Board Revision Notes

Board Rev 1

The first revision of the Plasma Speaker board is a single-layer clone of the Franzoli Electronics Easy-Flyback I based on the schematic posted on his site. We created this board as an initial proof of concept and for testing our demo design and any electronics upgrades.

Board Rev 1.5

We quickly found that Franzoli's Easy-Flyback I design produced a great resonating arc and could produce tones with tailored input from a frequency generator, but struggled with general audio playback and line level audio from small devices. It also used complex filters and feedback that made it difficult to debug. We made the following modifications either dead-bug or on a separate breadboard:

• We replaced the zener diode-based 12V regulation circuit with an off-the shelf 12V regulator LM7812 for cleaner, more reliable output with less heat dissipation
• We completely removed all zero-crossing feedback and filters, directly connecting the audio line in to the input of the LM311 comparator used for zero-cross detection. This simplified the circuit and allowed us to add back in the features needed to make the audio come through, including:
  • Adding a band-pass RC filter to the audio input to remove noise
  • When we found that the comparator still required relatively large potentials of ~100mV or more to trigger (much larger than line level audio), we experimented with amplification of the input before finding that biasing the input to the comparator to 6V allowed for a much more sensitive zero-cross detector capable of playing back relatively clean plain audio files from any device. We accomplished this by using the high-pass portion of our band-pass filter for isolation of the audio input, and setting the reference of the comparator and the resting state of the signal comparator input to 6V with a resistor divider.
  • We traded the resistors in the reference resistor divider for a trimpot that allows for adjustment of arcing sensitivity (arc always on -> various sensitivity to audio input -> always off)
  • We added more capacitors in parallel on the power line to avoid heat issues
  • We re-wired the arcing button to allow for test arcing with the new biased setup

We also ran various tests (see the Tests page) to understand how to continue changing the board for our final design.

Board Rev 2

This is the final 2-layer professionally fabricated board for 2022.