Thanks Robert, this is really helpful.
Now that I look at the LabX1 schematic, I'm thinking I don't even have to make this little circuit which I could whip up quickly. I should be able to grab the two signals (Tx and Rx) right off the LabX1 board, at least where the LabX1 is close to my project.

Another question: Is there a USB version for this? The LabX1 has serial input and your schematic shows a DB9 which I assume is serial interface as well. Pretty well none of my new computers have serial or parallel connections anymore, in fact I had to buy a serial PCI card for my computer just to run the debugger.