I’m trying to build a simple circuit with a relay controlled by an Arduino that will turn on/off a little LED light string I have that was previously powered by two AA batteries (that would be 3V, according to the diagram on the battery case). I have the circuit wired and the Arduino programmed so that it triggers the relay on every .5 seconds and off every .5 seconds. I would expect the lights to blink with this configuration, but they do nothing.
I have tested quite a few different configurations, I have tested the lights (they work perfectly fine with power directly from my breadboard power supply), and I have tested other known-working devices on the circuit and I have not been able to get anything to work on it. The relay does function as expected — the LED on the PCB blinks on when it is triggered and it does make the clicking noise from the circuit closing — so I figured that it had to be an issue with the load power.
As I mentioned, I’ve got a breadboard power supply attached that should be providing enough power to the circuit to light the lights, and I have tested the lights directly on the power supply and they work. This lead me to think that there must be something wrong with the relay. I tested the output voltage from the relay with a multimeter and I had to turn it all the way to the most sensitive setting to get any sort of reading at all, which turns out to be something in the range of .3 millivolts. Obviously much lower than the expected 5V that should be coming out of there. I checked the resistance through there and it was within expected values.
So my question is, what’s happening here? Why am I not getting power from the relay?
Best Answer
On the relay boards I've seen, the relay contacts connect only to the terminal block on the board - there is no power on the contacts unless you provide it through one of the terminals.
You should connect the positive supply to the "COM" terminal of the terminal block, and your LEDs to either the "NC" or "NO" terminal.