user53009: 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 & 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 & NodeMCU  led are blinking but relay coil does not trip.
Please confirm is my NodeMCU having problems as voltage between vin & GND read 1.9V.
https://drive.google.com/file/d/1Z6jYX4sCLmRxnWbtBYZCNW6LpckokaC9/view?usp=drivesdk


user21371: 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


53009: <p>I have NodeMCU ESP8266N Lolin V3, my 5V relay is powered from Vin of the NodeMCU.
The NodeMCU is powered from 5V USB.</p>

<p>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.
<a href="https://drive.google.com/file/d/1Z6jYX4sCLmRxnWbtBYZCNW6LpckokaC9/view?usp=drivesdk" rel="nofollow noreferrer">https://drive.google.com/file/d/1Z6jYX4sCLmRxnWbtBYZCNW6LpckokaC9/view?usp=drivesdk</a>
<img src="https://i.stack.imgur.com/QIEqV.jpg" alt="enter image description here"></p>
 21371: <p>The voltage on Vin when you power that board thru USB is not relevant ... Vin is not the pin you are looking for</p>

<p>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</p>

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

<p><a href="https://i.stack.imgur.com/0PoF2.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0PoF2.jpg" alt="Lolin v3 pinout"></a></p>

<p>Use this pin to connect to JD-VCC on the relays</p>

<p>I've just now successfully done this with a 4 relay board</p>

<p>I would connect (nodemcu -> relay)</p>

<ul>
<li>3V3 to VCC</li>
<li>VU to JD-VCC</li>
<li>Gnd to Gnd</li>
<li>D<em>n</em> to IN<em>m</em> - i.e. choose a D pin on the NodeMCU and connect to an IN pin on the relay</li>
</ul>
