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Step 2Power supply (Boost Converter)
Nixie tubes are powered by a high voltage source (about 180 volts). To get this voltage we use a boost converter. An induction coil is abused pump-like to fashion 180 volts from 5 volts. Cool. Everything I know about boost converters can be found in this instructable [http://www.instructables.com/id/EHF3DSER24EP286HG8/].
The actual power supply design is taken from my attempt at a nixie watch, see it here [http://www.instructables.com/id/EMR0RL7C56EP2877RA/]. The main difference between this supply and the reference supply in the boost converter instructable is a reduction of components. There are no indicator lights, no large expensive filter caps, and only one input cap. Since the ornament is a single tube, dropping a few capacitors has no functional impact.
I also dropped supply voltage calibration. In the reference design the PIC measures the input voltage and calculates the ideal charge and discharge time for the inductor given the inductor size (mA) and value (uH). I just calculated the charge/fall time for the coil based on a 6 volt supply and hard-coded these values (worst case scenario with 4 AA batteries, though I use NiMH). If the supply is lower (as with my NiMH) the coil is not being used to its full potential, but it doesn't matter because we only need a few mA of HV for a single tube. Sweet. And we saved 2 more resistors. More than 6V will probably cause over heating in the inductor/FET.
Note: There is a 5.1v zener with 1 ohm resistor to protect the uC if the supply is > 5 volts, but this isn't a problem with NiMH or a wall-wort
The actual power supply design is taken from my attempt at a nixie watch, see it here [http://www.instructables.com/id/EMR0RL7C56EP2877RA/]. The main difference between this supply and the reference supply in the boost converter instructable is a reduction of components. There are no indicator lights, no large expensive filter caps, and only one input cap. Since the ornament is a single tube, dropping a few capacitors has no functional impact.
I also dropped supply voltage calibration. In the reference design the PIC measures the input voltage and calculates the ideal charge and discharge time for the inductor given the inductor size (mA) and value (uH). I just calculated the charge/fall time for the coil based on a 6 volt supply and hard-coded these values (worst case scenario with 4 AA batteries, though I use NiMH). If the supply is lower (as with my NiMH) the coil is not being used to its full potential, but it doesn't matter because we only need a few mA of HV for a single tube. Sweet. And we saved 2 more resistors. More than 6V will probably cause over heating in the inductor/FET.
Note: There is a 5.1v zener with 1 ohm resistor to protect the uC if the supply is > 5 volts, but this isn't a problem with NiMH or a wall-wort
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