High Trigger Relay

Hi there,

How can I change the 5V 4 Channel Relay Module (SKU: CE05279) from Low trigger to High trigger?

thanks !

Hi Dylan

There is a Jumper cable on the PCB shown in the picture will select active HIGH/LOW.

thanks for your reply.
From what i understand that jumper is just to use an external power source for the relays? Even if i remove it the relay is still turned on with a digital LOW.
The problem I am having is that when the pin on the arduino is set to low, it activates / changes the state of the relay. Which means as soon as I power the arduino with the particular firmata i’m using, the relay turns on.
I want to be able to power up the arduino and nothing happen until I turn that pin high.
I realise I could change the program to start that pin on high, but I am using firmata to controlling various other things and would be easier at this point to keep HIGH as on, so wondering if there is a simple hardware approach?
many thanks

You could use a MOSFET with the sink connected to the relay pin, the drain to ground and the controller to the gate. I’m fairly sure that would drive the relay pin low when the gate voltage was high.

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OK thanks for your reply and solution . I’m surprised that low trigger seems to be the default behaviour of most relays, it seems to me the opposite would be more useful in most situations, though i’m sure there is a very good reason for it .Cheers

Low triggers seem to be easier to wire up with most microcontrollers, and I think there is another reason but I can’t remember what it is. All the best with the project, let us know how it goes.

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Switching an earth is a very common way to control relays. I makes it really easy to test circuits without worrying about shorting because you just use earth as the control. You will also see that in car relays.

What you could do in your code is start the arduino with the pin as an input, which will make it open circuit or pulled high. When you are ready to control the relay, make it an output and set it low to turn it on, and then high to turn it off.