DFROBOT Gravity: mmWave C4001 24GHz Human Presence Detection Sensor (12 Meters, I2C & UART)

Really sensitive, I made a diy burglar alarm

I integrated this into a LoRa mesh node in my ChatterBox cluster so I could have an off-grid mesh proximity sensor, and it's been working reliably for months now. This is very sensitive. I still don't quite understand the detection area/angle, because it senses motion when I am nearby but seemingly out of its detection range. Thats not really a negative for my purposes, but it might be for yours. I am only using it for a motion/no motion check. The API offers the ability to measure speed and other things. I played with that for a while, just for curiosity, and never got that working consistently. The basic motion sensing does work consistently. The board does use a decent amount of power, so it will use up your battery fairly quickly if you don't have a decent sized one. It gets just a little warm too, nowhere near hot, just a little warm. I leave it running 24/7 and have had no issues from it. For the price and ease of use, I'd say it's quite a good value.

The sensor works pretty good if you want it to just be a static presence sensor. That of course is only if you drain 10+ hours of your life trying to get the code / communication working so you can configure it. The new protocol document on DFRobot's website helped with being able to actually talk to this thing but after 5 more hours of messing with it I have discovered that in "speedMode" the sensor is basically useless. The noise floor is so high that you cannot reliably detect anything. I have tried it indoors and outdoors with pretty much every possible configuration. I can place the sensor still on my desk and leave the room and it will still detect something every few seconds or so. I think this is due to speed modes reset cycles ( undocumented ) I can also turn the sensitivity to the max and sit right and front of it in speed mode and it will drop my presence every 2 seconds or so. TLDR: This thing is useless in speed mode and works fine in presence mode. Configuring it required 10+ hours of your time to figure out all the of errors in their SDK, documentation, and code. If enough people still want to give it a shot, I can put my code on github as i now have a reliable debug tool that actually works unlike DFRobots.

The unit I got is defective and ended up shorting two of my micro controllers when wiring it in the recommended way on their website. DFRobot also deleted their C4001 library for Arduino including the GitHub project, so even if my unit was working you now have to manually figure out the data input.