"Inside a $1 radar motion sensor" (2024), 100 comments, https://news.ycombinator.com/item?id=40834349
"WhoFi: Deep Person Re-Identification via Wi-Fi Channel Signal Encoding" (2025), https://news.ycombinator.com/item?id=44685869
But I guess you should be careful if you are trying to modify this into an RF pulse welder and someone left their cutting torch gas cylinders venting nearby. </s>
When a car approaches from behind you get a visualisation on the bike computer showing you how far away the car is and an audio alert. If the car is approaching fast you get a different audio alert and the light flashes differently to warn the approaching car. It also detects up to three cars.
There might be improvements to be had but the implementation is pretty solid.
There's one feature they all miss. They only measure relative velocity to You. That's definitely better than nothing, but in my experience the most dangerous drivers aren't necessarily the fastest ones, but those who pass too closely. So, something like "angle of approach" measurement would be a feature I'd personally be willing to switch my Varia for something else.
Also, 15usd is not cheap for this kind of chip. You can buy a full wifi 7 rf/modem or a 4 core arm64 soc with this kind of money.
This is a phased array device. Angular resolution 20 degrees, range resolution 1 meter. It's not a Doppler radar, so it can detect fixed objects. So if you're using it for people detection, you have to tell it where the fixed objects are. A ceiling mounted unit will see the floor. OK for people counting and such. Range is only 10 meters.
If you just want a motion detector to turn on a light, and IR isn't working for you, there are cheaper microwave detectors.
They offer 50GHz, 10GHz, 24GHz and 60GHz FMCW radar module boards for 10-30€ which are easy to reverse engineer on firmware and PCB level.
A lot of them are CW radars, a few FMCW and they also use the Infineon 60GHz radar chips. Very unusual for Infineon: with all tools and datasheets available without signing a NDA. Down to the register level.
There's an interesting Chinese company around (ICLink with their ICL1122/ICL1112) which offer highly integrated radar ICs. They can spit out raw ADC measurements of their downmixed baseband using Quad SPI at 20 or 40MHz when switching on their debug mode. Price range: ~10€. But datasheets are difficult to find. Example board: LD2410S.
The analog ones are easy to play with. You just need a DAC to drive their VCO and then can sample the I/Q pins with an ADC. That how a lot of the 24GHz modules (like the LD1125H) work.
Unfortunately even just pointed straight at me with no obstructions and nobody else in the room the data was more or less random noise...
I wonder if now (after few more years of development, more reputable manufacturer and more money) it is worth trying again?
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