Preamble: I have little knowledge of electronics in detail, but I know how to solder, have a working brain and am fearless :)
There are many low-cost Microwave Radar Switch PCBs out there (very popular is the RCWL-0516). I just came across the rather unknown XZG-LDK-6: The neat feature of this board is that it works on the power it is switching (as long as it is between 3.3 and 12 volts). In other words: It simply sits between the PSU and whatever device (lamp, motor etc.) you intend to power.
In my case I want to power (5v USB) a wall-mounted Android tablet, which I use as Smarthome controller. The idea is that the tablet is sleeping/in screen-saving mode, but immediately wakes up (= shows the control panel) as motion gets detected: disconnecting the USB power from the tablet for a moment does the job.
The catch is that I need the Microwave Radar Switch to operate in reverse mode: When motion gets detected it should NOT close the circuit, but open it. So constant power to the tablet with no motion, no power with motion detection. As if one would unplug and replug the USB plug on the tablet.
Unfortunately I can't find a schematic of the XZG-LDK-6 on the web and it seems impossible to figure out the manufacturer (there are trading companies on Alibaba and AliExpress, but no manufacturer).
When looking closely, one can see that the B1261 transistor (Q2) seems to be directly providing the output power.
My question is: How to revert the NO (normal open) to NC (normal closed) behavior? With a relay this would be easy, but how do I do this with this transistor? Are there NC and NO types of transistors? Do I simply rewire the existing B1261 transistor?
