Connecting Arduino output to parallel breakout board input - resistor required?

Hi all,

I'm very new to Arduino but I'm using one (Mega 2560) as the "brains" in a CNC machine that I'm trying to build.

I have a "breakout board" connected to a PC parallel port. It allows me to output/input to the PC to run the Stepper motor drivers etc.

There's inputs for "homing" the axis of the CNC machine.

The breakout board is 5V so I wanted to know if I could just link the GND on the breakout board with the GND on the Arduino and then put the Arduino output straight in to an input on the breakout board?

The Arduino help on this site mentions a 470 ohm or 1,000 ohm resistor should sometimes be used when outputting? However, I have bought an 8 relay board that is designed for use with Arduino/Raspberry PI etc and that works fine with the Arduino output connected directly to the input?

Can anyone shed any light on the best way to do this?

Thanks :slight_smile:

Normally, connecting on Arduino to a computer does not pose any problems. The power supply that you normally use for the Arduino is a floating ground. The computers common terminal is connected to earth ground. If you have any doubts, use a voltmeter across the two grounds before you connect them together. The voltage potential should be zero.

If you need isolation, use optical couplers to isolate the two power supplies. Then you do not have to worry about grounds, they don't need to be connected.