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GPS Lap Timer Project

[OUTDATED – this is the genesis of this project]

This project aims to create a low-cost, high-accuracy GPS Lap Timer for racing purposes.

1 year ago, my 11 years old son started GoKart competition. As an engineer, i am always looking for new challenges, that’s why i decided to create my own GPS LapTimer – I Know, MyChron or Alfano Lap Timer already exists, but, even if i have never used them, they are expensive – And why buy something that i can build and program?

So, to answer to the question “Did i manage to build a reliable and high-accuracy GPS Lap Timer?” YES, i think i did it. And here is the result:

EDIT: I renamed it FoxLAP. LapKiller as you see it on the screenshots is no more used.

See what it looks like in this short video:

The device used to make this video has been used by my son for several months. It’s not a brand new device out of the box, but you see what it looks like after being used for real.

Ok, i know what you are thinking… “he made something cheap but i think it will not be as reliable as MyChron or Alfano or Speedhive”. In fact you are wrong. Let me show you (if you are still here) how reliable this little device is:

Here are the lap times from the same race session recorded by both a Speedhive myLaps transponder fitted to my son’s kart and my homemade Lap Timer.

SpeedHive recorded lap Times
LapKiller recorded lap times

The highest gap is on lap 5 with a 0.012 second gap. Not bad, i think. Times recorded under heavy rain and wind.

I made a dedicated data analysis tool directlty working with the device:

FoxLAP recorded data – Online tool analyzer.

Already more than 1600 tracks automatically recognized by the GPS LAP Timer

2- Functionnalities

  • 25HZ high-accuracy GNSS: GPS position updated every 40 milliseconds using a ublox GNSS receiver.
  • Replay: play saved sessions on the device and see how fast was your lap
  • Multi user: User interface to manage users (creation, selection)
  • Multi-engine measurement on the running time of your engines.
  • Real time speed, bearing, position on track monitoring
  • Track auto detection based on your location
  • Gopro compatible: paired with your gopro, FoxLAP will start the video recording when you cross the start line and will stop the video record at the end of your session. You will be able to see your laps in video synchronized with the recorded data with the online tool.
  • Wifi server: Transfer your sessions data to your computer/mobile over wifi. (GPXRender, the software i made to analyze GPS data is able to directly connect to the LapTimer device).
  • Synchronize recorded data with the dedicated online tool i created where you can store your sessions and analyze your data
  • RPM and water temperature sensors
  • An 8Gb sdcard: 1 session file is 1.5 MB on average. So 8Gb will let you store 5500 sessions before running out of memory (you will be forced to delete your old vintage sessions on the device)

3-Inside Components

This GPS Lap Timer is based on an ESP32 board – A low-cost, low-power system on a chip microcontrollers with integrated Wi-Fi and dual-mode Bluetooth. The dual-core Tensilica Xtensa LX6 microprocessor is a major advantage for the goal. In fact, one thread is dedicated to monitor the GPS position without any interruption. A 3500 MAH 18650 battery allows to record several hours of data.

Bill of materials
See the tutorial on how to build a simple version of this device: here

The plastic box enclosure is a 3D printed model i created with blender. It can be printed by yourself. On my side, i decided to make it printed by professionnals as the result is way better.


Here is a video showing how to setup the device on a goKart. This is my son’s gokart, OTK with rotax J125 engine.

This is the end of this small presentation of my attempt to create a low-cost, high-accuracy GPS Lap Timer for racing purposes.
I don’t know who other than me finds these kinds of projects interesting, but it was a lot of fun doing it. Leave a comment if you have any questions about this project…

May 2023: update

– RPM and temperature sensors are ready
– I have made a dedicated Board for this Lap Timer. Important for reliability, there is a lot of vibration and self made soldering may be a problem. i just received the first boards and they are working like a charm
– I am producing 10 units, that will be tested by young (and some less young) drivers in my area. I’m pretty sure i will have some interesting feedbacks in order to improve this little device.

– This device is able to connect to any wifi hotspot (your mobile phone can be a hotspot); so the device will send automatically your sessions and synchronize to your account on an online tool i have made (still working on it but almost done). Settings, tracks, data anaylzer are directly on the website – the device is synchronized with your account – i think it’s nice. here is a demo (Work on progress):

June 2023 Update:

final correction on the RPM sensor…

July 2023 Update

– working on a new board version including gyroscope and accelerometer.
– I have worked on the data analysis tool to configure sectors and see sector times. What do you think about that? what do you think would be interesting to add ?

We will be at Kartmag Trophy that will occur on 18-20 august 2023 at Varennes sur Allier (FRANCE). my son will race in Rotax. Maybe some you will be there too.

September 2023 Update

back from a big race event, it was obvious for me that i had to improve the data analyzis tool. We were discovering the track, only few sessions for practice. So here’s what I added that would have been nice to have during the event:
– real time gap between laps,
– save/load laps from different sessions
– and of course video overlay. i know during the race, video is not allowed but during practice sessions, it is allowed… and it helps a lot

November 2023 Update

1- I tested installing both an Alfano 6 and my device on my son’s goKart and recording the same session. Both with RPM sensors. I wanted to see if the recorded RPMs were the same. Here is the result :
– Brown: Alfano RPM record
– Blue: My Device RPM record

RPM recorded are almost exactly the same. Alfano pick a value every 100ms, i pick a value every 50ms.

2- i’ve made different box enclosure models. One without external sensors for Rental gokarts (only GPS inside); One for those who wants to get the GPS sensor inside the device but with external sensors (temp/rpm); and one with external sensors (temp/rpm) + external GPS sensor.
What i can say for sure is that external GPS sensor is better, the signal is better and when it’s time to upgrade the GNSS module for a newer and better version, you don’t have to buy again a complete device… you just have to plug your new GNSS receiver and that’s all. On my side i use the external GPS sensor (for all the reasons already explained).

3- I’ve made complete tests with water. The device must work under heavy rain and must not be damaged, i’m sure you agree. The first test was not good, after several water exposition (deliberately outrageous tests), some units have suffered small water infiltrations. I had to correct this issue. After modifications, the second test was more conclusive and I didn’t see any faults. The test consists of leaving the device in the shower with a high flow rate 🙂 i have to conduct more tests like impact resistance – i plan to drop a unit from 20 meters high and see what happen 🙂

4- Water resistance update: November 14th. We are coming back from a race week-end under heavy rain. No issue at all with the lap timer 🙂

Another November update

  • There is already more than 1500 tracks automatically recognized. If your track is not recognized, the device is able to “learn” a track if you drive on it for 1 lap. But i have not enough feedback on this functionnality – ok – i have tested it on 4 or 5 different tracks but it’s not enough to validate and maybe it can be buggy in some cases not yet encountered.
  • That’s why i added a simple tool to create your custom tracks. less than 5 minutes to add a new track on the laptimer.
  • You can see it in this video:

I’m preparing a tutorial on how to make a simple version of this device. it will be a way to start something, because material things take so much time. This version is the cheapest version we can make and it is obviously based on a development board. it will allow the most motivated among you to be able to test a simple version.

70 thoughts on “GPS Lap Timer Project”

  1. Hello, good afternoon, congratulations on the project, it was excellent.
    My son is also starting out in Karting, and as you said, the equipment is very expensive.
    I found your project interesting, and I would like to know if you could help me in the construction, or if you are selling the
    LapKiller. I’m from Brazil and here it’s much more expensive to buy an Alfano. Sorry for the English, I hope you can understand.
    Thank you for your attention.

    1. Hi Tonny,
      I’m still working on it. Now i have working RPM and temperature sensors. 1000 tracks automaticaly recognized by the box (and still adding new).
      Yes i know these things are expansives and my goal is to provide something affordable. I’m finalizing the PCB to offer something reliable. in less than 2 months I will have something to share

  2. Hi, your lapkiller project looks amazing!! My Sons have started karting as well, and I am now looking at lap timers. I like building things myself and started researching the possibilities of building a timer, hence coming across ur page. I dont have the programming skills to do this, but have the electronics and 3d printing side of it. Very much a novice programmer. I would love to build a this for my Sons. If u are happy to share how to build it? Is there a way I can contribute to ur project?

    1. Hi michael,
      I know well what it means for fathers when your sons starts gokart (lot of time, energy, lot of money). My goal is to provide professional, affordable and reliable alternative and give users control over the project. The final PCB is now ready to be produced. i will share the box 3D model also. and everything cost a fraction of what cost lap timers available on the market. Stay tuned, everything is going fast now on ths project

      1. Hi,
        haha Indeed it takes alot of all of those things – I have very much become a track Dad, and seem to spend my days carrying water and taking helmets off heads… I did decide they cannot have all the fun, so I obtained something for myself as well!
        Look forward to building your lap timer! Your project really has me excited! looking forward to it, and being able to expand and test as well. I live in an area where it is hard to get components, so typically need to import everything, is the list of components in ur original post still the recommended? If so I will start ordering those components in the interim so I have them.


  3. Hi,

    Any chance you can share the code? Quite interested to get this up and running, and so far this is the only project with an actual usable interface. Currently using my hardware for BonoGPS but this project of yours has turned out amazing!

  4. Hi,
    I’m a semi-pro karting driver from india and in my country there’s a real shortage of even ready made devices and ready made devices after taxes go upto a 1000$ here.

    Could you please share the code so I can get this up and running, I have a couple of events coming up and the real time delta per lap will really help me analyse and improve.


    1. HI Andy,

      thanks for your interest. the work is still on progress. I am now closed of having a fully functional hardware with sensors+software solution. stay tuned

  5. That is great! Waiting for the final release. I will use it for my minigp. Do you have a plan to make 2 versions then: 1 full (with revmeter) and 1 lite? AWESOME JOB!! 👍

  6. Hello, looking for devices for karting telemetry that are as cheap as possible, I came across this website.

    I am interested in the project that you are carrying out and I would love to be able to purchase it as soon as you have finished it, thanks from the entire community because the prices that are around the devices today are exorbitant and people who are in the world for a hobby are not We can afford such a large expense.

    A hug friend,
    Excuse my English, I’m from Spain

    1. thanks for your message junma.
      This project was designed and carried out with the objective of obtaining the best quality at the lowest possible price. I want it to be upgradable and easily fixable, the world has changed and it’s no longer acceptable when a broken screen or an outdated gps chip, the whole device goes to trash. Yes, this device will not be the prettiest on the market, but it will do the job as well or even maybe better without breaking the bank. I will keep you informed of the progress

  7. Hello from Australia! Congratulations on putting together such a fantastic project. I love these sorts of home-made projects and this really is top level. I cannot wait to see the final item when you are ready to release. As a motorcycle rider, I would love to see this adapted so I could use on my motorcycle when I go to Phillip Island MotoGP track and wish to be like Fabio Quartararo! Thank you again and keep up the great work.

    1. Greetings from Australia and hope you are recovering well from your surgery. I have been following this page and looking forward to the updates as you have been making them.

      Can I purchase a unit from you please and help with testing? Thank you again for all your great work and looking forward to hearing from you soon.

  8. Hi, been following and checking your website regularly for any updates. Was very excited to see your progress. What you are creating looks amazing and what an amazing job!! I look forward to being able to build one in what looks like the nearish future! Great job on the demo looks super awesome. Happy to help and contribute where I can.
    have a good one!

    1. Entre français, nous pouvons utiliser notre langue. ca avance vite désormais. la PCB (carte électronique), que je viens de recevoir est 100% fonctionnelle. J’ai fait une carte pour éviter les problèmes des soudures qui lâchent – les vibrations au bout de quelques mois d’utilisation des prototypes ont causé une panne avec une soudure qui a finie par lacher – avec les pcb, plus de soudures qui lachent et ca offre la possibilité de dupliquer ce compte-tour tres rapidement et facilement. je finalise désormais l’overlay (la couche supérieure qui contient les boutons) car celle que j’ai fait est spécialement conçue pour mon fils qui cours avec le numéro 21, j’en fait une plus générique qui puisse satisfaire tous ceux qui seront intéressés par le projet. l’avantage de l’overlay c’est qu’elle offre une résistance à l’eau contrairement à des boutons qui seraient installés sur le boitier… bref ca avance. Merci pour l’interet en tout cas. 1er message d’un francais 🙂

      1. Bonjour,
        Un autre message en Français ! 😉 Super projet, félicitations ! Je suis encours de préparation d’un petit prototype 2 roues pour rouler sur piste de karting. Votre projet m’intéresse, si vous le commercialisez ou souhaitez un béta testeur, je suis partant. Bonne continuation. Gildas.

  9. This is an awesome project. I had been independently gearing up to make essentially the same project for a bit now. Even down to an esp32 and ublock m8n.

    Is there any plan to make the code or HW design files available. MY day job is embedded development so I’d be happy to try to contribute back with software features/fixes. The HW design part was the part I was least looking forward to and probably why I was dragging my feet starting the project.

    I’d be happy to pay for beta unit to play with.

  10. Hi there,
    I currently work for an international Karting team. (At both world & European championships .)
    I have been looking to doing something similar before stumbling across this.
    I would be very interested in purchasing a unit to test and give any feedback required. We currently have over 60 gps data systems and have good experience/understanding with telemetry.

    Please contact me if you’re interested.
    Best Regards

  11. Félicitations pour ce super projet qui peut rendre la télémétrie accessible aux petits budgets et aux personnes qui font du Loisir.
    Est-ce dans vos projets de commercialiser le dash ou n’est-ce qu’un projet pour accompagner le petit?
    Je vous souhaite beaucoup de succès dans la suite du développement

  12. Awsome piece of work, I’m intrested to test it as it is, in this phase of the project. I have a 10 years old kid who is racing in karting competitions. I am an engineer too and I started to work at something similar, but this is better than I could ever imagine.

    1. Thanks for your message. i can only make 10 units at this time – i have only sourced components for 10 units. And the other thing is that i had to modify the RPM sensor cause it appears that sometimes i had some noise (EMI: electomagnetic interference), and this is something i must solve. i don’t want to show something with bugs 🙁 – i’m waiting for the new rpm sensor circuit and test it on tracks with various engines.
      Once it is ready i will be open to send units for those who wants to try it. Will be done after these first 10 units test. I need 3 weeks to source all the required components, i only picked easy to find components, so i don’t think that it will be an issue to build more units.

      1. Hola Roquin!

        I would be willing to buy 2, one for me and one for my brother.

        I have a rotax and my brother a subaru 4t.

        Every day I go to the web looking for something new hehe

        We would be very grateful to be privileged to acquire 2 units

        1. Thanks for your support !
          Where are your located Juanma? Subaru 4T is a very specifc engine. My son is training where Subaru 4T is born (Biganos, France).

          1. We are from Spain, specifically Garrucha (Almería)

            I would really appreciate it if we could contact you to buy 2 units 😀

  13. Hello from Spain!

    I would like to get the proyect files to create one or, if not, to be able to buy one!
    Please do not hesitate to contact me!

    Best Regards

  14. I’m so said that you will take a break for sugery. Wish you a speedy recovery and I hope you will be able to continue this great project as soon as posible. I still hope that I will be one of the 10 lucky customers that can buy the initial product.
    I see that you managed to read the rpm, I had good result using the first schematics from this link: https://…..

    1. hello! an amazing project!! I would be interested in buying or testing a unit on a pitbike, no problem with the support, I can design a custom one for my pitbike in 3D.
      we mount zs190 engines.

      I follow you!
      Greetings from Zaragoza Spain.
      @pitbikezaragoza is our instagram.
      good recovery!!

  15. Hi, found your project when I was just googling around if someone has done the same that I was planning to start as a hobbyist those mychrons and alfanos are a ripoff for the sunday driver like me. Nice work with the great looking little device you have there.

    Question is are you going to release this as an open source project with schematics, pcb layout, stl and code?

    If not thanks anyways to encouragement that it really can be done.

    1. HI Asko,
      thanks for your message. it took me hundreds of hours to achieve this. I don’t know yet if it will be open source anq how i will release it. I made it for my son with my son, he have to tell me what he wants to do with this project too; gokart racing cost a lot of money, this project can be a way for him, maybe, to have the opportunity to race. But at this time, i’m not thinking about that, i’m focused to finish it. I wish you good luck if you start this kind of project, it’s a lot of fun when you like programming and electronics

      1. As many said before, I also was thinking of doing my own thing but lacking the hundreds of hours to spend. Have 2 kids racing karts and I know the costs and I think you would be a fool not trying to make a profit out of this to put into your karting. With that said, I would also like the opportunity to access and modify code, adding new sensors (speed, tyre temps, throttle pos, brake pos..) and such and build upon your project. Other from people like me, daytime developers, I think you could have a lot of customers that want to buy complete sets, ready to go out of the box if its is affordable and still be able to take advantage of a open source community that adds to your product.
        I will keep an eye on this project and see what you do in the end. 😉

        1. hi johan,
          i will release it for sure but don’t know yet how, i will not not keep it only for my son. Initially when i started the project, i wanted to make it open source – After hundreds or even thousands of hours of hard work on it and faced with the costs generated by the kart and races, I am thinking about commercial options. But always with the goal to make the device at the smallest possible price.
          i have received yesterday new PCB boards with the Gyro/accelerometer update. All the Softwares are done. i’m almost ready to send devices to those how are interested

          1. As soon as you are ready to share it I would like 2 units. My oldest is racing in RMC and my youngest in a national small chassis series for another year. The season is almost over for us now so we are planning ahead for next season and i would really like to run your device. No pressure though 😉

            1. hi,
              thanks for your support. still in beta phase, i am making changes regarding external sensors, i made improvements to obtain more precise measurements specifically for the temperature sensor. i’ve started to work on the Exhaust gas temperature sensor also. The difference between a good device and a bad one is details and there are a lot of details to master. Obviously I can’t wait to share what my son and I have achieved, but don’t expect a revolution or something that can transform you into a world champion. It is only a GPS lap timer created with the aim of being efficient and inexpensive.
              PS: i made it on my spare time and often around the track where my son is training (dust, mud, cold, wind: dream conditions for an engineer). i know that this project is not evolving as fast as you would like. i’m doing my best

    2. This is an amazing project! Love the work so far, super high quality, very thought through!

      I will keep an eye in this project and hope one day to get my hands on one of those beauties!

      all the best and keep up the fantastic project you have in hands!

      Greetings from Portugal

    3. I have been carting with my father for a while now and I finally got a cart of my own. I am studying Mechatronics engineering and this project has intrigued me a lot. It would be a treat to see how you have connected the various components together and designed the interface.

      1. Hi Dylan,
        The first unit i made was made with development modules. At first, i used the AZDelivery ESP32 Dev Kit C V4, and added sdcard module, battery charging module etc etc. Everything was soldered manually. Even if it works, there was a reliability issue after few months essentially due to vibrations (you can glue everything to try to avoid vibration issues; but once it’s done, you can’t make any modifications or upgrade). The second issue with dev modules is that it takes hours to make 1 unit…
        That’s why i designed a dedicated PCB working exactly as the unit made with development kits, the code is the same (same GPIO are used). No more reliability issues and i can produce units very quickly.
        regarding the interface, everything has been coded in C on the Laptimer device and the telemetry analyzer tool is coded in JS – HTML5/CSS

        1. Thank you for the feedback.
          Is it possible for one to buy the PCB that you have designed or buy the whole system as is?
          I live in South Africa and the prices of the other data loggers are crazy.

    4. Wow very nice I was looking at building something similar to this but always thought the gps wouldn’t be too accurate, looking at this it seems like a great way to get an affordable accurate system.

    5. Amazing work, been following you the last few months. Would be keen to try one on my minigp bike that we run on kart tracks

    6. So how did it go at Kartmag Trophy? Everything is ok with the project? can you start deploying a few pieces for us? We are waiting great news 🙂

      1. The race was great, my son had a great time. the level was very high and he finished far from the top3, but he learned a lot and me too. It was a big event with more than 300 drivers, 72 in rotax natio (my son’s category). and it was a way to improve my device. In real condition, with the stress, the team, you see what is good, what is bad, what you would need… i will post in the next coming days what i’ve changed/added. don’t worry, i’m still on it… it’s a little bit longer than i expected, i know

    7. Hi congratulations I am writing from Venezuela My daughter is starting in the kart I want a Unit and show to my friends a gps lap timer a good price, is available ?

      1. hi, thanks for your message. I would love to be able to send you one unit. I don’t know if I can send a device containing a battery to the other side of the earth, i have to explore this topic and find out how i can do this

    8. I want to buy a unit, I’m from Romania/Europe, you can send it without the battery.
      Can you please contact me by email so we can establish the details?
      Thank you.

    9. Hello from germany,
      It’s a very nice and interesting project you do!
      Do you need an extra gps tool or does it works by itself?

      I would like to by one for tracking my time in rental karts. So the Software can be just for time and track tracking.

      Please contact me!


    10. Would you like to extend the funcionalitis to donwhill and motocross using? i have a rider comunity in Chile, now im thinking in this king of product, i would like to speak more details and work together if is posible, or at least i would like to buy some units, i hope your answear

    11. Hello Roquin,

      I have been following this project since May and would love to purchase a unit from you so I can test and use. Can you please email me so we can organise?

      Keep up the great work and looking forward to seeing a unit for sale 🙂

    12. Abrahan Fernandez Sanchez

      Hello, I’m Abraham and I participated in 4t kart endurance races in Spain. I would love to be able to purchase 1 or 2 devices when they become available, I hope they all work out well for you. By the way, haven’t you thought about making versions of the device with only timing per lap and difference between laps and little else? I mention it because this form could become even cheaper, in addition to opening the range of possible buyers to other disciplines hehehehe, it’s just an idea. I hope much success for you, your son and your project.

    13. Hello,

      Firstly, congratulations on your project, it looks awesome!

      My cousin races here in Brazil in some amateur rental kart championships. He needs a lap timer but the ones bought here in Brazil are very expensive. As I have a little experience with Arduino and automation, he asked me to study the possibility of making a project with a lap timer display very similar to yours. I would like to know if you are willing to share this project with me for my cousin to use when he goes running.
      I’m able to help, test, give feedbacks and help as much as possible with your project


    14. It seems to me that now the project is 100% ready at least from the hardware point of view. Can you begin shipping some units? There is no problem if the project is not ready from the software point of view, I can manage to upload the new software into the device if necessary. As I’ve said before this is the greatest karting telemetry project I have ever seen, I can not wait to test it.

    15. Hi rbroquin.
      Great project, you are doing what many of us are circling around but never get done and seem quite qualified too. But maybe keep it as a DIY kit, this way the price can be kept down and a lot of legal stuff avoided. At the same time users can be invited into further development, i have ideas to do stuff non of the other lap timers do and I am sure others also do. As an open platform only the sky is the limit.
      You are welcome to email me.

    16. Just an ekstra comment, I agree with paul. Hardware seems ready to do some larger user testing, the issues will properly come on the server side of things.

      1. The server side is not an issue and will be able to serve thousands of users at the same time.
        I decided to update the dedicated board, as I will be providing a kit to build the device – I wanted to have something easy to assemble, which is why I made modifications (again).
        the board will be provided with the display directly assembled to the board. Yes I know, if I continue like this, this project will never be finished. at the same time I’m preparing a tutorial on how to build a simple version with development boards

    17. Just checking in on progress – have our second kid needing lap timing with live delta and I really *really* don’t want to buy another Mychron 🙂

    18. Hello from Russia. This is a very interesting project. I would recommend to make it compatible with the racehrono as well. This allowed us to cover a much larger segment than just karting. This would be useful for hobbyists on regular cars or motorcycles. The information that the device registers can be transmitted via BLUETOOTH to the phone in the racechrono application. This application has a very convenient communication protocol that has recently been introduced. I’ll keep an eye on your project too. I would like you to sell the instructions with the code for those who want to assemble it themselves. As a DIY project.

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