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I knew that a small MCU could be run at 3.3V and would drive 25mA from an IO pin, so I decided to see what the tube looked like at 3.3V. Using this information, I had started developing a plan in my head. The Tube Store website has some detailed information on these tubes. Fortunately, I was able to find a datasheet which suggested a filament voltage of up to 4.5V. Since they are incandescent tubes, I figured they’d need a reasonable amount of current to illuminate the segments, but I wasn’t sure at which voltage. The first thing to do was to learn how I would need to drive the tubes. In contrast, numitron tubes use incandescent filaments set out in a 7-segment style arrangement to create numbers. When the voltage is applied, the electric field causes a glow around the negative cathode terminal (shaped like a number). People are more commonly familiar with the nixie tubes (or nixies) which operate at high voltages (typically ~180V DC) with each numerical digit created from a piece of metal inside a glass envelope filled with neon gas. However, the principles of operation are very different. These numitron tubes are often confused with nixie tubes, both with an orange glow.