Below are the reference documents I consulted:

Attachment: Rd-03 Serial Communication Protocol Rd-03_v1.0.0.pdf

Attachment: Rd-03_V2 Serial Communication Protocol V1.0.0.pdf

Attachment: HLK-LD2402 User Manual V1.08.pdf

1. Comparison of PC Software (Upper Computer)

There is little difference among the three modules in terms of their upper computer (PC-side) control software. Both the Rd-03_V2 and LD2402 offer features such as automatic threshold generation, environmental interference detection, and power interference detection.

However, the Rd-03_V1 lacks a dedicated micro-motion detection section. Although its documentation references “threshold maintenance,” it does not explicitly separate micro-motion detection from the general detection range. Overall, the functionalities are largely similar—right down to the occasional connection lag that occurs.

Based on experience, such lag is typically caused by a blocking receiving mechanism. It would be interesting to see whether the manufacturer might consider optimizing this part of the software in future versions.

2. Detection Range Comparison

From V1 to V2, the Rd-03 radar module introduces static presence detection while expanding the detection range for both micro-motion and motion modes.

However, one may notice that the micro-motion range in V1 appears nearly identical to the static detection range in V2, suggesting they might share the same underlying criteria.

Additionally, it’s worth mentioning that the range illustration in the V2 manual seems to have been copied from another source—complete with a visible PDF editing box.

As for the LD2402, its performance parameters are nearly the same as those of the Rd-03_V2, making it a good reference for comparative evaluation.

Below is a diagram showing the two typical installation methods. Since all three radar modules share similar mounting structures, only one example image is provided.

3. Command Comparison and Hidden Instructions

This section focuses on the most critical aspect—the command set comparison, revealing the meaning behind several hidden instructions.

Recall that in the module specifications, all three radar systems are based on ICLEGEND Micro’s S1KM0000 chip. According to the datasheet, this chip provides standard communication interfaces such as UART, I²C, and SPI.

Upon reviewing the circuit schematic, it became evident that the exposed connections correspond to the UART and SPI ports. This strongly suggests that the on-board MCU mainly functions as a data forwarding interface, while the core communication protocol is fundamentally defined by the S1KM0000 itself.  

Firmware Version Query

This instruction appears on page 13 of the LD2402 user manual.

Serial Number Retrieval

The previously unknown command turns out to be for reading the module serial number, as specified on page 15 of the LD2402 manual.

parameter read instruction, which I initially overlooked. Both the command and response values are multiplied by a constant N, as mentioned in the manual (though this could be described in more detail).

Debug Mode

Finally, the mysterious “unknown working mode” from the Rd-03_V2 manual corresponds to the debug mode described in Section 2.2.5 of the Rd-03_V1 manual.

Conclusion

All previously unidentified commands have now been clarified. They are simply legacy commands retained from earlier firmware versions but omitted from the latest documentation.

This analysis should help developers and users gain a clearer understanding of the upper computer data and the overall communication behavior of the Rd-03 series radar modules.