SparkAltBatteryBoard

A custom research-oriented battery interface and telemetry board for the DJI Spark platform, built around a standard 3S LiPo battery pack instead of the discontinued, hard-to-find OEM Smart Battery.

This project documents a reverse-engineered I2C/SMBus smart-battery communication interface, originally developed to study how the DJI Spark flight controller communicates with its battery pack. The board sits between a standard 3S pack and the drone, reads the real cell voltages and current, and reproduces that communication interface.

How it works

1. The original DJI Spark Smart Battery was disassembled and its I2C/SMBus traffic with the flight controller was captured with a Saleae Logic Analyzer.
2. That traffic was decoded to recover the SBS + DJI-proprietary command set (auth handshake, cell voltages, PEC/CRC-8, etc.) — see Docs/I2C_BMS_PROTOCOL.md.
3. A custom PCB replicates the OEM battery's form factor and connector, with resistor dividers for per-cell voltage sensing and an INA199 current shunt amplifier.
4. An ATmega328P on the board reproduces the Smart Battery communication interface over I2C in real time — computing PEC on the fly and clock-stretching where needed. See Firmware/README.md for the full protocol implementation.

Repository structure

Hardware

Top	Bottom	Layout

• MCU: ATmega328P — chosen specifically because its hardware TWI peripheral supports I2C clock stretching reliably, which the DJI FC's polling requires (see Firmware/README.md for why an ESP32 doesn't work here).
• Sensing: 3-way resistor divider network for per-cell voltage taps, INA199 shunt amplifier for pack current.
• Full schematic: Docs/SparkAltBatteryBoardV1.pdf
• Fabrication outputs: BOM · Gerbers
• Battery mount: Mechanical/batterymount.stp

PCB Design / Manufacturing Notes

The PCB revision was prepared as a manufacturing-oriented KiCad project, not only as a proof-of-concept schematic.

Design considerations include:

• Hierarchical schematic structure
• Separated MCU, power, sensing, and connector blocks
• 3.3 V I2C/SMBus logic interface
• ADC-scaled cell-voltage sensing inputs
• RC filtering on analog measurement lines
• INA199 high-side current-sense frontend
• Kelvin-style shunt measurement routing approach
• Buck-regulated 3.3 V system rail
• I2C pull-up resistors
• ESD/TVS protection on external communication lines
• AVR ICSP programming/debug header
• Wide copper routing/polygon strategy for battery current path
• Manufacturing outputs prepared: BOM and Gerber package

Firmware

PlatformIO project targeting the ATmega328P (Arduino Uno/Nano pinout). Handles the I2C slave logic, ADC reads, CRC-8 PEC calculation, and all SBS/DJI command responses.

pio run -e uno
pio run -e uno -t upload

Full pin map, supported command table, and known limitations: Firmware/README.md.

Protocol reverse engineering

The raw logic analyzer captures used to decode the protocol are included for reference:

• Docs/sniffedsession2.csv
• Docs/sniffedsession3.csv
• Full write-up: Docs/I2C_BMS_PROTOCOL.md

Legacy Prototype Flight Test

The video below shows an earlier prototype tested around 4 years ago. It does not represent a flight test of the redesigned PCB revision in this repository.

Disclaimer

This is a hobbyist reverse-engineering project, shared for educational purposes. Flying with a modified battery/BMS is at your own risk — verify cell voltages, current limits, and wiring yourself before flight. Not affiliated with or endorsed by DJI.

The original prototype was flight-tested in the past. The redesigned PCB revision in this repository has not yet been flight-tested because the original test drone was later damaged in a crash.

License

Source-available for personal, educational, and research use. Commercial use is not permitted without written permission. See LICENSE (MIT with Commons Clause).