I built this little nixie pendant for my wife for our anniversary, though it arrived a year late!
A reed switch is used to implement a movement sensor. A sequence of taps and double-taps allow the wearer to control what mode the display is in. It can display various sequences of numbers at various speeds and for various lengths of time.
An accelerometer would have been better than a reed switch, but a movement sensor was a last-minute decision.
Here’s a video of it in action:
The main body contains the power supply, the display board and the reed switch. The power supply has reverse-polarityinput protection and short-circuit protection on the HV. The whole thing is encased in thick transparent heat-shrunk tubing – we don’t want any perspiration getting in there.
There is a LiPo battery behind the wearer’s neck. I would have preferred something incorporated into the body, but the proportions would have looked wrong. The battery has a hard shell to protect it during wear. Wires from the battery to the main unit are woven in to the gold chain that holds the pendant. If the display is permanently on, it lasts for about 10 hours.
The nixie tube itself is a ZM1232 – which has inverted characters, making it well suited to this job.
Here are some construction pictures:
This took a lot longer to develop than I had thought. I originally intended to power it with coin cells. It turns out coin cells just can’t provide the current this needs without suffering severe voltage sag, so I had to go with a larger LiPo. In addition the flyback transformer in the power supply I designed kept overheating. In the end someone suggested a replacement with a higher saturation current. It worked well and was even smaller than the one I had originally chosen. Finally, it took me a long time to figure out how mount it – I’m not very good at such things! Anyway. I’m pleased with the result.