BYO cable
I am too cheap to buy a cable to connect my PSR-310 to my computer. How would I go about building one? Both USB and Serial are okay for me.
If you want to do this as a fun activitiy, great. If you are doing it to save money, even if you value your time at zero, it is unlikely.
I have built a couple of different version cables. My goals were a lot higher because I wanted the USB aspect and I wanted the cable to work with any GRE made scanner I own. If you are only concerned with the newer models such as the '310, it makes it "simpler".
Here is a thread on the topic from not too long ago. The basic facts are: the '310 is a 3.3v design, but you should consider driving the signals to the scanner's PC/IF with open-collector. If you're just using a COM port (or COM side of a USB to COM adapter) signals can be from +/- 5v to +/- 15v, so level translation is needed. If you do incorporate your own USB to COM converter, your USB driver simply needs to present the cable as a COM port.