I have a NodeMCU project (8266 variety) for Apple HomeKit that allows me to control 4 relays with manual switches, Siri voice control, and the Apple Home app manually via my iPad and iPhone. This all works great and I can turn things on and off using HomeKit.
The project box is powered by a FULARR MP1584EN DC to DC Buck Converter (4.5-28V In to 0.8-20V Out Step-Down Voltage Regulator) that supplies regulated 5V power to the NodeMCU and the relays (and a few status LEDs). This all runs off a 12V DC nominal solar/LiFePO4 battery system in my off grid cabin.
But, set up and coding the NodeMCU becomes an issue after I solder all the components together as the project has two power input sources; the buck converter attached to VIN and the USB micro port. When I want to update code I need to disconnect the project box from the 12V DC power source and power the whole thing via the USB micro port so I can use the Arduino IDE and watch the serial terminal.
What I want to do is build a USB cable that doesn’t supply power at all from my laptop, but simply provides serial communications, which would allow the project box to be powered via the VIN port but still allow me to program and monitor the terminal output using the USB port. I believe it’s risky (or flat-out dangerous) to have NodeMCU connected to power using the VIN pin and USB port simultaneously, even if there is a diode intended to prevent power feedback.
I’ve searched the internet for feedback on if the “no power” USB cable would work, and as usual, find answers that say “sure, it will work fine” and “no way that will work”. I’ve looked at the schematics for the NodeMCU ( HiLetgo ESP8266 NodeMCU CP2102 ESP-12E Dev Board) and it seems like it would work, but I’m no schematic wiz so I thought I’d ask for feedback here.