Hello,
would anybody happen to know if there is a way to control an Arduino Leonardo or UNO via USB with a simple program or executable file.
The thing is that we have a few aerosol evacuation systems controlled with Arduinos which work great with a push button however we would like to integrate it more. So what I'm looking for is a sort of digital button on a PC that will trigger the script that is already on the Arduino itself so that we can combine that with a script that triggers the button and a few other things that are not related to the Arduino.
I know it may be a stupid question but I couldn't find an answer 
You need to use Serial communication to send instructions or orders to arduino. This can be done using USB.
You need to search in Serial library examples and tutorials.
Another option might be to use Firmata if you want to write your own PC controller as the Arduino IDE includes firmata libraries.
You can also write a PC program in almost any language you want to send and receive data to/from an Arduino. Python is popular. I use JRuby. For most programming languages the Arduino is treated as a serial connection over a (virtual) COM port.
...R
Thank you for your assistance, I will definitely look into these. I'm sure I can make something work 