Back on 24 GHz with Hi-Link HLK-LD1115H

General info: I am discussing the (ab)use of these radar modules as amateur radio transceiver on 24 GHz, not their motion/presence sensing application.

 

After a relatively successful contact with CDM-324 free running modules over a 100 metres distance, my friend and "wideband FM gigahertz partner" Mauro started looking for better alternatives, but still cheap.

RF side of HLK-LD1115H

There's a nice writeup of the current (2022-2023) offering of these modules by Bertnik at https://revspace.nl/FMCWRadar .

Mauro chose the Hi-Link HLK (probably www.hlktech.net) HLK-LD1115H module on aliXss that costs about 5€/USD each. Apparently those use a clone/copy/emulation of an Infineon BGT24 chip, with the same features but less output power: the SGR SRK1101A. They have on-chip temperature sensor for compensation, they are tunable (300-600 MHz/V), they include a prescaler with /16 or /8192 output so you can even build a PLL control around them.

Cool, aren't they. Well, they are as cool as tiny: there is almost no way to solder directly on their pins as the spacing for the 16QFN is 0.5 mm, so we needed a module that routes on the PCB as many pins (= functions) as possible.

I bought a couple of HLK-LD1115H to play with. Why two? To have a ready backup if I break one module and, if everything goes well, to have a receiving or transmitting counterpart as Mauro doesn't live exactly next door.

I did the usual overimposed front+back picture to try to reverse parts of the schematic diagram, but being a 4-layer board some traces are not visible and vias just "disappear".

Plan B, then! Under the most powerful lens I own and with the help of a continuity tester, search where each pin goes by poking pads around the PCB. The process is not complete and the result will be documented in a future post.

Logic side of HLK-LD1115H.

You can click on both pictures to get a larger version. The larger TSSOP chip is an STM32F030F4P6 microcontroller while the smaller is a dual op-amp RS622 with 7 MHz GBW. One top-right corner is a 3.0V regulator LN30.