Nixie tubes are interesting pieces of equipment. They certainly looked futuristic when they were first introduced in the 1950s. This kind of “retro-futuristic” look where a glowing numerical display is contained behind a glass tube has obvious appeal to electronics hackers.
In St. Francis, Minnesota resident John Lee’s case, he’s “always wanted to do something with nixie tubes and [he] also wanted to find a minimalist/vintage speedometer solution for the cafe racer project [he’s] been working on for the past couple months.” As this motorcycle was built in 1971, the time period makes perfect sense.
He originally planned to make a three-digit display, but with an engine size of only 175ccs, he doesn’t plan on ever exceeding 99mph. This worked out quite nicely, as he “could mount the tubes in the 2 holes in the triple tree that originally held the handlebar risers.” These holes had to be cut a little larger, but Lee doesn’t anticipate this causing any structural issues.
Speed is measured by four small magnets and a Hall effect sensor, similar to how a road bike’s speedometer works. An up/down counter is used to register the magnets passing, while an Arduino Pro Mini reads this and outputs the proper signal to display the correct number via binary coded decimal (BCD) decoders. Lee plans to do a full tutorial on this build after he designs a proper compact printed circuit board (PCB) for it.
Lee had a lot of the parts for this build already available, but anticipates that building something like this (minus the bike) would cost around $50. Time for him to complete the build was reported at around 10 hours, which is quite impressive given the circuitry involved.
Check out the videos below to see it in action. He explains things in the first video, and a slow test of the speedometer follows in the second. Lee is currently working on getting the bike running smoothly. So, hopefully we’ll get to see those numbers go higher in the future!