A digital dash is cool and all, but analog gauges have lasting appeal. There’s something about the simplicity of a purely mechanical gauge connected directly to a vehicle’s transmission. Of course that’s not what’s hapenning here. Instead, this build is an analog display for GPS-acquired speed data.
The video below does a good job at explaining the basics of [Grant Stephens]’ build. The display itself is a gutted marine speedometer fitted with the movement from a motorcycle tachometer. The tach was designed to take a 4-volt peak-to-peak square wave input signal, the frequency of which is proportional to engine speed. To display road speed, [Grant] stuffed an ATTiny85 with a GPS module into the gauge and cooked up a script to convert the GPS velocity data into a square wave. There’s obviously some latency, and the gauge doesn’t appear to register low speeds very well, but all in all it seems to match up well to the stock speedo once you convert to metric.
There’s plenty of room for improvement, but we can see other applications where an analog representation of GPS data could be useful. And analog gauges are just plain fun to digitize – like these old meters and gauges used to display web-scraped weather data.