Difference between these two relays (D1 Mini Relay Shield and Single 5V Relay) I've setup my NodeMCU v3 with this relay and I got this:


When using 3V to power the relay, I can hear coil when I turn on the board and I can only turn it on once. Then I can no longer hear the coil, but LED turns on and off.
When using VU pin (5V) to power the relay, I get the same coil sounds (when turning on board and on first toggle), then nothing. But the LED stays on, just slightly dims itself when turning on. Barely noticeable.


Alright, but I had a D1 Mini relay shield* laying around and I decided to give it a try. And it worked when powering the shield with VU pin (5V). 

So my question is what is the difference? Does the D1 Mini Relay Shield have a transistor to pull up pin voltage from 3V to 5V and the other relay doesn't? If I had a logic level converter 3V-5V between the NodeMCU GPIO and the relay IN, would it work? 

Thanks in advance. 

*must say mine is a clone, but it works
Ok, so:


I've bought a logic level converter.
Bought another relay.


Now to the results:


With the first relay, no joy with 5v or 3v in any combination (3v on VCC / 3v on IN; 5v VCC / 5V IN; 3V VCC / 5V IN; 5v VCC / 3V IN)
With the second relay (the new one), funny enough.. Didn't work with 5V on VCC and 5V on input. But it did work with 3v on both of them.


I measured every output voltage to make sure everything was working fine and it wasn't a problem with power supply.

I guess it should work with 5v...? Right?

Anyway, it was indeed a faulty relay. And 3V on VCC and Input is what worked for me, even though it is a 5V relay. Thank you all for the assistance.