Dekatron Night Light

This was a fun and relatively fast project inspired by the purchase of a Mullard Z504S dekatron tube.  The Z504S is a compact tube and quite short for a dekatron - less than 1.5" high.  I decided to try to fit one into a "wall wart" power supply case so that it could plug directly into a 120v outlet.

Of course there is more than just a tube in here.  Because dekatrons need ~450v DC and pulse signals to drive them I built a spinner circuit based on a popular online schematic.  This fits on a small piece of perfboard and consists of a few diodes, capacitors, and resistors.  The on/off switch was an obvious necessity.

Because the Z504S is a bi-directional counter I added a slide switch that swaps the two guide pin connections allowing the spinner to run clockwise or counter-clockwise.  It is a nice feature and very simple to add to the circuit with a DPDT switch.

As you can see in the photos there is a good bit of the tube sticking out of the case.  This is intentional and required some spacers below the tube socket to achieve the right
height.  I noticed that although these tubes were meant to be end-viewed, the glow from the cathodes was kind of interesting from the side too.  So the tube protrudes a bit but I think it is a good trade off. 

Here is a short video clip of the night light in action.  The shutter speed of my camera makes it look like one half is lighting, then the other.  Actually the spinning action is quite smooth and fast.

The entire project draws very little power and generates no perceptible heat (these are "cold cathode" tubes after all).  It is not bright enough to see by, but makes a nice night light in the sense that it is a comforting, soothing light that can almost hypnotize one to sleep.