FoxLAP – The DIY version

This FoxLAP DIY tutorial has continued to evolve since its first publication in late 2021. The instructions have been updated while preserving the original ESP-32 Dev Kit C V4 build. For reliable GNSS reception, this tutorial uses the proven MatekSYS SAM-M10Q, which remains fully supported and works perfectly with FoxLAP DIY.

At the end of this tutorial, you will have a fully functional GPS lap timer.

It does, however, come with a few limitations. This DIY version is intentionally focused on the essential GPS lap-timing functions. It is not designed to be fully water-resistant and uses a simple physical power switch instead of an advanced battery-management system.

And yes, the inside is going to look a little rough, with hand-soldered wires and hot glue!

This is intentionally a quick and simple implementation. The first FoxLAP prototype was built in almost exactly the same way so that I could start developing the firmware. I rebuilt one for this tutorial without spending too much time trying to make the internal assembly perfect. I’m sure many of you can build something cleaner — and if you do, please share it!

Despite these limitations, you still get the essential FoxLAP features: lap timing, gap to best lap, speed, sectors, theoretical best lap, live delta and session recording. You can also analyse your recorded GPS data afterwards using GPXRender software or with the online tool

The goal of this tutorial
The aim is to build the simplest possible FoxLAP device using readily available components. This is very close to the hardware i originally used when I started developing FoxLAP, so rebuilding it for this tutorial brings back a few memories

Is it the ultimate hardware design? Definitely not. Could some components be replaced with better or cheaper alternatives? Of course.

Why Blender? Why this display? Why this ESP32 board? There are plenty of choices that could be debated or improved. But this version exists, it works, and it is relatively easy to reproduce.

So, ready to build one?

1- Required parts

This is what I used, mainly because I already had most of these items at home. Some of these parts can be replaced with more convenient or cheaper alternatives, depending on what is available in your country.

I have included links to purchase the components, but I have no affiliation with these sellers and I do not earn anything from these links. You are of course free to buy the parts wherever you prefer.

• 1, ESP32 ESP-WROOM-32 development board. Used: ESP32 Board (Usually around 5$ per unit)
• 1, Lithium Battery Charger. Used: Shield Wemos D1 Mini ESP8266 (1$)
• 1, GNSS Module. Used: Mateksys SAM-M10Q GNSS module (36$)
• 1, display. Used: JLX 256×128 COG 5V White SPI (12$)
• 1, sdcard module. Used: Micro SD Card Shield (0.50$)
• 1, 18650 Battery. Used: 18650 INR18650-35E Samsung Li-Ion 3,7V 3450mAh (6$)
• 2, 10K resistors
• 4, 1K resistors
• 1, power switch. used: 2 position mini switch (6$ for 100 units)
• 1, micro sd card. Used SanDisk 16G or Verbatim 16G (5$)
• 4, push buttons 6x6x4mm. Used buttons
  
• Hot Glue and regular glue
• Wire wrapping. Used: link
• 6 M3 16mm screws
• 1 M8 30mm screws
• 2 M8 flat washer
• 4 M1.2×5 screws
  

More & important informations:

1- GNSS module: this tutorial is designed to use the MatekSYS SAM-M10Q mounted inside the enclosure. However, you can probably use any genuine u-blox GNSS module. Please avoid very cheap GNSS replicas. A $5 GNSS module is unlikely to provide the accuracy and reliability you want for lap timing. You can find cheaper genuine u-blox modules such as the M8N, but you will be limited to 10 Hz. That is still perfectly usable — for comparison, the Alfano 6 GNSS also runs at 10 Hz. With some M8N modules, you may not be able to install the GNSS receiver inside the enclosure, so it will have to remain external. In that case, you will need to adapt the 3D enclosure model. I already have a few 3D models designed for this type of configuration.
I had good results with this u-blox M8N receiver:
https://www.aliexpress.com/item/32748573256.html

At the moment, this project is only compatible with u-blox GNSS chips. I may add support for other GNSS modules in the future if they prove to be reliable, accurate and affordable. Some users have also successfully used the QUESCAN M10Q.
Note: on first startup, FoxLAP attempts to communicate with the GNSS receiver at 9600 baud. Depending on the module you use, you may therefore need to configure the GNSS receiver before installing it.

2- Display: this JLX 256×128 COG is available in both 5 V and 3.3 V versions. I used the 5 V version simply because I already had one. The battery shield used in this tutorial includes a 5 V boost converter, so I used it to power the ESP32, the GNSS module and the display. You can also use the 3.3 V version of the display, but obviously do not connect it directly to 5 V. I chose the white backlight version simply because I prefer white backlights.

Important: the display must be the SPI version.

3- MicroSD card: the ESP32 cannot directly use FAT32 partitions larger than 32 GB, so I recommend using a card of 32 GB or less. If you use a larger card, you will first need to create a 32 GB FAT32 partition on it. For this project, even 16 GB is already more than enough. As with the GNSS module, avoid cheap no-name microSD cards. They can cause all kinds of read/write errors and intermittent problems that are extremely frustrating to diagnose. I have already wasted far too much time with cheap cards before eventually throwing them in the trash! Use a reputable brand and save yourself the headache.

4- 18650 battery: again, don’t be fooled by unrealistic specifications. Avoid no-name batteries advertised as 12,000 mAh or similarly impossible capacities. Use a good-quality 18650 cell from a reputable manufacturer. The battery’s positive and negative terminals must be flat.

With batteries that have a raised button-top terminal, it may be difficult or even impossible to fit the battery into the slot provided in the enclosure.

2- 3D Print

• STL files were created using Blender.
• 3D Printer: Creality CR10s PRO.
• Slicer: I used Cura to slice the 3D models
• 3D filament: i used the 1.75mm ZIRO Filament PLA with carbon fiber. Amazon link: https://www.amazon.com/dp/B01IICFS4Y/
• Print settings: 0.4mm nozzle, Standard quality (0.2mm), 40% infill, Support (zig zag support)
• Print Speed: Usually I set the speed to 60% of the maximum speed the printer can achieve. Because I saw that the more I increase the speed, the more faulty prints I get.

I’m not a 3D-printing expert, but I got my best results by printing the STL models this way. In the screenshot, I assembled all the STL parts together only to show you how they are positioned. In practice, I printed each STL part separately, not all together as shown in the imagem.

There is also 2 other parts printed with flexibale filament. You will need two M8 flat-washer parts. They will help you mount the lap timer securely to the steering wheel. This filament gives very good results, but it is quite expensive, and you probably won’t want to buy an entire spool just for two small parts. You can try printing them with regular PLA instead.

Here is the STL files you must print:

3- Assembly guide

From this point on, you should have the 3D-printed enclosure and all the electronic components in front of you. Here is the complete wiring diagram. Even though the circuit itself is quite simple, it requires a fairly large number of wires.

3.1 Buttons assembly
Insert the four buttons into the button holder you printed earlier.

Make sure the buttons slide freely without binding. Enlarge the holes slightly if necessary, as 3D printing can sometimes leave a small amount of excess material around the edges.

Then attach the button-holder parts using M1.2 × 5 mm screws. Repeat the same process for both the left and right button assemblies.

Connect all the button ground pins together, then connect them to the display’s K ground pin. Use a different wire color for each button. This will make it much easier to identify the correct wire when you solder them to their corresponding ESP32 GPIO pins later. It’s time to add the 4 debounce resistors on the buttons.

IMPORTANT: you may not have to add the debounce resistors (even if it’s not recommanded). But you must add them if you are willing to use the device in engine environnement

Apply hot glue to all solder joints. Remember: vibration is our enemy. Leave enough length on the wires, as you will need to solder them later to the ESP32 located in the other half of the enclosure.

3.2 Display assembly

Install the display and secure it with the screws. You can add a small amount of hot glue to help position the display correctly and make sure it does not move.

Here is how the display should be connected to the ESP32. Prepare and solder the wires to the display, but do not solder them to the ESP32 yet. Again, leave enough length on the wires, as you will need to connect them later to the ESP32 located in the other half of the enclosure.

3.3 Bottom part assembly

Place the power on/off switch and hot glue it.

Insert the M8 × 30 mm screw, apply a small amount of regular glue to the top of the screw, then tighten it into place.

Fill the remaining space around the M8 screw head with hot glue to secure it firmly in place.

3.4 Battery assembly

Now take your 18650 battery and use a spot welder to attach nickel strips to both terminals.

Place the battery inside the enclosure and apply hot glue around it to hold it securely in place.

Follow this wiring diagram to connect the lithium battery charger

You should now have something that looks like this.

Make sure the power switch is OFF during the following steps.

At this point, you can also check that the battery charges correctly and verify that you can measure approximately +5 V between the 5V and GND pins on the lithium battery charger board. The two 10 kΩ resistors connected across the battery terminals will allow us to estimate the battery level using the ESP32 ADC. This is clearly not the most accurate way to measure battery level, but remember: this tutorial is intended to build a simple and inexpensive version of FoxLAP. It will still give you a reasonable indication of the remaining battery level.

3.5 GNSS assembly

Take your MatekSYS SAM-M10Q GNSS module. Prepare the required wires and solder them to the module according to the wiring diagram.

Important antenna position: the GNSS antenna must always face the sky. Nothing may cover or pass over the antenna: no cable, electronic board, display or other component. Only the plastic of the enclosure should be above it.

3.6 SDCARD assembly

3.7 Wire to the ESP32

The SD card reader module I used here is not exactly the same as the one listed in the parts section. The one shown here is actually too large for this build, but it was the only module I had available when I recreated the DIY device for this tutorial. I didn’t want to buy another SD card module just for that. Use the SD card module listed earlier in the parts list. Alternatively, you can also use a microSD-to-SD adapter as the card holder — yes, it works.

Now solder the wires to the corresponding ESP32 GPIO pins.

It’s starting to look pretty ugly now, isn’t it? 🙂

Now connect the display and button wires to their corresponding pins on the ESP32.

(Only after Point 4 and 5 have been completely done)

But before closing the box, you have to flash the board with the firmware. See Point 5. Firmware installation to do it.

Close the enclosure and secure it with six M3 × 16 mm screws.

Then glue the front panel into place. I printed mine in yellow, but of course, yellow is not mandatory! 🙂

It should be working now… And it definitely looks better once you can’t see what’s inside. 😄

Obviously, the dedicated-board version is much easier to assemble. It also includes a larger display and many more features. If you are interested in the dedicated-board version, you can find more information on this page

4- Prepare your SDcard

Partitions larger than 32 GB will not be recognized by the device. So if the SD card is not detected, make sure that:

1. You are not using a poor-quality, no-name SD card.
2. The partition size is 32 GB or less.

If your SD card has a capacity greater than 32 GB, you will need to create a 16 GB or 32 GB partition. Any remaining space on the card will not be used.

Format the SD card using the FAT32 file system.

Once the formatting is complete, the SD card will be empty and ready to be inserted into the device.

5- Firmware installation

Download this zip file containing the firmware and the tools to flash the board.

Version 2.14 – release date 2026/05/20
What’s new in version 2.1X:

• Gui mais rápido usando SPI de hardware
• Controlador conduzido
• Correção de erro no gerenciamento de pistas
• Fix Bug in Live Delta for custom tracks

5.1 Flashing on windows operating system

Unzip the contents of the downloaded archive. Connect your ESP32 board to your computer via USB, then run the flash_firmware.bat file.
You will be asked to enter the COM port used to communicate with the board. Enter it like this:

COM6

Of course, if your board is using a different COM port, replace COM6 with the correct one. And please don’t contact me just because COM6 is not recognized — your board may simply be using another COM port. 😄

Or you can enter directly the following command

esptool.exe --chip esp32 --port COM6 --baud 921600 --before default_reset --after hard_reset write_flash -z --flash_mode dio --flash_freq 80m --flash_size 4MB 0x1000 foxlap.DIY.bootloader.bin 0x8000 foxlap.DIY.partitions.bin 0xe000 boot_app0.bin 0x10000 foxlap.DIY.bin

Now Hard reboot the board. OK, now the device must be working…

5.2 Install a new firmware on an exising and running device

Start your FoxLAP device, then go to:

WiFi transfer → Start WiFi

If you have not yet set a WiFi password, go to:

WiFi transfer → Set WiFi password

Your password must be at least 8 characters long.

Once this is done and the device is running in WiFi mode, you should see “WiFi Data Transfer” on the screen, along with the name of the hotspot created by the device, for example:

FoxLAP_xxxxxx

On your computer, connect to this WiFi hotspot. Remember that WiFi passwords are case-sensitive. Then open GPXRender, available on this website, and click “Synchronize device”.

If your computer is correctly connected to the FoxLAP device, a window will appear. Go to the Firmware tab, select the new firmware file, then click Flash. You can now update the firmware over WiFi without having to open or disassemble the device.

6- First launch and configuration

At the first launch, you must get this screen. If it is not already done, create a FoxLAP account here
You will need to enter your name, choose a password, and provide a few other details. Some characters are not allowed, so please pay attention when choosing your login information. You will need to enter the same information directly on the FoxLAP device, and since screen space is limited, I had to restrict the list of supported characters.

Only these characters are allowed at this time: 0-9, a-z, A-Z, ! # $ % & ‘ ( ) * + , – . @ : ; =

What you need to enter during the first startup is shown in this video. The device must be able to connect to the Internet, so you will need to enter your WiFi credentials. You may have trouble with WiFi passwords containing special characters that are not supported by the device. In that case, you can share your phone’s Internet connection by creating a mobile hotspot with a password that only contains characters supported by FoxLAP.

If the connection is unsuccessful, turn off the device and restart it to try again.

Once the connection is successful, the device will automatically retrieve the settings stored in your account, which are available on this page https://foxlap.com/mydevice.php

You will be able to change the device settings and also select or unselect the tracks available on your FoxLAP. Do not select all tracks. Only select the tracks from your country or the ones you are likely to use. The more tracks you select, the longer the automatic track detection may take. After changing your track selection, don’t forget to click “Save Track Selection”.

Then, on the device, go to the “Synchronize” menu and select “Update Track Database”.

What to do if your track is not available on the device?

I recommend creating your own track using the tool provided here: https://foxlap.com/track_creation.php

Once the track has been created, go to https://foxlap.com/mydevice.php, select your newly created track in the “My Own Tracks” category, then click “Save Selection”. Then, on the device, go to the “Synchronize” menu and select “Update Track Database”

A few tips:

I will add more information and tutorials explaining how to use everything. But please keep the following points in mind:

• There may still be some bugs. The DIY firmware is a fork of the dedicated-board firmware, and I have not tested every feature on this DIY version, as I do not personally use it.
• I cannot predict how good the GNSS reception will be at your location. Here in France, the signal quality is very good. In an upcoming firmware version, I also plan to add an option that will allow you to select the SBAS PRNs yourself.
• Before heading out onto the track, turn on the device and make sure the GNSS reception is good. In the bottom status bar, you should see at least 12 satellites, and the HDOP (Horizontal Dilution of Precision) should preferably be below 1.0. Around 0.7 or lower is ideal; here in France, I often get values around 0.6.

Turn the device on and leave it stationary for a while before driving, to allow the GNSS receiver to obtain a good and stable position fix.

I have one important requirement regarding commercial distribution: you may not sell this DIY version. Commercial use of the DIY version is not permitted.

That’s all for the moment,
Renan BROQUIN

Download FoxLAP User Guide

https://foxlap.com/dl/foxLAP-UserGuide.pdf

This is what it looks like to drive with FoxLAP1:

This is what it looks like to drive with FoxLAP2:

DIY Builds from the community:

LED strip add-on

Optional

Add a standard WS2812B addressable LED strip to display sector performance and live delta information. Update FoxLAP to the latest firmware before enabling it.

• LED typeWS2812B
• LED count3 to 15, default 5
• PowerRegulated +5 V
• ControlESP32 GPIO12

Connect the strip ground to FoxLAP GND, its +5 V input to the 5 V rail and its data input to GPIO12. GPIO12 is safe here because the firmware does not drive it HIGH during boot. Select the number of LEDs in the FoxLAP settings menu.

Available DIY display modes

1. Disabled: no LEDs.
2. Sectors: one LED per sector, red or green according to the result.
3. Live Delta: red or green when behind or ahead.

Mechanical work required: this add-on is optional and is not integrated into the supplied FoxLAP DIY enclosure files. You must adapt the STL model yourself to create the LED opening, support and cable routing for your chosen strip.

Open the original FoxLAP LED Strip Add-on tutorial.