Open Theremin V3 Build: Calibration sounds: yes - other sounds: no

Posted: 5/14/2021 5:12:04 PM

Joined: 5/14/2021


I recently received my Open Theremin kit and got it all soldered up.   When I start it up all the lights work fine and when I calibrate I get the beeps where expected from my speaker.   However, after calibrating several times (all knobs at 12 o'clock, gear on a tripod, ground wire connected to ground, me standing with my arms at my sides) I can't get any other sounds out of it.

I must be doing something wrong here and would welcome any advice or experience any of you might have.

Thanks in advance!


Posted: 5/14/2021 5:56:46 PM

Joined: 5/14/2021

I also opened the Serial Monitor and got the calibration output from the device.   I am not sure how to interpret this as being good or bad....

10:55:31.324 ->
10:55:31.324 -> PITCH CALIBRATION
10:55:31.324 ->
10:55:32.317 -> Arudino Freq: 15985756.00
10:55:32.317 ->
10:55:32.317 -> Pitch Set Frequency: 499745
10:55:34.489 -> Frequency tuning range: 481309 to 518156
10:55:36.697 ->
10:55:36.697 -> DAC value L: 0 Freq L: -17773
10:55:36.697 -> DAC value H: 4095 Freq H: 18513
10:55:38.913 ->
10:55:38.913 -> DAC value L: 4095 Freq L: 18497
10:55:38.913 -> DAC value H: 2006 Freq H: -978
10:55:41.128 ->
10:55:41.128 -> DAC value L: 2006 Freq L: -974
10:55:41.128 -> DAC value H: 2110 Freq H: 262
10:55:43.338 ->
10:55:43.338 -> DAC value L: 2110 Freq L: 263
10:55:43.338 -> DAC value H: 2088 Freq H: 19
10:55:45.531 ->
10:55:45.531 -> DAC value L: 2088 Freq L: 19
10:55:45.531 -> DAC value H: 2087 Freq H: 5
10:55:45.624 ->
10:55:45.624 -> VOLUME CALIBRATION
10:55:45.624 ->
10:55:45.624 -> Volume Set Frequency: 460475
10:55:47.826 -> Frequency tuning range: 0 to 0
10:55:47.826 ->
10:55:47.826 ->

Posted: 5/14/2021 6:03:32 PM

Joined: 5/14/2021

The Frequency Tuning Range: 0 to 0 seems a bit odd to me - but as a noob I have no idea.

Posted: 5/14/2021 9:07:14 PM

From: Occitanie

Joined: 3/4/2012


I looked at the code and at the schematic. 

I am afraid that it is a hardware problem...

The only reason I see for "Frequency Tuning Range: 0 to 0" is that no oscillation is detected on "T0" Pin.
Maybe volume antenna oscillator is not running at all or maybe the signal doesn't make its way to the Atmega ship on the arduino.

You need to track "V0_VOL" signal (see Open Theremin Schematic).
Problem may be on the Arduino or on the schield.

Posted: 5/14/2021 9:10:31 PM

From: Colmar, France

Joined: 12/31/2007

Mr_Dham is right, the volume oscillator doesn‘t work or its signal doesn‘t pass through to the Arduino pin;

@Mr_Dham: Je passe régulièrement les vacances de la Toussaint en Occitanie. Serait-il peut-être possible de se voir cette année?

Posted: 5/14/2021 9:14:50 PM

Joined: 5/14/2021

Thanks Mr_Dham and Thierry - I will track that down!

Posted: 5/14/2021 9:42:10 PM

From: Occitanie

Joined: 3/4/2012

@IamTomzo: let'us know about your success in fixing this issue...

@Thierry: Se voir, oui, c'est une bonne idée. (Voir mon message privé pour plus de précision géographique).

Posted: 5/14/2021 10:56:35 PM

Joined: 5/14/2021

Thanks - I inspected the hardware and the soldering and it is all in good shape.   I have not gotten out the multimeter yet, but have ordered a new Uno that will arrive tomorrow.   If the same thing happens with the new Uno I will have narrowed down the source of the matter.

Posted: 5/16/2021 2:18:14 AM

Joined: 5/14/2021

Well I got a new Uno today (genuine version - not a knock off) and the same symptoms persist.   I took the Open Arduino shield back out to the workshop and reflowed all solder joints - everything is solid.   I presume the volume oscillator is on the Uno, correct?

I did notice some locations marked TP-6 and TP-7 that are inline with where the antennae connect but did not see any instructions on what those are used for.   Could it be that they need to be jumped to the antennae?

I looked at the schematic but other than what I soldered on I am not sure there is much I can do - any thoughts?

Any advice is appreciated.



Posted: 5/16/2021 10:07:33 AM

From: Occitanie

Joined: 3/4/2012

First, to avoid word confusion, let's speak about arduino board one one side and open theremin shield on the other:
  The arduino board is just hosting the Atmega ship and all needed stuff to have it working (PSU, clock, connectors, serial port, USB, ...).
  The volume oscillator is on the open theremin schield.

TP-6 and TP-7 are test points. You normaly don't need to solder anything there. You may use it to put the oscilloscope probe and track the signal.
Even without antenna the oscillator should oscillate. So it's probably not a bad contact between antenna and open theremin Shield.

This lead me to an essential question: do you have access to an oscilloscope ?
If yes you can track the signal: Do you see 460 Khz at TP7 ? (oscillator working ? )
Do you see it on arduino board at "Pin 4" ? (continuity ?)

If you don't have an oscilloscope, you still can track continuity with a multimeter, track power supply at U5 4069 ship, ...
But you won't know if your volume oscillator works correctly.

The arduino being sandwiched with the shield won't help investigations, of course. some "jumper wires" (search "arduino jumper wire") may be usefull.

Continuity: solder joint are one thing, you may also search for broken tracks (less probable but we never know...), ...

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