Is my relay working?

I want to control a lamp with my Arduino - usual stuff, I’ll have a PIR sensor and light sensor and it will come on if it is dark and someone passes it.

So I bought one of these relays.

To test it, I hooked up VCC to 5v on the Arduino, GND to Ground on the Arduino, and IN to Pin 2 on the Arduino.

I then used a simple sketch to switch Pin 2 Output between HIGH and LOW with 2 second intervals.

My expectation is that I would hear the relay click, but nothing. I can see the DS2 lamp on the relay light up and switch off every couple of seconds.

Do I need to put an actual load on the other side before the relay will click?

I know there is an optocoupler between both sides, so if I put my multimeter probe between common and NO or NC on the relay should I expect to see some voltage?

I’d rather not put the 120v through it until I know it is working.

The best way to see is to use a LED and R through the relay contacts. It may simply be a quiet operator.

I also bring to your attention that the relay connections on the board can be contacted when handling the board. This can be very dangerous. Make sure you treat the board as live and protect it as such.

Weedpharma

Do I need to put an actual load on the other side before the relay will click?

No. You should be able to hear a faint click with no connections made to the contacts.

I know there is an optocoupler between both sides, so if I put my multimeter probe between common and NO or NC on the relay should I expect to see some voltage?

No, the contacts are dry (like a switch that hasn't been connected to anything). You could switch the multimeter to continuity check to hear a beep, or use resistance measurement to see a change in reading. Measure from COM (middle terminal) to NO or NC terminal.

Try this to test (1 sec ON, 1 sec OFF):

#define RELAY1 2

void setup()
{
  pinMode(RELAY1, OUTPUT);
}

void loop()
{
  digitalWrite(RELAY1, LOW);    // Turns ON Relay 1
  delay(1000);                  // Wait 1 second
  digitalWrite(RELAY1, HIGH);   // Turns OFF Relay 1
  delay(1000);                  // Wait 1 second
}

Note: It will take about 100 ma to operate this relay board. Does your Arduino board have enough current available @ 5V? Also note that if you're powering your Arduino with 12V, you'll have much less current available at 5V than if you power your Arduino with 7-9V.