LD2410 radar sensors

As I worry about safety around my rover I've been looking for a way to detect people that doesn't rely on anything complicated like AI image analysis and can be done with a simple cheap sensor.

By chance, Andreas Spiess did a brief review of the new Hi-Link LD2410 24Ghz radar sensors, which are designed for presence detection.

They look promising and aren't expensive, so I bought a few along with the dedicated UART breakout board made for them.

My little bit of testing suggests they're really quite good at detecting people within a few metres, whether they are moving or not and people are rarely completely still. At close range it can tell if you're breathing.

While you can just connect one of the pins to a GPIO to signal presence they use a serial protocol for configuration and more detailed readings. However as they are comparatively new devices there wasn't a library for this.

Between reading the work somebody has started on integrating them into ESPHome and the slightly confusing manufacturers datasheet I've cooked up an Arduino Library and submitted it to the Library Manager. I hope people find it useful.

Now I need to make some breakouts for them, they use 1.27mm headers, and attach them to my rover.

Hoverboard motor powered rover: Part 5

I've slowly been chipping away at adding sensors to the rover and it's at a point where I really need to dig deep into RobotOS (ROS) and start on tying it all together.

The Wyse 5060 thin client has been screwed to an old VESA TV bracket, which works OK but tends to come loose under vibration. Given I primarily want to make the rover drive around outdoors this urgently needs fixing.

The Kinect has been cut down, using information from this blog post so it can be screwed directly to the top deck and this works really well.

I threw a bit of effort at software and the sonar range finders are now an I2C peripheral of the Wemos D1 Mini that talks to the remote control and sends commands to the motor controllers. I also found an old MPU6050 accelerometer and a nice tilt compensated compass to give reliable orientation information put these on the I2C bus.

The 5060's original SSD was too small to be practical, being only 8GB. I happened to have a larger one in an unused machine and bought a cheap adaptor to make it physically fit, so the onboard computer's now running a full copy of Ubuntu and it's possible to remote desktop into it and test the Kinect 'live'. A couple of USB WiFi dongles, while not ideal connect it to my home network indoors and provide a 'hotspot' for working on it elsewhere.

With the D1 Mini connected over USB to the the 5060 it should be possible to use rosserial to pass all I2C connected sensor information and detail from the motor controllers sensors back to ROS, while accepting 'twist' commands to move. I do vaguely wonder if I should move to an ESP32 though, as the D1 mini is rather busy with synchronous tasks that could do with being done on a second core but more importantly having hardware UARTs to talk to the motor controllers would be far better than the software serial library I'm using.

I've also plugged a USB GPS dongle I had in my box of project bits into a spare port.

Which means I've close to a full 'sensor suite' for a basic rover. The Kinect won't work outdoors and the GPS won't work indoors, so I still need to come up with something to cover these complementary gaps and do a load of work on sensor fusion, but learning about this topic is the whole point of this project.

I see LIDAR and custom made wheel tick sensors built into the hoverboard motors in my future. The former will give some outdoor obstacle location for mapping and the latter help with dead reckoning indoors. Dead reckoning is not going to work on loose surfaces, but will do OK on nice indoor flat floors and be backed up by the Kinect.

As this very much got me to a solid milestone on the rover, I've christened it with a name, 'Crufty' as it's made from 'maker cruft' and intend to write up/open source large chunks of it on Github.

It was also an opportunity for a presentation at my Raspberry Pi meetup despite the total lack of Raspberry Pis in the build.