Luke Miller have purchased a vintage pickup truck and decided to add some electronics in to it. So he came up with idea of adding a Nixie tube based speedometer. Instead of using trucks cables and other sensors he used a GPS receiver for measuring speed. This way device came out to be universal that may be used in any car if you wish.
Nixie display tubes require pretty high voltage to be driven. For this there is a DC voltage converter used. Tube segments are driven using K155ID1 drivers that are specially designed for this purpose. To access GPS signals, there is a PmodGPS receiver used. All that fun is controlled by Basys2 Spartan-3E FPGA board. GPS module sends data stream via USART that can be captured and decoded. The only one thing is needed is speed data. Via trial and error method the data was decoded (seems that documentation of GPS receiver is scarce). A simple look-up table helped to convert kph in to mph. Since truck doesn’t exceed the 99mph there are two Nixie tubes used. If you are interested in this design you can access all documents at theFPGAexpert.com page.