Movement tracking system
334 USD TECHNICAL TASK
Project: Motion Tracking System (Gym Motion Tracking System)
Stage: Engineering Validation Prototype
1. Device Architecture
1.1 MCU + BLE
- MCU: Nordic nRF52840 or nRF52833
- BLE: 5.0 or higher
- Support for ≥10 simultaneous connections
- MTU ≥ 185 bytes
- Data Length Extension enabled
- RSSI monitoring
Reason for choice: stable BLE stack, low power consumption, OTA DFU support.
2. Sensing
2.1 IMU (mandatory)
- 6-axis IMU:
- Bosch BMI270 or
- TDK InvenSense ICM-42688-P
Requirements:
- ODR: 100–200 Hz
- FIFO buffer used
- Low noise density (≤150 µg/√Hz)
- Hardware timestamping (preferred)
2.2 Magnetometer (optional, for v2)
- I2C connection
- Power-saving disable option
3. Frequency and Data Transmission
3.1 Sampling
- Internal sampling: 200 Hz
- Transmission rate: 50–100 Hz (in batches)
3.2 Packet format (to be agreed with Software)
The packet must contain:
- Timestamp (uint32)
- Acc X,Y,Z (int16)
- Gyro X,Y,Z (int16)
- Battery level
- Device ID
End-to-end latency: ≤ 30 ms
Packet loss: ≤ 1%
4. Power Supply
- Li-Po 300–500 mAh
- Operating time: ≥ 6 hours of active streaming
- Charging: USB-C (5V)
- Charging controller with protection (TP4056 or equivalent)
- Fuel gauge (MAX17048 or equivalent)
Consumption:
- Active streaming: ≤ 15 mA avg
- Sleep mode: ≤ 50 µA
5. PCB and Mechanics
- 4-layer PCB
- Board size: ≤ 35×35 mm
- Antena: integrated PCB antenna (impedance matched)
- Mandatory RF tuning check
Case:
- Impact-resistant ABS or TPU
- Protection: minimum IP54
- Temperature range: 5–40°C
6. Firmware (mandatory requirements)
- FreeRTOS or Nordic SDK
- BLE GATT profile described and documented
- OTA DFU
- Buffering on connection loss
- CRC check of packets
- Unique device ID programmed at manufacturing
7. Testing
The hardware engineer must conduct:
- BLE stability test (10 devices simultaneously)
- Battery discharge profiling
- RF range test (minimum 15–20 m in the hall)
- Drop test (1 m, 5 drops)
- Vibration test
8. Result
Deliver:
- 10 fully functional prototypes
- Gerber files
- Schematic
- BOM
- Firmware source
- BLE API documentation
- Power consumption report
- RF test report
9. Critical for MVP
- Real-time
- Minimal latency
- Stability with 10 sensors
- Readiness for integration with mobile application
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14 days334 USD
744 6 0 14 days334 USD
Hello! I am ready to take on the implementation of this project.
I have extensive experience in developing embedded systems based on Espressif (ESP32), Atmel, and Arduino microcontrollers. Since I actively work with ESP-IDF (FreeRTOS) for complex IoT solutions, working with the Nordic stack (nRF Connect SDK / Zephyr RTOS) will be completely natural and quick for me, as the architectural approaches are identical. In addition to working with frameworks, I have experience writing firmware in bare-metal C (through registers) and assembly language. I work with low-level debugging (GDB), which will ensure strict timing (latency < 30 ms) and optimize sleep modes to achieve target consumption < 50 µA.
I also have practical experience in electronics development: custom interface integrations (I recently gave a presentation on the RS-485 standard, which is in my portfolio) and adapting peripheral modules (LCD, RTC) to specific power requirements. I have worked with KiCad. Additionally, I have practical experience with Li-Ion/Li-Po batteries: creating custom assemblies, testing and profiling their capacity, as well as integrating protection boards and charge controllers, which directly corresponds to your specifications regarding TP4056 and MAX17048.
The specifications mention a frequency of 50–100 Hz for 10 sensors. How critical is the precise time synchronization between all 10 devices? Is it sufficient to simply place a local timestamp before sending, or will it be necessary to implement a time synchronization protocol over BLE from a central gateway? From the packet format, I suspect you need 3D orientation. For that, will primary filtering need to be done on the MCU (like a Kalman filter)?
I propose as the next step to start with the development of a Proof of Concept based on nRF52840 and the BMI270 module. This will allow us to quickly and with minimal costs verify the stability of the BLE connection for 10 devices simultaneously before ordering custom 4-layer PCBs.
…
I look forward to further discussion of the project!!
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