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.
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!
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?).
|Manufacturer||Manufacturer Part Number||Vendor||Vendor Part Number||Description||Quantity||Cost @ 1||Cost @ 10||Cost @ 100|
|Polycase||JB-35R*0000||Instrument Case 5.00 x 3.80 x 1.50 in||1.00||$7.54||$6.25||$4.97|
|Polycase||SCREW-MBR-100||PCB Mounting screws||4.00||$0.04||$0.04||$0.04|
|*||OSH Park||Theremean V1||Blank PCB - Custom Design||1.00||$15.59||$9.37||$9.37|
|K&S Precision Metals||103||McMaster-Carr||7237K15||Antenna Metal||2.00||$1.01||$1.01||$1.01|
|Vishay||VJ0805G106KXQTW1BC||Mouser||77-VJ0805G106KXQTBC||Multilayer Ceramic Capacitors MLCC - SMD/SMT 0805 10uF 10volts X5R 10%||2.00||$0.10||$0.10||$0.07|
|Kemet||C0805C103K5RACTU||Mouser||80-C0805C103K5R||Multilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 10000pF X7R 10%||3.00||$0.10||$0.02||$0.01|
|Kemet||C0805C473K5RACTU||Mouser||80-C0805C473K5R||Multilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 47000pF X7R 10%||1.00||$0.10||$0.03||$0.02|
|Kemet||C0805C682K5RACTU||Mouser||80-C0805C682K5R||Multilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 6800pF X7R 10%||1.00||$0.10||$0.04||$0.03|
|Vishay||VJ0805A470GXACW1BC||Mouser||77-VJ0805A470GXACBC||Multilayer Ceramic Capacitors MLCC - SMD/SMT 0805 47pF 50volts C0G 2%||2.00||$0.10||$0.10||$0.03|
|Murata||GRM2165C1H471JA01J||Mouser||81-GRM215C1H471JA01J||Multilayer Ceramic Capacitors MLCC - SMD/SMT 0805 470pF 50volts C0G 5%||1.00||$0.19||$0.08||$0.05|
|Murata||GRM2165C1H331JA01D||Mouser||81-GRM40C331J50D||Multilayer Ceramic Capacitors MLCC - SMD/SMT 0805 330pF 50volts C0G 5%||2.00||$0.18||$0.07||$0.04|
|Vishay||CRCW08052K20JNEA||Mouser||71-CRCW08052K20JNEA||Thick Film Resistors - SMD 1/8watt 2.2Kohms 5%||1.00||$0.10||$0.04||$0.02|
|Vishay||CRCW08051M00JNEA||Mouser||71-CRCW0805J-1M-E3||Thick Film Resistors - SMD 1/8watt 1Mohms 5% 200ppm||4.00||$0.10||$0.04||$0.02|
|Vishay||CRCW0805470RJNEA||Mouser||71-CRCW0805J-470-E3||Thick Film Resistors - SMD 1/8watt 470ohms 5% 200ppm||2.00||$0.10||$0.04||$0.02|
|Vishay||CRCW0805330RJNEA||Mouser||71-CRCW0805J-330-E3||Thick Film Resistors - SMD 1/8watt 330ohms 5% 200ppm||7.00||$0.10||$0.04||$0.02|
|Molex||15-91-2060||Mouser||538-15-91-2060||Headers & Wire Housings HDR DUAL SMT 6P||1.00||$0.43||$0.32||$0.28|
|Molex||22-15-2066||Mouser||538-22-15-2066||Headers & Wire Housings 6P RT ANGL PCB RECEP||1.00||$0.73||$0.55||$0.48|
|Molex||22-15-2026||Mouser||538-22-15-2026||Headers & Wire Housings 2.54MM BOARD CONN RA 2 CKT Tin||1.00||$0.26||$0.18||$0.15|
|Schurter||3404.2416.11||Mouser||693-3404.2416.11||Surface Mount Fuses UMZ 250 FUSE WITH HOLDER 1A T||1.00||$1.41||$1.41||$1.17|
|EPCOS / TDK||B72650M301K72||Mouser||871-B72650M301K72||Varistors 300V 400A 45pF Varistor||1.00||$1.00||$0.76||$0.42|
|Texas Instruments||RC4558PW||Mouser||595-RC4558PW||Operational Amplifiers - Op Amps Dual General-Purpose Op Amp||2.00||$0.39||$0.27||$0.12|
|Lite-On||LTL2R3KGD-EM||Mouser||859-LTL2R3KGD-EM||Standard LEDs - Through Hole Thru-Hole Lamp 5mm Grn 571nm 30Deg||1.00||$0.08||$0.08||$0.06|
|Lite-On||LTL2R3KYD-EM||Mouser||859-LTL2R3KYD-EM||Standard LEDs - Through Hole Thru-Hole Lamp 5mm Ylw 592nm 30deg||1.00||$0.08||$0.08||$0.06|
|Bourns||PTL45-10R1-203B2||Mouser||652-PTL45-10R1-203B2||Slide Potentiometers 20Kohms Travel=45mm Center Detent||3.00||$2.30||$1.81||$1.60|
|Apem||MHPS2273N||Mouser||642-MHPS2273N||Pushbutton Switches Momentary key DP||1.00||$0.83||$0.83||$0.71|
|Apem||MH12||Mouser||642-MH12||Switch Bezels / Switch Caps TALL SQ BLACK CAP||1.00||$0.19||$0.19||$0.18|
|Kycon||KCDX-5S-N||Mouser||806-KCDX-5S-N||Circular DIN Connectors 5P R/A PCB NON SHLD 10mm CIRC DIN RECPT||1.00||$1.11||$1.11||$0.77|
|Switchcraft||35RASMT4BHNTRX||Mouser||502-35RASMT4BHNTRX||Phone Connectors SMT 3.5MM PHONE JACK||1.00||$0.69||$0.68||$0.65|
|Kobiconn||174-R819B-EX||Mouser||174-R819B-EX||Test Plugs & Test Jacks L 1.88" 10A BLACK||2.00||$1.20||$0.99||$0.90|
|Cinch Connectivity Solutions||108-0903-001||Mouser||530-108-0903-1||Test Plugs & Test Jacks BANANA JACK BLACK BU-31602-0||2.00||$0.52||$0.47||$0.41|
|Heyco||1137||Mouser||836-1137||Cable Mounting & Accessories SR 5P3-4 BLACK||1.00||$0.13||$0.13||$0.09|
|3M||SJ-5003 (BLACK)||Mouser||517-SJ-5003BK||Mounting Hardware SMALL HEMISPHERE BLK 56 PER PAD||4.00||$0.11||$0.06||$0.06|
|Volex||17740 10 B1||Mouser||686-17740||AC Power Cords 18AWG PLUG-SVTS 6FT 7IN (2.0m) BLACK||1.00||$5.93||$5.93||$5.19|
|AVX||TPSD337M006R0070||Mouser||581-TPSD337M006R0070||Tantalum Capacitors - Solid SMD 6.3V 330uF 20% Tol. 70 ESR||2.00||$1.18||$1.18||$0.97|
|Vishay||CRCW080510K0JNEA||Mouser||71-CRCW0805J-10K-E3||Thick Film Resistors - SMD 1/8watt 10Kohms 5% 200ppm||8.00||$0.10||$0.04||$0.02|
|Vishay||CRCW0805100KJNEA||Mouser||71-CRCW0805J-100K-E3||Thick Film Resistors - SMD 1/8watt 100Kohms 200ppm||2.00||$0.10||$0.04||$0.02|
|Vishay||CRCW08054M70JNEA||Mouser||71-CRCW08054M70JNEA||Thick Film Resistors - SMD 1/8watt 4.7Mohms 5%||4.00||$0.10||$0.04||$0.02|
|Toshiba||TC7WHU04FUTE12LF||Mouser||757-TC7WHU04FUTE12LF||Inverters x34 INVERTER(UNBUFF)||3.00||$0.43||$0.33||$0.20|
|Kemet||C0805C104K5RACTU||Mouser||80-C0805C104K5R||Multilayer Ceramic Capacitors MLCC - SMD/SMT 50volts 0.1uF X7R 10%||14.00||$0.03||$0.02||$0.01|
|Murata||GRM2165C1H131JA01D||Mouser||81-GRM215C1H131JA01D||Multilayer Ceramic Capacitors MLCC - SMD/SMT 0805 130pF 50volts C0G 5%||2.00||$0.11||$0.05||$0.03|
|Vishay||VJ0805A180GXACW1BC||Mouser||77-VJ0805A180GXACBC||Multilayer Ceramic Capacitors MLCC - SMD/SMT 0805 18pF 50volts C0G 2%||6.00||$0.10||$0.04||$0.02|
|RECOM||RAC02-05SC||Mouser||919-RAC02-05SC||AC/DC Power Modules CONV AC/DC 2W 80-264VIN 05VOUT||1.00||$12.78||$12.60||$11.11|
|Atmel||ATMEGA328P-AU||Mouser||556-ATMEGA328P-AU||8-bit Microcontrollers - MCU 32KB In-system Flash 20MHz 1.8V-5.5V||1.00||$3.43||$3.02||$2.27|
|Murata||TZB4P300AA10R00||Mouser||81-TZB4P300AA10R00||Trimmer / Variable Capacitors 4mm 30pF||2.00||$0.91||$0.65||$0.57|
|ABRACON||ABMM2-16.000MHZ-E2-T||Mouser||815-ABMM2-16-E2T||Crystals +/-20PPM 16MHz||1.00||$1.16||$1.02||$0.65|
|ABRACON||ABMM2-7.3728MHz-E2-T||Mouser||815-ABMM2-7.3-E2-T||Crystals 7.3728MHz, 18pF 20ppm||1.00||$0.93||$0.82||$0.68|
|Microchip||MCP4921-E/SN||Mouser||579-MCP4921-E/SN||Digital to Analog Converters - DAC Sgl 12-bit SPI int||1.00||$2.08||$1.97||$1.49|
|ON Semiconductor||MC74AC74DR2G||Mouser||863-MC74AC74DR2G||Flip Flops 2-6V CMOS Dual D-Type Pos. Edge||1.00||$0.45||$0.33||$0.21|
|Texas Instruments||LM358D||Mouser||595-LM358D||Operational Amplifiers - Op Amps Dual Linear||1.00||$0.44||$0.30||$0.14|
|Texas Instruments||CD4060BM96||Mouser||595-CD4060BM96||Counter ICs CMOS 14-St Ripple- Carry Binary||2.00||$0.44||$0.34||$0.18|
|TDK||NL453232T-102J-PF||Mouser||810-NL453232T-102JPF||Fixed 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.
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.
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.