12 V relay buzzing/fast clicking sound when getting signal from Arduino UNO

Question

I'm new to electronics but I decided I want to try and build a simple circuit to control with my Adruino UNO R3.

I want to make a relay switch on and off programmatically with my UNO.

Here is my current code:

    #define RELAY_PIN 2
    
    void setup() {
      pinMode(RELAY_PIN, OUTPUT);
    }
    
    void loop() {
      digitalWrite(RELAY_PIN, LOW);
      delay(2000);
      digitalWrite(RELAY_PIN, HIGH);
      delay(2000);
    }

Here is the diagram of my current circuit:

The relay I'm using is a 12 V low level trigger relay (in diagram.)

The problem is when the IN1 wire is connected to pin 2 on the UNO, the relay buzzes consistently and doesn't open/close the circuit, but when I take the IN1 wire and put it into 12V- on the power supply, the relay opens/closes.

I watched a YouTube video where a BC547 transistor was used. I tried it (UNO D2 to base, IN1 to emitter) and no success as well.

How do I get the relay to work correctly?

Answer 1

1. You need a ground wire from the Arduino to the relay module. (This has already been mentioned and didn't completely fix the problem.)
2. Power the relay module from 5V instead of 12V. The relay have a rated coil voltage of 5V, not 12V and there doesn't appear to be a voltage regulator on the board.

This is how you should wire it using a power supply:

^{simulate this circuit – Schematic created using CircuitLab}

You should be able to wire it this way:

^{simulate this circuit}

That should work if the relay module only requires 5V as I suspect.

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If you are really using the pictured power supply, you need to be very careful around it. There are exposed screw terminals with 220VAC on them. Touching those screw terminals could kill you.

Answer 2

You need to connect a ground wire from the Arduino to the ground of the relay board in addition to the IN1 wire you already have connected such that they are working from a common ground potential.