In some versions of Windows, it will complain that the INF driver 
"doesn't contain digital signature information." This is because I didn't pay 
Microsoft thousands of dollars. 

The workaround for this, if it's needed, is to temporarily disable Signed Driver
Enforcement, which you can google for, or try these instructions:

Windows 10: 

Click the Start menu and select Settings.
Click Update and Security.
Click on Recovery.
Click Restart now under Advanced Startup. 
     (the computer will reboot into a startup menu)
Click Troubleshoot.
Click Advanced options.
Click Startup Settings.
     (the computer will reboot into another startup menu)
Click on Restart.
On the Startup Settings screen press 7 or F7 to disable driver signature enforcement.
     (the computer will reboot back into your normal desktop.)


Windows 8 (maybe?):

press Windows + I, which should bring up a Settings panel.
go to "Change PC settings"
click "General"
click "Advanced Startup"
click "Troubleshoot"
click "Advanced Options"
click "Startup Settings"

the computer will reboot into a windows config menu, 
from which you should select "Disable driver signature enforcement"
     (the computer will reboot back into your normal desktop.)


Once driver signing enforcement is disabled, you will be allowed to install
the INF file by clicking an "Are you sure?" dialog.   Note that it may still 
display the "does not contain digital signature information" error box, but
now it will have actually installed the INF file anyway. It's probably wise to
re-enable driver signing enforcement afterward. 

fetch the INF file from:
http://teletweety.com/usbtty_adapter.inf
and save it to your desktop, then right click and choose "install."


NOTE.
For what it's worth, you are not actually installing a driver (or any software)
here at all.  All versions of Windows already include the correct driver, and
the INF file is only needed to tell Windows to use it for this particular device, 
which it's never heard of.

If you find a better way of doing this, or work out how to do it 
on other versions of Windows, please let me know so I can update these
instructions. 

eric