Analog Guts Display GPS Velocity In This Hybrid Speedometer

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.


21 thoughts on “Analog Guts Display GPS Velocity In This Hybrid Speedometer

  1. Pretty nice! The latency seems worse than I would expect at slower speeds, but over all well done. Should add the ability to act as a voltmeter as well if it’s plugged in to the car’s power port (aka cigarette lighter plug for us old folks).

    1. The top speedo has since gone back into the boat. The boat’s original method used the water pressure to get speed, but the water that our boat goes in is simply too dirty and the sensor kept on getting blocked up.

  2. Funny how technology evolves… it seems to be easier for a hobbyist to build a system that relies on multiple satellites hundreds of miles high up in the sky (actually space) then it would be to connect to the can-bus of the car just a few feet of cable length away. This is an ode to the technological achievement of mankind.

    Then again, since the invention of television (1926, that’s 90 years from now) which was technologically perfected 20 years ago to a system that had only 2 perhaps 3 world wide accepted standards, we now have to decide which kind of screen size we want SD, HD, 4K, curved, flat, 3D, compression formats that seem to change over and over again causing in players on computers that can’t keep up with the formats and asking for an update every month in order to play the next silly video (I do not mean this video). I have some problems with people not using a tripod, but in lot’s of situations that is fully understandable. Today we have to live with crumbled low-res and over compressed videos or super-duper-full-4K videos that slow my computer to a standstill, but how is it possible that in the year 2016 videos can be produced that add a jelly type motion that makes it unbearable to watch. Even if it is caused by motion stabilization software, still somebody must have tested the algorithm and said it was okay to watch, then somebody must have approved the video before releasing it and thought it was okay to watch. Why?


    PS: also audio not being in sync with the video is a problem that was solved in 1927 but nowadays seems to be a new problem. Not only on youtube, vimeo or whatever even (from time to time) on my TV-setup-box, which is supplied by my cable company. Fortunately this video does not seem to have that problem.

    1. For your last paragraph…
      It may be the settings on your tv. My old LCD was really weird; there might be some up-conversation settings or something ridiculous. I went back to a CRT from the 90s after the LCD broke! ;)

      I haven’t watched the ‘jelly-video’ yet, because I just ate.

    2. So the boat that the speedo is going into does not have a can bus or reliable way to measure the speed, thus I went for the satellite option.
      WRT the jello video- I have turned the stabilization off now, and seems to be better- apologies- on first glance it seemed to be doing a good job.

    1. Thanks for that- Had a quick look when I started but didn’t see the stepper with stops. The servos i found generally had less range so decided to go with the tacho.

      1. An alternative is known as an “air core gauge”: Two coils arranged perpendicularly acting upon a magnet with a weak return spring (only used when the power is off). Simple to drive with two PWM channels, used in instrument clusters since the 80’s I guess. The magnet aligns itself to the resultant vector of two magnetic fields – very elegant!

    1. Great idea- could have a threshold and if the IMU gives a value different to the GPS by the threshold amount then use the IMU. Thank you- Version 2 here we come.

      1. I’m just the first to post it, but you’re welcome :) Nice project, BTW.

        Your threshold idea is worth a try, but I thought about it some more, and I think I would use the IMU as the main data source, then correct it periodically with GPS data (when the latter is above a certain threshold, hence probably more accurate), and also use the consensus of the two (IMU: “we just decelerated a lot and are not accelerating anymore.” GPS: “I think we’re basically sitting still.”) to reset everything to zero. It’d help tame the drift most dead-reckoning systems suffer from, and it would at least mostly work in the absence of a satellite lock (e.g. inside a metal building or tunnel).

        Now I’m thinking about the fact that I (and most other hackers) have a few old phones with both IMU and GPS, and wondering how hard it would be to make into an app (although such a thing might already exist). I also have a bunch of those needle-gauge stepper motors mentioned elsewhere in the comments, and I’m wondering if they could be driven from the headphone jack for a power-sipping display solution…

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.