC connector ribbon cable. For the former I designed a test jig:

While designing it I realized I was making a generic project box, so that got spun off into its own thing as a separate file, which was then called in the jig file. It's so nice to be able to 3D print exactly what you need and have it be totally custom! I used 4 push buttons from the junk box, along with a 5mm red LED, some ribbon cable, and a 2x5 IDC connector. Buttons from left to right: Mute (& mute LED), ACAL, preset down, preset up. I plugged it into corresponding expansion port connector on the new kit and everything tested AOK. Of course, I'll be able to use this jig for testing production units too.

Once I receive the remaining parts in the post I'll post some pictures of the new kit.

[EDIT] While using the test jig, I realized the mute LED really kinda corresponds to both the mute and ACAL pushbuttons (since ACAL initiates a temporary mute), which gave the green light to placing the LED between them, which allowed the box to shrink some. I couldn't help myself (anything to postpone real work):

Lost Volts LV-4: Tilting the pitch antenna (by dales)

60 days or so on the LV-4. When Priantz, on YouTube, plays this instrument, he tilts the pitch antenna away from him at what looks like 15 degrees. I believe the tilt is meant to spread out the higher octaves a bit.

He plays this model as well as I’ve heard it played, and he’s also tall and sets the instrument low. All of this is appealing to me.

I’m experimenting with the 15 degree tilt. After a few days of it, I’m trying 20 degrees. With a tilt, it seems like it’s easier to get G4 to G5, G3 to G4, and G2 to G3 within a hand span though not necessarily exact, and with zero beat in front of me. Aspiring Thierry tuning without much experience.

Headphones (by harcel)

I have found out that the hum (which was rather high, around A6) was due to the adapter of the power source, a laptop charger. With another power source (a grounded plug with USB-A connectors) I do need a connection to earth still, so I connected the earth plug on the theremin to the earth pin in the power plug. That removed all noise.
I also replace the small amp by a simple aux cable with volume wheel (short cable, super cheap), which can only lower the volume, but that was the whole point anyway. This works very well, so now I use my headphones without amplification, but with volume control in the wire. This minimizes the gear around the theremin, ideal for on the way!

CHRISTMAS THEREMINOLOGY FESTIVAL ONLINE 2025/26 (by gergesvip9595)

Happy New Year 2026! Thank you for such a warm message. It’s wonderful to see how music festivals bring artists and audiences together and create memories that last beyond the event itself. Wishing all the participants, organizers, and audience members a peaceful, creative, and successful year filled with beautiful music and new inspiration. Here’s to another year of exciting performances and discoveries! sparkling