Relay with TWO Input pins !!!!

jonisonvespaa: this is how to connect to your module, my advice is to have a look at a few relay circuits and learn how they work

gnd to gnd In to your auduino output. Vcc to 5v

Are you not seeing that the OP's module has 2x INs, IN+ and IN- which is why he's asking the question?

May be some testing will be in order....And here I will need your help too. Another mystery (apart from the two IN's) there is a jumper just behind the the FOUR HEADERS it is shortening TWO HEADER Pins. The problem is even the manufacturer of the module is not providing any documentation www.lctech-inc.com

Of course there is the remote possibility that this Module is NOT designed to work with Arduino !!!!!! Anything is possible when you are dealing with Chinese products. The problem is who to talk to ???

I have no idea: it might be worth testing to see if the IN+ isn't just the same as IN on the simpler module?

But it might also be that it needs two inputs together... you said you saw an example using a sensor? Maybe the Arduino could "mimic" that but of course it would need details of what the + and - is still

My educated guess:

GND is obviously ground. Vcc is the power for the relay. IN+ is connected to the anode of the optocoupler (maybe via a resistor, maybe not) IN- is connected to the cathode of the optocoupler. The 2-pin jumper hard-wires the IN- to GND.

We are progressing…The key here is “Optoelectronic coupling Relay” I searched google with arduino and Optoelectronic coupling Relay" and found supplier with that type of relay (ie TWO IN + and - )

and the attachment downloaded from that site, shows clearly the TWO INPUT ( + and -)
See the pdf

In the mean time, I will check the jumper function as you “think” is does…(grounding the IN-)

P.S. This site specializes in Arduino, which means that my module WILL work with arduino…

T-01_Ang.pdf (531 KB)

Good news.... YES the jumper in the back is grounding IN- , so that means I have only ONE Input to try to control with Arduino... I will have a shot and see....

I will be back ;)

Guess what ...It WORKED. The IN+ is connected to digital Pin x The Vcc to Arduino 5V And GND to GND

There is a red led on the module that indicate when the relay is Active, and the sound of clicking made me even happier.

Thank you guys for your support AND patience.. It paid at the end.

If the IN+ is connected direct to the optocoupler you'll be wanting a small resistor (maybe 470?) as if you were connecting to an LED (which in fact you are), or you risk burning out the Arduino's IO pin. OTOH if there is already a resistor in the IN+ line then you're safe.

So the question has to be, why does the one that jonisonhisvespa posted, which is also an optocoupler, have only 1 IN while arishy's has two?

I'm guessing it's so that on the one with 2xINs the grounds don't actually have to be at the same potential? With the jumper in place they are, and only IN+ is needed, but they needn't be?

JimboZA: So the question has to be, why does the one that jonisonhisvespa posted, which is also an optocoupler, have only 1 IN while arishy's has two?

I'm guessing it's so that on the one with 2xINs the grounds don't actually have to be at the same potential? With the jumper in place they are, and only IN+ is needed, but they needn't be?

That is the logical assumption, yes. You can achieve full galvanic isolation between the driving source (arduino) and the relay, as well as the galvanic isolation provided by the relay itself.

I did a short test WITHOUT the resistor that you are suggesting and it worked..Then I had a beer ( Enjoyed every bit of it, I did cheer every one of you !!).

Now, I have the guts to ask you about your last remarks. What you are saying is ; the jumper will help NOT to ground the two parts (The module and Arduino) TOGETHER. If I take the jumper, I will have to connect the two manually.

As for the resistor, how to I check safely that I do not need a resistance ( No documentation as you know)

To check the presence of a resistor just either check the resistance between IN+ and the pin it connects to on the optocoupler (black chip) - just buzz it through with a DMM to find the right pin. You can also do it visually by following the traces around from the IN+ pin.

The optocoupler is basically an LED on one side and a transistor on the other. You are controlling the LED - making it light up. Connecting the two pins of an LED to an Arduino, you connect the anode (+) to the output pin (through a resistor) and the cathode (-) to ground. The LED lighting up switches the transistor on and off. That transistor then switches the relay on or off. The relay and transistor aren't connected to the LED at all (called "galvanic isolation"), so they do not need to share a ground. You can think of the transistor as a pushbutton and the LED as a finger. Your finger doesn't form part of the circuit at all, but it affects the circuit it's pressing.

So you can remove the jumper and connect the IN+ to the IO pin (as it is now) and the IN- to the ground on the Arduino. The Vcc and GND pins on the relay module can then be connected to a completely different power supply, like a battery, which doesn't have a "ground" as such, and isn't connected to the arduino in any way at all. And it works - in the same way that the light-switch works even though you're not plugged into the mains.

Thank you majenko.
I will have another beer, this one is for you…Cheers