Relay Board jumper cap.

I am looking to give a relay board an independant power supply to protect the arduino uno board.
i have a 5v regulated transformer.
I know i remove the jumper cap and attach 5v supply to the JDVcc pin.
It then looks like I need to attach the ground to the ground pin.
However the transformer has positive neutral and earth outlet terminals.
Postive is the 5v supply but which is the ground the neutral or the earth.

Apologies if this is basic stuff but bear with me.


Please don't confuse the term transformer and power supply.

The power supply has "isolated" + and - outputs, so you can configure either as "ground" by connecting the power terminal to the supply ground terminal.

For your project, connect the - to the ground terminal on your supply, then connect the ground terminal to the Arduino ground.


Thanks for response Paul.
Just to be clear. + positive 5v . -neutral to gnd pin on relay board and earth to ground pin on arduino board.


Thanks for response Paul.
Just to be clear. + positive 5v . -neutral to gnd pin on relay board and earth to ground pin on arduino board.



OK, we are risking confusion here.

A power supply with positive (red), negative (black) and ground (green or maybe yellow) terminals is a bench power supply.

Like this:

If using one of these, you connect the positive and negative, but do not connect the ground terminal to your circuit; it is only for safety grounding; not relevant in your application.

When using one of the active-low opto-isolated relay modules with a terminal marked "JD-VCC" and a separate power supply for the relays, you remove the link, connect the "JD-VCC" and "GND" terminals to the relay power supply using a paired cable, connect the "IN" terminal(s) and "VCC" terminals to the Arduino control pin(s) and "5V" but do not connect "GND" to the Arduino.

Hi Paul
Thanks makes more sense now.
A purely mechanical background and age are working against me your patience is much appreciated.
I think I have attached the power supply I will be using Terry.

That looks a trifle over-rated for a relay board - in fact, seriously over-rated (in terms of available current)! :astonished: It will of course work.

The ground terminal is for the required ground wire in the power cable with a three pin plug, not for your circuit. The annotation tells you that while "Live" and "Neutral" are intended to match the terminals in the power plug, it is not critical if they are exchanged. Only if you add a power switch should you be careful to ensure it is in the "Live" wire from the plug.

The power supply is intended to provide considerable current if required, that is why it provides two negative and two positive terminals, but the two of each are exactly the same terminal. You only need one of each.

There is however a further discussion here.

If that power supply is set to 5 V, it will be perfectly adequate to power the relay board and also the Arduino. It is not really a matter of "safety" for the Arduino; the problem with relay boards is generating impulses which interfere with the microprocessor operation.

You can use that supply to power the Arduino and to do so, you would take a twin cable (lightweight "figure eight") from one positive and one negative to the relay board, and another twin cable from the other positive and negative to the Arduino. That separate cabling provides isolation between the two; the current drawn from one device cannot affect the other because the power supply maintains the voltage at its terminals accurately.

The only "danger" to the Arduino is that if a short circuit occurs, the power supply might provide sufficient current to vaporise the offending component and could damage the wiring if it is too lightweight. But you will obviously ensure that no short circuit occurs. :grinning:

Hi Paul thanks for your valued advice hope I can return favour someday.