Step-down converter connected to Arduino

I have to connect an Arduino mega to a PLC, and I will need the Arduino to run a sketch once it received a high signal from the Arduino. I am currently testing it on an UNO. I am just a little unsure of how to connect the step-down converter. Here is a link to the converter: https://www.amazon.com/gp/product/B00BWLP88A/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Does anyone have any suggestions?

Are you talking about powering the Arduino or just level shifting a signal? If just a signal use
a resistor divider.

If powering you won't need a 15W converter like that, there are cheaper options, checkout LM2596
converters on eBay for instance.

MarkT:
level shifting a signal? If just a signal use a resistor divider.

Hi MarkT,

I have read in some articles that level shifting by a resistor divider is cheap but dirty. That means the signal will not be good and stable. How do you think?

Depends on the resistor values and the capacitance behind the level shifter.
If you feed the output of the level shifter into a length of twisted/shielded wire, you might end up with a low-pass filter.
Leo..

A resistor divider is cheap and not as dirty as a step-down converter by a long shot for logic signals....