The HobbyCNC boards are compatible with Arduino, Raspberry Pi and others. HobbyCNC boards accept standard “Step and Direction” TTL level signals via a 25Pin D male connector.
The 25 Pin D connector is a reliable, robust and low-cost connector that is well suited for applications such as this.  The pin-out is designed to be pin-for-pin compatible with a standard PC parallel port, however this does not prevent connecting the board to other systems.
The actual pin-outs of the connectors are provided on each product’s page (scroll to the bottom of the page!)
One way to access these pins is to use a 25 pin D, female, solder connector (Figure 1). You can add only the wires you need.
A steady hand is needed, but this is a good, reliable and inexpensive way to get to the connections.  A “hood” or “shell” is also strongly suggested to protect the wires from the strain of plugging/unplugging (Figure 2).
Figure 1 – 25 Pin D, Female connector, solder cup.
Figure 2 – hood parts (top), assembled (bottom)
Arduino name is a protected trademark of Arduino LLC.
Raspberry Pi is a trademark of the Raspberry Pi Foundation.