Building a 2 circuit system where an 9V RF receiver board activates a relay to drive an input on a NodeMCU WiFi board . Wired it up as per attached sketch. The NodeMCU board was fried after an about 30 seconds of power. My novice brain says the RF board is back feeding 9V through the ground to the WiFi board (maybe via D2) and killing it?
Any suggestions on how to make this work? I know I could run two totally independent power supplies, but not my first choice.
The spec sheet on my NodeMCU board said the Vin pin can take 5-12 VDC
I have read elsewhere to only put 5V at Vin
Per my diagram , will adding a DC-DC converter to get 5VDC at Vin solve my problem and not fry anymore boards?