Ice Tube Clock

The dark spot is normal. Google for 'getter material'.

Getter material evaporated and deposited on the glass. In physics sometimes a so called "titanium sublimation pump (TSP)" is used for ultra high vacuum systems. Titanium has a high "sticking coefficient" and gas just sticks to it. There's also ion getter pumps being used for just holding the pressure.

The filament wires. They're heated up by current and some electrons are 'cooked out'.

A Filament wire again.

A single digit.

Interference fringes of a thin film. I guess some of the getter material (e.g. Barium) deposited there.

x: 5µs/div -- y: 10mV/div

I had to turn on 256x averaging to get the noise down.

x: 100ns/div -- y: 10mV/div

55.2V DC coming from the open loop boost converter. I still wonder how this can provide a stable voltage without any load attached. Theoretically the inductor should charge the capacitor more and more if it is constantly switched. Adafruit recommends to wait a few minutes after testing the step-up converter before going on with the build process. This can be sped up by bleeding the capacitor with your finger across its pins _after unplugging_ the power supply. Skin surface resistance is low enough to make that work. This shouldn't be considered "best practices", but here it is safe enough. Using a 10k resistor to 'short' the capacitor works as well. Don't do this if you're poking around inside something with real high voltages (e.g. old TV sets with several kV).