C4001 mmWave sensor – target range stuck at 2.84 m

Hi everyone,

I recently bought a C4001 mmWave sensor and I’m having an issue with the reported distance value.

After properly wiring and powering the sensor, I tested both I2C and UART communication using the example code from the DFRobot library. However, the target range is always fixed at 2.84 m, regardless of the actual distance to the target. The same thing also happens with the target number: even when there is nothing in front of the sensor, it always reports 1.

Here’s an example of the output I’m consistently getting:

target number = 1
target speed  = 1.97 m/s
target range  = 2.84 m
target energy = 0

target number = 1
target speed  = 2.15 m/s
target range  = 2.84 m
target energy = 0

Observations:

Target number is always 1

Target speed changes randomly (0–2 m/s)

Target range is always exactly 2.84 m

Target energy is always 0

Same behavior over both I2C and UART

Issue persists across power cycles

I expected the range value to change when moving closer to or farther from the sensor, but it never does.

Has anyone experienced something similar with the C4001?
Is 2.84 m some kind of default or initialization value?

Any help would be greatly appreciated.

Thanks in advance!