What is the voltage between Vin & GND? I have NodeMCU ESP8266N Lolin V3, my 5V relay is powered from Vin of the NodeMCU.
The NodeMCU is powered from 5V USB.

My difficulty is when I measure voltage between Vin &amp; GND, it is of 1.9V, but supposed to be around 5V as it is directly attached with usb 5V supply. Actually my relay is not working with the power tapped from Vin, but relay's led &amp; NodeMCU  led are blinking but relay coil does not trip.
Please confirm is my NodeMCU having problems as voltage between vin &amp; GND read 1.9V.
https://drive.google.com/file/d/1Z6jYX4sCLmRxnWbtBYZCNW6LpckokaC9/view?usp=drivesdk
The voltage on Vin when you power that board thru USB is not relevant ... Vin is not the pin you are looking for

You clearly have a Lolin NodeMCU (V3) board - the existence of Gnd and VU (looks like VV in your picture!!) between A0 and S3 pins indicates that

In documentaion easily found by searching for Lolin V3 pinout - VU is described a USB power output



Use this pin to connect to JD-VCC on the relays

I've just now successfully done this with a 4 relay board

I would connect (nodemcu -> relay)


3V3 to VCC
VU to JD-VCC
Gnd to Gnd
Dn to INm - i.e. choose a D pin on the NodeMCU and connect to an IN pin on the relay