[SOLVED]Relay board to control light bulb

Tonyr1084

Joined Sep 24, 2015
7,905
Here's my take on the pictures and schematics. Keep in mind part of this is a guess. Others may likely have a better idea what's going on. Also, NO's and NC's may be reversed but it looks fairly confident the common (C) is correct. But then again, maybe not.

1604268624517.png
 

jpanhalt

Joined Jan 18, 2008
11,087
Based on the drawing you post in #24, why do you expect a voltage between NC and COM?

Assuming the positive terminal of the 5V DC is connected to NO and its negative pole to the same ground to which the LED is connected, then:
1) There should be voltage between NC and NO when the relay is NOT energized.
2) There should be voltage between COM and NO when the relay is NOT energized.
3) When the relay is energized, there should be no voltage (or very low due to contact resistance) between NO and COM.
4) When the relay is energized, there should be no voltage between NC and anything. NC is floating.
 
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