If you use sound card, a cable like this might be helpful (or not). I got a similar cable from work when they were throwing random stuff away. That is the only reason I learned of its existence. I would have never though of combining 3.5mm audio jack with DB9.

I think this will be better

 

Ok, thank you again for your replies

I don't have RS232 port on my computer, also I more prefer USB.

my signals have sampling frequency about 20 kHz and their length don't exceed 10 second

So, if I want to use USB what I hardware part I need and what software I need and what Ian field say [but beware - "thar be dragons"].

One of my recent motherboards had no RS232 on the back edge, but there was an easily missed header in the middle of the board.

FTDI (and others) do various TTL/RS232 & USB/RS232 converters - but compatibility issues aren't rare.

 

I think this will be better

Keep in mind:

1. The DB9 has 9 pins. 3.5mm audio has 3 pins. The DB9 on the cable has 3 pins out of 9 connected to 3 pins of the 3.5mm audio. The other 6 pins of DB9 are useless because they are not connected to anything.

2. The 3 pins of the 3.5mm audio are Right, Left, Ground (0 volts). Therefore the 3 pins of the DB9 will also be Right, Left, Ground (0 volts). So. Of the three pins, only two pins actually have the information signals.