OBTW this is following the wiring for the "IoT Smart Garden Setup with Nano RP2040 Connect" project. Note - power is disconnected before making any changes.
Results:
- Remove the Nano Connect from the Screw adapter, connect it via its USB connection to the laptop using a data synching USB cable and it operates as expected (i.e. able to see it on the Windows Device Manager, and via the "Select Other Boards and Port" in the IDE, and able to upload sketches).
- Remove all connections to the Screw adapter, insert the Nano and it operates as expected.
- Connect a USB 5V power supply to the Screw adapter (Vin and GND), then plug it into a brick. The Nano operates as expected and voltages are good.
- Connect a soil moisture sensor to an analog pin set for pinmode INPUT, Vin and GND. Upload and run a sketch that successfully reads the analog pin.
- Connect a relay to the V3.3 pin, GND and a digital pin set for pinmode OUTPUT, upload a simple sketch to toggle the relay, and the Nano and relay operate as expected.
- Connect power lead to a small 5V pump to one terminal on the relay and Vin to the other terminal and problem reappears (i.e. serial connection is lost and relay cycles rapidly).
Tracking down a schematic for the relay now. Maybe it matters which terminal is used, or 3.3V is insufficient to drive the relay. We'll see.