Tracer | A Wearable for Things!

The Tracer is an open-source ESP32-based Inertial Measurement Unit tracker

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Have you ever wanted to stick an IMU on a thing to trace its pose and motion? Tracer provides reliable, high-performance, and cost-efficient tracking of objects for various applications. Tracer can be easily mounted using a high-quality velcro strap, allowing it to be fastened on the bicycle's frame for lean and cadence tracking or even the neck of a tennis racquet to count the number of strokes and potentially differentiate between topspin and slice. Let your imagination run wild!

Leveraging on existing open-source projects, the Tracer fully supports integration with Phyphox and can be programmed using Micropython and Arduino. Power users can also use the ESP-IDF tool for maximum customization.


Introducing "Tracer" - a dynamic, open-source project built on the ESP-32 platform. Designed for enthusiasts and innovators, Tracer taps into the vast array of software libraries available for the ESP-32. It offers a unique window into the intricate processes and algorithms behind creating a personalized fitness tracker. This streamlined platform boasts a potent IMU and Time-of-Flight (ToF) sensor to gauge your surroundings, complemented by WiFi and BLE for seamless connectivity.

Before diving further, I have to thank JLCPCB for sponsoring this project. They have been a crucial part of the process by enabling me rapid prototype without compromising quality. All of the PCBAs related to this project were prototyped and assembled by them.  I highly recommend them for the high quality, cost, and time-efficient, if you intend to design and build any boards of your own.

Now back to the project, here are some of the key features;

  • Utilize the LSM6DSL  for real-time object tracking. 
  • Versatile mounting: High-quality velcro straps ensure adaptability, from monitoring lean angles on bicycles to analyzing tennis racquet poses.
  • Efficient on-board Li-ion battery charging via the TP4065.. 
  • Good battery life: Up to 2.5 hours of continuous BLE streaming at 10Hz. Proven 15m BLE range in open spaces, as tested on a tennis court.


  • Microcontroller | ESP32-PICO-D4
    • WiFi | 802.11b/g/n
    • Bluetooth | BLE 4.2
    • FLASH | 4MB
    • Programming | USB over UART (CP2104)
  • Inertial Measurement Unit (IMU) | LSM6DSLTR
    • Accelerometer | ±2/±4/±8/±16 g at 1.6 Hz to 6.7KHz
    • Gyroscope | ±125/±250/±500/±1000/±2000 DPS at 12.5 Hz to 6.7 kHz
  • Li-ion Battery Management | TP4065
  • Power | 700mA 3.3V LDO
  • Mechanical
    • Weight | 20g, including velcro strap
    • Dimensions | 4.2 x 3.6 cm
    • Mounting Options | Velcro Strap or 3x M.2.Screws

Use cases

The test design closely integrates with the Madgwick Filter, facilitating sensor fusion to estimate heading, roll, and pitch. This data can be transmitted to devices like smartphones or PCs for further analysis. Here are some applications:

Real-time 3D Visualisation

This 3D visualization is by streaming data over UART to a simple script written on [Processing]( 

Stream real-time data to phyphox

The real-time plots from the IMU are streamed over BLE to the phone. Data can later be exported over CSV for further analysis if required. This example shows the Tracer streaming the accelerometer data and no. of tennis ball strikes over Phyphox.

Real-time gesture recognition using Edge Impulse

This example illustrates the Tracer's ability to be highly customizable to suit a wide variety of applications and specifications. Using the Edge Impulse platform, I was able to train a neural network that would then run on the ESP32 natively to track a certain gesture or activity. More details on this here.

  • 1 × ESP32-PICO-D4 Microcontroller
  • 1 × LSM6DSLTR Inertial Measurement Unit
  • 1 × VL53L0X Time-of-Flight
  • 1 × TP4065 Battery Management IC
  • 1 × JLCPCB Custom PCB PCB

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  • Final Design Testing & Bulk Order Announcement for Tracer

    YJ08/13/2023 at 14:42 0 comments

    As the "Tracer" project nears completion, we've reached two significant milestones: the final design testing and the preparation for a bulk order. Our rigorous testing phase ensured Tracer's reliability and efficiency. Highlights include:

    • Real-time Object Tracking: Leveraging the LSM6DSL, we achieved precise tracking of various objects.
    • Mounting Versatility: Our high-quality velcro straps showcased adaptability, proving effective on diverse objects from bicycles to tennis racquets.
    • Battery Efficiency: Tracer demonstrated a robust battery life, with 2.5 hours of continuous BLE streaming at 10Hz.
    • Connectivity Range: In open spaces, notably a tennis court, we achieved an impressive 15m BLE range.
    • Use Cases: Integration with the Madgwick Filter allowed for effective sensor fusion, estimating parameters like heading, roll, and pitch. This data was seamlessly transmitted to devices such as smartphones and PCs.

    With the successful testing phase behind us, we're thrilled to announce the preparation for a bulk order of Tracer. This step underscores our confidence in Tracer's market potential. A special acknowledgment to JLCPCB, whose expertise in rapid prototyping without quality compromise has been invaluable. Their support has been instrumental, and for those venturing into board design, JLCPCB comes highly recommended for their quality, affordability, and efficiency.

    As we transition to this next phase, heartfelt thanks to everyone who has supported and believed in this journey. Your feedback and encouragement have been pivotal. Stay tuned for more exciting updates on Tracer!

  • Announcement and project update!

    YJ11/14/2022 at 12:22 0 comments


    Thank you all for the support I have received over the past year. 

    I really appreciate the comments and feedback through this forum and I fully intend to update my content here frequently with useful content as soon as they become available. However due to the format of this platform, it is quite difficult to present small yet important updates, therefore I am creating an Instagram page where I will post my content more regularly and also demonstrate more of the "behind-the-scenes" work that goes into creating my projects. 

    You can access my Instagram page here, elektroThing (@elektrothing) • Instagram photos and videos.  For those of you who do not want to use Instagram, I am also launching my website,, which will serve as the landing page for all things elektroThing. :) 


    It works as a tennis tracker and a data streamer! 

    However, battery life needs to be better and I have a few plans for that; 

    1. Writing better firmware - devising a scheme such that the BLE modem doesn't have to be "always-on" whilst preserving all the features.
    2. Swapping out the MCU maybe? As WiFI is not really needed, I am planning to use a Nordic MCU instead of the ESP32 which should give better sleep currents. 
    3. Design low voltage protection to avoid deep discharge to protect the battery further. At the moment it is only implemented in software.

    Do reach out if there is something on this list that you would like to help with. I am more than happy to send over a board and in return get some work off my shoulders.

  • Back in stock!

    YJ06/20/2022 at 13:20 0 comments

    Hi all,
    I have just received my 30 units and they are ready to be shipped out to you! :)
    You can find them on my Tindie store or through this link. Tracer from elektroThing on Tindie

  • Final Revision (Rev E) Tested and Batch Ordered!

    YJ06/08/2022 at 14:43 0 comments

    Hi all, here's a small but significant update! :) 

    Sorry for the radio silence this past month but I am pleased to announce that I am finally happy with the state of the design and have added a small power switch to improve the usability of Tracer. And with that, I have placed an order for 30 units to be made up, they should be in stock before the end of the month and I will aim to ship them out ASAP from my Tindie store. 

    I am really looking forward to seeing how you will use them and hearing feedback on how the design could be improved further! :) 


  • Using Edge Impulse with Tracer to build your own custom gesture/activity tracker

    YJ05/15/2022 at 09:20 0 comments

    I have been inspired over the last few weeks by Fabio's project with Edge Impulse and how the Tracer platform can be used to leverage the ESP32's processing power to run neural network classifiers of activities and gestures. In this example, I will go through the steps needed to train your own neural network and show it performing live classification with data streamed directly from the board. 

    I wrote an Arduino sketch that would spit out the 3-axis accelerometer and 3-axis gyrometer at a frequency of 100Hz. The experiment I had in mind was basically to use Tracer as a classifier that could tell if it was moving horizontally, vertically, "caterpillar" (move in a jagged way horizontally), and waving. A dataset of 10s was collected for each of the movements.

    Once I had an idea of what I wanted to build, I followed the steps shown in the video tutorial from Edge Impulse in getting a model trained up as well as a k-means-based anomaly detector.

    The initial model that was trained showed inaccuracies when it came to classifying a wave and that is due to several reasons but I think it was primarily due to not having enough data. The table below shows the confusion matrix for the first training cycle with the original dataset.

    Following that, I wanted to see if collecting more data would improve so I spent another 10 seconds collecting data for wave, and it improved slightly. I think more data in each category should improve the neural network's specificity and sensitivity. The accuracy improved across the board while the error rates also dropped.

    Here is a short video example of how the live classification tool is being used on the data that is streaming directly from Tracer over USB (UART). The next step for me is to deploy a real-time classifier for tennis shots that will run on the ESP32 and stream the results over BLE.

    And again as before, really happy to hear any feedback, ideas or suggestions!

  • Register your interest on Tindie

    YJ04/21/2022 at 17:28 0 comments

    Hi all,

    I am grateful for the warm reception, the development units I had sold out in less than 12 hours and I plan to place an order towards the end of the month. Please register your interest if you are keen on getting hold of this;
    It will ship with the board itself and a high-quality velcro strap that can quickly get you started gaining insights. Due to restrictions on Lithium-Ion batteries, you will have to source the LIR2450 on your own but that is quite commonly available and can be found on Amazon and RS for example. 

    Eager to get these boards out there to see what interesting applications can arise through the open-source community! Also, any feedback is greatly appreciated. 



  • Smaller Tracer designed and manufactured

    YJ04/18/2022 at 21:17 0 comments

    Hi all,

    Just a small update with hopefully bigger ones imminent. I have received my new Tracer boards that are now smaller and have a better-suited LDO with a very low forward drop to increase the usable range of battery voltages from the coin cell battery.

    I am currently planning the following activities; 

    1. Testing it out for tennis stroke counting - Done
    2. Tracking bicycle cadence - Done
    3. Using it to synchronize blade strokes at my local rowing club 
    4. Power measurements and optimization - Done
    5. Syncing with camera footage to add data points and improve the usability 
    6. Create a Tracer "hub" to synchronize several modules. Still thinking about the best way to do this as BLE might be a little limiting. Feel free to suggest :) 
    7. Setting up a Crowdsupply campaign to get the hardware out to you! - On Tindie for now

    Thank you all for liking and following this project it means a lot to me and it helps me keep going! 


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jacquline welch wrote 09/05/2023 at 14:38 point

I am wondering if you have developed any methods to compensate for the effects of gravity in terms of acceleration. I am working on a similar project, so please let me know if you have any insights. you can see here

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davidefa wrote 11/09/2022 at 19:07 point

Super interesting! I think a nice feature could be adding a synchronization between multiple sensors ( or simply 'timestamping' data every few seconds ).

Adding 3 sensors for each leg, you may use, for gait analysis...


Did you publish somewhere your esp32 code?


Sorry found software on github:

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YJ wrote 11/11/2022 at 06:56 point

It should be timestamped in the example too! :) 

Would love to know more about your project, is it documented on the public domain yet? 

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IdeaZero wrote 07/20/2022 at 07:08 point

Great one!! 

This is 6 DoF IMU with filters right? how is the yaw drift over time ?  

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YJ wrote 08/24/2022 at 10:53 point

Yes, 6DoF with filters. It is substantial and not good enough for any meaningful dead reckoning algorithms. There will be a 9DoF version that should help with that coming out soon! Using the LSM9

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Alex Nesta, PhD wrote 05/01/2022 at 12:32 point

Hello, are you planning on making your app open source? I have a very similar project and would love to see how someone else implement the Bluetooth data stream.

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YJ wrote 06/07/2022 at 15:37 point

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Zeke Sarosi wrote 05/01/2022 at 08:20 point

Wondering if you have implemented any way to correct for the influence of gravity in terms of acceleration… let me know, working a similar project.

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YJ wrote 06/07/2022 at 15:37 point

What do you mean exactly? With an IMU you can figure out the pose of your "object" that way you know where gravity is.

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parkview78 wrote 04/18/2022 at 03:42 point

Yes, me too, I would love to see your ESP32 code using those sensors  :-)

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YJ wrote 06/07/2022 at 15:38 point

Coming soon! :) 

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Mirko wrote 04/06/2022 at 05:34 point

Fun fact: I am building the exact same thing 🧐

If you want we can have a chat and discuss use-cases and ideas, maybe we can merge our projects.

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YJ wrote 04/06/2022 at 08:01 point

Hi Mirko, your project looks really interesting!  Thank you for sharing.

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Ross Reedstrom wrote 03/23/2022 at 15:26 point

To copy my comments over from reddit - would love to see an open alternative to the Moov Now (look there for additional interesting applications in fitness)

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YJ wrote 03/23/2022 at 15:40 point

Thanks, Ross.

That's my motivation here as an avid cyclist and tennis player.

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Arya wrote 03/22/2022 at 14:49 point

Are the files for this project open-source anywhere? ^__^

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YJ wrote 03/24/2022 at 10:02 point

Hi, Thanks for your interest. I am in the midst of just compiling the files together and adding the necessary documentation — I will update here when it is done.

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Arya wrote 03/24/2022 at 10:05 point

Oh thank you, will be waiting ^__^

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Matias Piipari wrote 04/19/2022 at 07:00 point

I also would be interested of seeing the files, and would be happy to contribute to firmware (I have wanted to build basically exactly this).

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