Weird sounds of OpenTheremin UNO

Posted: 2/11/2020 2:17:06 PM

Joined: 2/11/2020


 Long ago, I heard about such a musical instrument as theremin. Then I liked it with its sound, however, I did not have the opportunity to get it myself, and forgot about it for a while. And now, less than a week ago I found OpenThereminV3 and found out that it can be done independently. At that moment, I firmly decided that I wanted him, and immediately began to study the topic. 
Realizing that I could not make the third version, the first version of the device attracted my attention. I found a schematic  and pcb on github
., I also found a firmware. Since I did not have enough waiting time, I decided to make a pcb by myself. Then I purchased components from the list from the same link (or their closest analogues), and started working. Yes, before soldering the components, I checked all the tracks and contacts, everything is ok with them. However, when i turned it on, I heard that it was making very weird sound, even when my hands are far away from him. That sound changes tone of you touch an antenna. The only thing I solved was make the volume antenna work (i`ve changed both tuning capacitors), however, the pitch antenna still refuses to work.
What could be the reason?
"I hope this time the page layout will be normal."

Here is which components i`ve replaced
74HC4060D => SN74HC4060D
CD4069UBNSR => CD4069UBM
MC74AC74DR2G => SN74AC74D

Posted: 2/11/2020 2:34:50 PM

From: Northern NJ, USA

Joined: 2/17/2012

Hello smarragd,

Do you have an oscilloscope?  You really need one for this kind of work, otherwise you're reduced to doing go / no-go testing like this, and shooting in the dark.

The creator of the Open.Theremin seems pretty friendly, you might ask him for help.

Posted: 2/11/2020 8:26:18 PM

Joined: 2/11/2020

Hello smarragd,Do you have an oscilloscope? 

For now - I dont have it. If its such important, i can get one. When I get one, what should i try to find? I have no idea where this noise can come from

Posted: 2/11/2020 9:30:29 PM

From: Northern NJ, USA

Joined: 2/17/2012

"For now - I dont have it. If its such important, i can get one. When I get one, what should i try to find?"  - smarragd

Check that the pitch and volume fixed oscillators are working, and that their dividers are working correctly.

Check that the pitch and volume variable oscillators are working, and that their frequencies can be adjusted via the variable capactiors to be in the proper range.

Check that the pitch and volume flip flop mixers are working, and that they are providing good signals to the arduino.

Check the digital signals going into the DAC, and the analog output.

With digital stuff, one wrong connection and everything can go to hell.

Posted: 2/12/2020 7:17:31 AM

From: Colmar, France

Joined: 12/31/2007

The Open.Theremin UNO is extremely sensitive to grounding. Make sure that it’s well grounded.
It’s also extremely sensitive to clock jitter when using a cheap Arduino clone where the XTAL has been replaced by a ceramic resonator.
It’s somewhat sensitive to “dirt” on the supply line. Try with a well regulated (linear) PS.

Posted: 2/12/2020 4:57:32 PM

From: Porto, Portugal

Joined: 3/16/2017

smarragd: IC replacements are ok.
Open.Theremin schematic is complicated. I'm afraid, it would be hard to get it working w/o scope.
But you can make logic analyzer and frequency meter if you have some fast MCU dev board.

Easy way might be just to order assembled OpenThereminV3 shield and antennas from author, although its price, 89 euros, looks high enough.

BTW, I'm currenlty working on open source / open hardware project which may be considered as modern version of Open.Theremin
As Open.Theremin, it uses MCU as a core. But Teensy4.0 is 1000 times more powerful (800MHz, avg 1.5 instructions per cycle ARM core with floating point support, 1MB of RAM) than ancient UNO, and its hardware is capable to implement simple but precise capacitive sensors.
Instead of oscillators and heterodynes, DAC + varistor controls, it's based on measuring of phase shift of reference frequency signal passed through LC tank.
Only two buffer ICs per antenna, connected directly to MCU board pins instead of complicated cirquits.
Project is on early stage: working on testing of sensor on real hardware. I've got my sensor PCBs ordered from chinese PCB manufacturer, and most of parts. Waiting for delivery of a few missing parts I've ordered and 0.125mm copper wire for inductor.
If you like to experiment with DIY electronics and MCU programming, feel free to join
Once phase shift sensor approach got proof of work, it would be easy (and interesting) to implement the rest.
Teensy4.0 is powerful enough to implement virtually any synthesizer. LCD touch will provide convenient visual pitch preview. Audio board, by default, provides CD quality 44100x2x16bit playback.

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