I began this project with the intention of creating a Theremin for my Mom, who has also been fascinated by the instrument but never had one. I have seen a lot of designs ranging from very simple to very complex, but I wanted to make something something… different. I intended to approach this project with a structured mindset in order to test my engineering abilities to follow through on a  design from inception to completion.

The final product – the Theremean!

Concept: I wanted a straightforward design with off-the-shelf components and easily-fabricated sub-assemblies, a controlled BOM with a minimum number of vendors and short lead-times. I settled on making a modified version of the Open.Theremin.Uno, in my own plastic case and using a custom PCB with my own design flare. I designed in all the standard/extra features: volume control, waveform selection, a calibrate button, power LED, calibrate LED, CV output, MIDI output, and an internal speaker tied to a switched headphone/line output. I decided to power the unit with a shielded (so it doesn’t interfere with the antennae) line power plug connected to an internal DC power supply module. I used banana plugs to make the antennae easily removable, and, finally, added the unique feature of a built-in distortion output stage, which inspired the puntastic name of Theremean!

Guts Shot

BOM: The Bill of Materials below shows all of the components that went into the final build (but not any tweaks that were made post-production). I broke the cost-per-unit down into 1/10/100 quantities to show how much it might cost if I had chosen to build these in a larger quantity; I ended up building 3 units at a cost of around $85/ea, knowing that I could build 100 units at a noticeably lower cost of $58/ea. These numbers are just for reference, though, because it does not account for any capital costs (equipment, solder paste mask), labor (I like to value my time at around $0.00/hr for personal projects; I’m doing this for fun, after all), design time, troubleshooting time, extra parts, electricity, lack of sleep, and anything else I can’t remember (due to lack of sleep?).

ManufacturerManufacturer Part NumberVendorVendor Part NumberDescriptionQuantityCost @ 1Cost @ 10Cost @ 100
PolycaseJB-35R*0000Instrument Case 5.00 x 3.80 x 1.50 in1.00$7.54$6.25$4.97
PolycaseSCREW-MBR-100PCB Mounting screws4.00$0.04$0.04$0.04
*OSH ParkTheremean V1Blank PCB - Custom Design1.00$15.59$9.37$9.37
K&S Precision Metals103McMaster-Carr7237K15Antenna Metal2.00$1.01$1.01$1.01
VishayVJ0805G106KXQTW1BCMouser77-VJ0805G106KXQTBCMultilayer Ceramic Capacitors MLCC - SMD/SMT 0805 10uF 10volts X5R 10%2.00$0.10$0.10$0.07
KemetC0805C103K5RACTUMouser80-C0805C103K5RMultilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 10000pF X7R 10%3.00$0.10$0.02$0.01
KemetC0805C473K5RACTUMouser80-C0805C473K5RMultilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 47000pF X7R 10%1.00$0.10$0.03$0.02
KemetC0805C682K5RACTUMouser80-C0805C682K5RMultilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 6800pF X7R 10%1.00$0.10$0.04$0.03
VishayVJ0805A470GXACW1BCMouser77-VJ0805A470GXACBCMultilayer Ceramic Capacitors MLCC - SMD/SMT 0805 47pF 50volts C0G 2%2.00$0.10$0.10$0.03
MurataGRM2165C1H471JA01JMouser81-GRM215C1H471JA01JMultilayer Ceramic Capacitors MLCC - SMD/SMT 0805 470pF 50volts C0G 5%1.00$0.19$0.08$0.05
MurataGRM2165C1H331JA01DMouser81-GRM40C331J50DMultilayer Ceramic Capacitors MLCC - SMD/SMT 0805 330pF 50volts C0G 5%2.00$0.18$0.07$0.04
VishayCRCW08052K20JNEAMouser71-CRCW08052K20JNEAThick Film Resistors - SMD 1/8watt 2.2Kohms 5%1.00$0.10$0.04$0.02
VishayCRCW08051M00JNEAMouser71-CRCW0805J-1M-E3Thick Film Resistors - SMD 1/8watt 1Mohms 5% 200ppm4.00$0.10$0.04$0.02
VishayCRCW0805470RJNEAMouser71-CRCW0805J-470-E3Thick Film Resistors - SMD 1/8watt 470ohms 5% 200ppm2.00$0.10$0.04$0.02
VishayCRCW0805330RJNEAMouser71-CRCW0805J-330-E3Thick Film Resistors - SMD 1/8watt 330ohms 5% 200ppm7.00$0.10$0.04$0.02
Molex15-91-2060Mouser538-15-91-2060Headers & Wire Housings HDR DUAL SMT 6P1.00$0.43$0.32$0.28
Molex22-15-2066Mouser538-22-15-2066Headers & Wire Housings 6P RT ANGL PCB RECEP1.00$0.73$0.55$0.48
Molex22-15-2026Mouser538-22-15-2026Headers & Wire Housings 2.54MM BOARD CONN RA 2 CKT Tin1.00$0.26$0.18$0.15
Schurter3404.2416.11Mouser693-3404.2416.11Surface Mount Fuses UMZ 250 FUSE WITH HOLDER 1A T1.00$1.41$1.41$1.17
EPCOS / TDKB72650M301K72Mouser871-B72650M301K72Varistors 300V 400A 45pF Varistor1.00$1.00$0.76$0.42
Texas InstrumentsRC4558PWMouser595-RC4558PWOperational Amplifiers - Op Amps Dual General-Purpose Op Amp2.00$0.39$0.27$0.12
Lite-OnLTL2R3KGD-EMMouser859-LTL2R3KGD-EMStandard LEDs - Through Hole Thru-Hole Lamp 5mm Grn 571nm 30Deg1.00$0.08$0.08$0.06
Lite-OnLTL2R3KYD-EMMouser859-LTL2R3KYD-EMStandard LEDs - Through Hole Thru-Hole Lamp 5mm Ylw 592nm 30deg1.00$0.08$0.08$0.06
BournsPTL45-10R1-203B2Mouser652-PTL45-10R1-203B2Slide Potentiometers 20Kohms Travel=45mm Center Detent3.00$2.30$1.81$1.60
ApemMHPS2273NMouser642-MHPS2273NPushbutton Switches Momentary key DP1.00$0.83$0.83$0.71
ApemMH12Mouser642-MH12Switch Bezels / Switch Caps TALL SQ BLACK CAP1.00$0.19$0.19$0.18
KyconKCDX-5S-NMouser806-KCDX-5S-NCircular DIN Connectors 5P R/A PCB NON SHLD 10mm CIRC DIN RECPT1.00$1.11$1.11$0.77
Switchcraft35RASMT4BHNTRXMouser502-35RASMT4BHNTRXPhone Connectors SMT 3.5MM PHONE JACK1.00$0.69$0.68$0.65
Kobiconn174-R819B-EXMouser174-R819B-EXTest Plugs & Test Jacks L 1.88" 10A BLACK2.00$1.20$0.99$0.90
Cinch Connectivity Solutions108-0903-001Mouser530-108-0903-1Test Plugs & Test Jacks BANANA JACK BLACK BU-31602-02.00$0.52$0.47$0.41
Heyco1137Mouser836-1137Cable Mounting & Accessories SR 5P3-4 BLACK1.00$0.13$0.13$0.09
3MSJ-5003 (BLACK)Mouser517-SJ-5003BKMounting Hardware SMALL HEMISPHERE BLK 56 PER PAD4.00$0.11$0.06$0.06
Volex17740 10 B1Mouser686-17740AC Power Cords 18AWG PLUG-SVTS 6FT 7IN (2.0m) BLACK1.00$5.93$5.93$5.19
AVXTPSD337M006R0070Mouser581-TPSD337M006R0070Tantalum Capacitors - Solid SMD 6.3V 330uF 20% Tol. 70 ESR2.00$1.18$1.18$0.97
VishayCRCW080510K0JNEAMouser71-CRCW0805J-10K-E3Thick Film Resistors - SMD 1/8watt 10Kohms 5% 200ppm8.00$0.10$0.04$0.02
VishayCRCW0805100KJNEAMouser71-CRCW0805J-100K-E3Thick Film Resistors - SMD 1/8watt 100Kohms 200ppm2.00$0.10$0.04$0.02
VishayCRCW08054M70JNEAMouser71-CRCW08054M70JNEAThick Film Resistors - SMD 1/8watt 4.7Mohms 5%4.00$0.10$0.04$0.02
ToshibaTC7WHU04FUTE12LFMouser757-TC7WHU04FUTE12LFInverters x34 INVERTER(UNBUFF)3.00$0.43$0.33$0.20
KemetC0805C104K5RACTUMouser80-C0805C104K5RMultilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 0.1uF X7R 10%14.00$0.03$0.02$0.01
MurataGRM2165C1H131JA01DMouser81-GRM215C1H131JA01DMultilayer Ceramic Capacitors MLCC - SMD/SMT 0805 130pF 50volts C0G 5%2.00$0.11$0.05$0.03
VishayVJ0805A180GXACW1BCMouser77-VJ0805A180GXACBCMultilayer Ceramic Capacitors MLCC - SMD/SMT 0805 18pF 50volts C0G 2%6.00$0.10$0.04$0.02
RECOMRAC02-05SCMouser919-RAC02-05SCAC/DC Power Modules CONV AC/DC 2W 80-264VIN 05VOUT1.00$12.78$12.60$11.11
AtmelATMEGA328P-AUMouser556-ATMEGA328P-AU8-bit Microcontrollers - MCU 32KB In-system Flash 20MHz 1.8V-5.5V1.00$3.43$3.02$2.27
MurataTZB4P300AA10R00Mouser81-TZB4P300AA10R00Trimmer / Variable Capacitors 4mm 30pF2.00$0.91$0.65$0.57
ABRACONABMM2-16.000MHZ-E2-TMouser815-ABMM2-16-E2TCrystals +/-20PPM 16MHz1.00$1.16$1.02$0.65
ABRACONABMM2-8.000MHZ-E2-TMouser815-ABMM2-8-E2TCrystals 8MHz1.00$0.93$0.82$0.65
ABRACONABMM2-7.3728MHz-E2-TMouser815-ABMM2-7.3-E2-TCrystals 7.3728MHz, 18pF 20ppm1.00$0.93$0.82$0.68
MicrochipMCP4921-E/SNMouser579-MCP4921-E/SNDigital to Analog Converters - DAC Sgl 12-bit SPI int1.00$2.08$1.97$1.49
ON SemiconductorMC74AC74DR2GMouser863-MC74AC74DR2GFlip Flops 2-6V CMOS Dual D-Type Pos. Edge1.00$0.45$0.33$0.21
Texas InstrumentsLM358DMouser595-LM358DOperational Amplifiers - Op Amps Dual Linear1.00$0.44$0.30$0.14
Texas InstrumentsCD4060BM96Mouser595-CD4060BM96Counter ICs CMOS 14-St Ripple- Carry Binary2.00$0.44$0.34$0.18
TDKNL453232T-102J-PFMouser810-NL453232T-102JPFFixed Inductors 1K UH 5%2.00$0.49$0.35$0.23

Case: The case was a standard plastic case, the JB-35R*0000 from Polycase, which I hand-machined with various holes using step-bits and blades/files. The unit in the pictures here was my first unit, with some extra “oops” holes and access to the programming header. For a larger quantity of builds, I would have paid the ~$100 setup fee to have Polycase machine these for me and add fancy graphic overlays. Instead, I created the design in Inkscape as an overlay of the manufacturer’s dimensioned drawing, and printed it out on large white label stock. After attaching it to the case, I used the black areas as a cutting template.

Front Panel Layout

PCB: While I based the design on the Open.Theremin.Uno, I made some PCB BOM changes to optimize the components and layout. I also used this as a moment to try my hand at making a board with 0805 passives; while I have experience designing as small as 0402 passives into PCBAs for work, we have those assembled professionally with pick-and-place, and I have never tried something smaller than 1206 for hand-placed SMT work. It turned out fine, and I could have made the layout much tighter if I had wanted to; in fact, in hindsight it looks like I subconsciously left as much spacing as I would have for 1206. I had the PCBs made by the always-awesome OSH Park, and I had a solder paste stencil made by OSH Stencils. Theremean KiCad Archive for download, if you’re into that kind of thing.

KiCad Schematic
KiCad Rendering – Front
KiCad Rendering – Back

Other Notes:The antennae were made from 5/32″ OD (0.128″ ID) aluminum tubes, hand-shaped and soldered to banana plugs, with some adhesive heatshrink for protection and looks. The mating blue banana jacks were used because I had them on hand already, and I used slider potentiometers with LEDs just to give it some color. I used the original Open.Theremin.Uno Arduino code without any memorable issues; I may have added a few tweaks, I can’t remember.

The distortion effect gave me some trouble; I based it on some guitar effects designs I found online, but after the build I discovered some items that needed to be changed, which are noted on the schematic.

I had some trouble with the original tank capacitor values (probably since they were selected for a different PCB design with its own internal capacitances), so I had to solder in some other values in parallel to give me the capacitance I needed to calibrate the unit correctly. An improvement in the future would be to add a digital capacitor IC (a switched capacitor bank, essentially) to allow the calibration to be automatic, because it was rather finicky.

I am happy with the final product. I kept the first one, gave one to my Mom, and gave one to my friend Sean.

UPDATE: Since the completion of this project, an Open.Theremin.V3 has been released with some newer features; most importantly, the automatic calibration that I wanted to include. But they did it with a tuned diode, instead of a switched capacitor bank (digital capacitor) like I proposed.

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