Connect both GNDs together via the module’s GND pins – they are internally connected, but still wire both for low impedance.
Bridging the Gap: A Guide to the HW-044 RS232-to-TTL Converter hw-044 datasheet
// ... pin definitions and setup as before ... Connect both GNDs together via the module’s GND
At first glance, it looks like a simple push-button or limit switch module. But if you just treat it as "button in/button out," you are missing half the story. Today, we are going to pull the actual HW-044 datasheet apart and look at the circuit, the logic, and why this module behaves differently than a raw mechanical switch. hw-044 datasheet