RevK's privacy-friendly GPS logger

I sometimes ponder getting an electric car, but I have concerns about range.

I’m pretty sure that most - the vast majority - of journeys would be fine, but I’m less convinced about some of the journeys we do regularly.

What I’d like is some actual data, on which to base decision making.

To do this, I’d like to log, automatically, our journeys.

I didn’t want a phone-based approach

I could use a phone-based logging system for this, but I don’t really need a log of everywhere I go, and the vast majority of times I am not driving, and so would be generated unnecessary data.

Similarly, I don’t want something which requires Sandra and me to remember to start the logging, as we’ll inevitably forget.

I could, perhaps, have bought a second-hand Android device, and used that, but I’m not aware of an Android device which will start automatically within a couple of seconds of starting the car - my Pixel takes considerably longer than that to boot - or an app which will automatically start logging GPS coordinates.

Finding dedicated hardware was hard

What I wanted was a dedicated device, which I could leave in the car, and which would start logging automatically, and which would upload the data, to an endpoint under my control, automatically.

No “cloud” elements, no registration elements, and ideally Free software-based.

Looking around, I couldn’t find a device which did quite what I wanted.

There are lots of GPS loggers, but the vast majority would upload only to the manufacturer’s cloud.

None used Free software.

RevK’s custom IoT GPS logger

Photo of a small circuit board, with green and yellow LEDs indicating satellite status, in my hand

If you don’t already know RevK, he is, without doubt, one of the most talented - and hard working - people that I know. I’m delighted to call him a friend.

Recently, RevK’s projects have involved him designing, and having custom made for him, his own circuit boards, usually based around ESP32.

RevK very kindly offered to make me a GPS logger, and that has become his most recent project.

The utterly amazing thing is that, within about a week, RevK had not only designed the hardware, but had manufactured boards in his hands, running software.

(Actually, the even more amazing thing is that RevK thinks that he was slow in taking this “long”…)

I received a prototype board earlier this week, and It Just Works.

It is exactly what I wanted:


Setting it up was a breeze, and within a few minutes I had it logging GPS data and uploading it to a web server I run.

Using RevK’s json2gpx tool, I can convert the GPS logs into .gpx format, which is useful for visualising it.

For my needs, I can probably just use a json parser to extract the information I need from the raw files - just dates, times, and distance travelled - but overlaying journeys on a map is fun.

I think that RevK’s plan is to sell these (probably on Amazon) some point soon-ish.

Photo of a small circuit board on the dash of a car. It is connected to a blue USB-C cable. Connected to the circuit board, by a thick-ish green cable, is an even smaller circuit board, the GPS receiver.

I’ll need to sort out a small housing for the device, and attach it more robustly to the car - I don’t want it flying around in the event of a crash - but I am so unbelievably impressed with this, and I wish I had just a fraction of RevK’s talent (and experience, and hard work, and so on).

I could also be very tempted to fit one to my bicycle, but this time just for fun!

Spousal privacy

Sandra (my wife) and I had a good chat about this, before I pushed ahead with the project.

We can already - via phones and Home Assistant - see each other’s real time location, as well as various factors linked to our home such as when a door was opened and so on.

Sandra can also see when I am on a phone call, wherever I am.

So, although everything is under our (and, realistically, that means “my”) control, we have quite a surveillance-heavy, or surveillance-possible, life.

(We also live togther, work together from home, spend our weekends doing stuff together, and so on, and aren’t massively sociable, so we spend pretty much all our time together. Other than running errands, if one of us wants to know where the other is, chances are it means looking in a couple of rooms and finding them…)

But, as far as I know, I don’t have historic logs of Sandra’s (or my) location, in the way that I would have with these detailed GPS logs, so this was something sufficiently new to be worthy of a conversation.

We are both interested in the possibility of an electric vehicle, and so having this kind of accurate data is helpful. But I might, assuming we don’t find the mapping useful, write some code to extract the information we want and then delete the detailed journey files, when I next get some free time.

[Update: RevK is now selling them via Andrews & Arnold, in the UK.]