HB100 is a doppler radar module which can be bought on eBay for about $5.
The board on the back is a homemade preamplifier (stock datasheet schematic), because the output signal from the module has amplitude of only a few uV.
Arduino Nano runs a slightly modified LCD example sketch from the FreqMeasure library.
Source code and hardware design files are on my GitHub: [ Ссылка ]

You can buy complete modules with radar + amplifier here: [ Ссылка ]
FreqMeasure Library: [ Ссылка ]

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