Last year , I took interest @psicman display project more importantly the HID(Human Interface Device) aspect as camera tracking solutions are hardware intensive I elected to to develop an analog alternative. The when the thought of a theremin based mouse came me , as well as it’s potentional as a tool for individuals with hand mobility issues. I optimistically said and I quote “…I should have a proof of concept done by end of week”
…three months 23 days later …
I have managed to get a circuit which kind of works.
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it took me 2 years to get my project to where it is now so it’s not that slow…
Milestone the oscillators. The working principle of a theremin has to oscillators running within the same frequency range and the user’s hand acting as an external capacitor altering the resonant frequency.The change in frequency caused by the user’s hand movement will be detected as an audio signal as the sister oscillator cancels out like frequencies. . The first schematic below is a single transistor Colpitts oscillator taken from this YouTube - https://www.youtube.com/watch?v=78qzLAvGHl0. I just have identical circuits running in tandem.
and their oscillation.
.
The initial circuit was assembled on a thin piece of proto-board which worked fine.
Until I assembled the second circuit then it went haywire . Turns RF oscillator tend to interfere with each other a close proximity.
Next on the agenda is to:
Mix the signals and extracting the audio component left as a result of my hand movement.In my previous attempts I tried using an op-amp(which apparently are terrible at RF frequencies) . I looked into transistor based mixers however the final iteration of this project will stray not have anything to do with RF so it is not worth the heartache.So a diode as mixer will suffice.
My electronics theory is rusty as heck but is this a job for a phase locked loop? The hand changes the frequency of the oscillator so the sensor part is essentially an FM demodulator, right?
Just wondering if there are off the shelf ICs for FM radio type stuff that could be used for this application.
You could make a theremin with a 555 timer the CMOS variant (lower leakage ) the idea is the threshold capacitor will be replaced with a the antenna. This approached was used in C64 theremin https://www.google.com/url?sa=t&source=video&cd=&ved=2ahUKEwi67vHV9rCLAxXQAzQIHb1CKSoQo7QBegQIDRAE&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DWZKklJG-UaY&usg=AOvVaw0zbwDldn4uVp7SwqYrJs64&opi=89978449.
In terms of off the shelf ICs that’s the only approach I am aware of .
I meant for the detector part that converts the analog signal into digital mouse commands.
Although with microcontrollers these days I imagine a DSP running a FFT might be simpler to implement.
I was thinking the esp32 running bike mouse and a basic function the maps Analog signal to mouse coordinates.
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