Tiny Time-of-Flight Plasma Theremin: the Plasmino

Time to think about Impedance matching!

The shockwave produced by the plasma has a lot of force, but over a small small volume. So it probably is not very well acoustically matched to the surrounding air.  An Acoustic horn is a geometrical structure that helps match the impedance to get as much power into the surrounding air:

The plan is to use a bilaterally symmetrical horn to acoustically match the approximately 1-dimensional plasma speaker to the surrounding air:

 This will be printed in PLA, and contain the Arduino Nano, the VL53L0X sensors, and in the middle, the plsma spark-gap.

As promised, here are some demo's:

OK, Go the VL53LOX sensors working. Will post a video tomorrow.

Basically it works like this

We generate 2 sets of square wave pulses, at ultrasonic frequencies

1)  ⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍
2) _⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍⎍

They are out of phase, and the generated plasma expands the air.

If we turn this on and off at audio frequencies, we cause vibrations in the air, as the plasma expands and contracts.

1)  ⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍
2) _⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍____⎍⎍⎍⎍⎍⎍

We can also modulate the volume by changing the duty-cycle, but keeping the frequency the same:

Louder
1)  ⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____
2) _⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____⎍⎍⎍⎍⎍_____

Quiter

1)  ⎍⎍⎍_______⎍⎍⎍_______⎍⎍⎍_______⎍⎍⎍_______⎍⎍⎍_______
2) _⎍⎍⎍_______⎍⎍⎍_______⎍⎍⎍_______⎍⎍⎍_______⎍⎍⎍______

Pretty simple!

OK, plasma speakers are GO!

Here's the rough schematic for the plasma lighter:

Two opposite PWM signals are fed into s1 and s2 to pulse current though the coils in the high voltage transformer, at ultrasonic frequencies.

I plan to pulse the PWM signals to generate audible tones. More to come soon.

OK, I've stripped down a dual-arc lighter, and reverse engineered the circuit.

Seems to be just 2 mosfets, a few resistors and the pulse generator/LiPo charger that I won't be needing at this stage.

I've started coding a Arduino Nano clone to generate the note, as done previously here:

http://ultrakeet.com.au/write-ups/modulated-arc-lighter

After that, I'll add in VL53LOX TOF sensor support.