Hello, I have a problem with the control of a relay (Arduino UNO): if I give the relay 5V it triggers fine, but the Arduino only gives it 4.6V and it does not activate.
The Arduino pin gives me 4.9V when I measure the voltage, but when it is connected to the relay it drops the voltage, I don't know why.
The relay is like this : Modulo Rele 5V 10A de 1 Canal Disparo Bajo Alto Para Arduino ARM PIC AVR DSP PIC 8433799097968 | eBay
I appreciate your help.
Hmmm, seems a bit strange.
It would help if you added some pictures of your circuit.
Are you sure you connected 5v and GND properly to the relay? The Relay should take in 5v, GND, and the Signal line.
Do you have another Arduino that you could try to use?
Noah
Show us a good schematic of your circuit.
Show us a good image of your ‘actual’ wiring.
Give links to components.
Posting images:
https://forum.arduino.cc/index.php?topic=519037.0
What’s written on the top of the relay.
Don't try driving relays directly, the output of the Uno will not support it. Use a buffer transistor.
AJLElectronics:
Don't try driving relays directly, the output of the Uno will not support it. Use a buffer transistor.
Hmmm. Did you actually look at the item the OP cited?
To operate this relay you need to connect:
DC+ to your 5V supply, best not to connect it through the Uno
DC- to you 5v supply common or negative.
In to the Uno pin you are trying to control it with.
And the LED on the relay module should be illuminated regardless of if you are trying to turn the relay on or not.
Also the jumper should be such that the 5V mentioned above is connected to the input (coil) of the relay.
Paul__B:
Hmmm. Did you actually look at the item the OP cited?
Clearly not. I didn't even see the image!
eBay is playing silly beggars - blocking their images. They clearly do not want anyone referring business to them. 
If you right-click and "View Image" it will show.
I also corrected and anglicised the product link above. 
Hello.
forgive my mistake, the setup () I forgot to put this
pinMode (relePin, OUTPUT);
With that, everything works ok.
I appreciate your attention.
Thank you for updating your post with the solution.
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