OpenTheremin v3 for Tesla Coil

[profdc9]

So I built my theremin and while it works, it is not the greatest.  As predicted, the RC-based theremin is a good noisemaker but is hard to control.

So instead, I am going to modify OpenTheremin v3 to directly be an interrupter.  I laid out the board for thru-hole, which I have attached.  A picture of the board is here:



Since there are no thru-hole varactors anymore as far as I can tell, I used four 1N4001 in parallel which roughly has the same capacitance as the varactors used in the OpenTheremin (BB914).

I also got rid of the Arduino and just put the Atmega328 on the board itself, as well as the power supply, so it is self contained, and I added a circuit to output the MIDI.

Dan

[Mads Barnkob]

Did you get any videos done of using the RC theremin on a DRSSTC?

Did you use the MIDI "hack" that someone else already made for the OpenTheremin?

[profdc9]

I haven't got any video yet, I am behind in my work because I have been playing too much but maybe this weekend if the weather cooperates I can get some video.

I added a couple of things to the board.  One is an output for the MIDI using the TX of the AVR (which does double duty as if the ATmega328p is flashed with the Arduino bootloader, you can use a serial port interface to flash the mega as well).  I also added a LM386 to the board so you can get a low power amplified output directly from the board, and you don't need an external amplifier if you just want to use it as a portable Theremin.



The revised project is attached.

Dan

[profdc9]

Hello,

I built an OpenTheremin v3 based on only thru-hole parts.  The PCB is below.



It works, but I had to experiment a bit to find diodes that work as varactors.  Unfortunately, there are no available thru-hole varactors anymore.  I figured out that I could use three 10A10 diodes in parallel in place of the varactor.  I'm sure it wouldn't work for RF, but it seems to do ok for the Open Theremin.  I had to use three 10A10 diodes and then add 50-100 pF of capacitance in parallel with that, and then the autotune works.  I modified the board so it can take large diodes in case these are needed as the varactors.

The board I laid out also includes MIDI output (hooked up to a DIN-5 connector) and a small amplifier (LM386), as well as putting the ATMEGA328P on the board so an Arduino Uno is not required.  There is also a place for a IFE97 fiber optic LED which will be used for generating an interrupter output.  It should be possible to modify the standard OpenTheremin v3 to have an interrupter output, as I'm just going to retask one of the LEDs as the interrupter output (the green one).

Probably the 10A10's are less temperature stable than the BB914 diodes but after 15 minutes or so of being turned on the calibration stabilized.

One question I have about the OpenTheremin is that it seems like the volume is muted by putting one's hand closer to the volume antenna.  Is this the way it is supposed to be?

Anyways the Kicad project is attached.

Dan

[futurist]

One question I have about the OpenTheremin is that it seems like the volume is muted by putting one's hand closer to the volume antenna.  Is this the way it is supposed to be?

Yes, it should work like that

Firmware has debug mode and I think it's still not documented, but it might help you to see if everything is working correctly. If you open the serial window in Arduino IDE and set 115200 baud rate and then start the calibration of your theremin you should get the calibration data.  Calibration range is from 0-4096 and you can check if your oscillators are in the range

Did you test it with your DRSSTC?