** UPDATE Windows 10 **
We have amassed quite a collection of USB to RS232 adaptors
and boxes over the years and we have been less than impressed
with many. However, Windows 10 seems to be a big leap forward,
as many of the devices that refused to work in previous Windows
versions are now fully operational and reliable in Windows
10! It would seem that many manufacturers have bit the bullet
and written proper device drivers for their adaptors at last.
We will of course monitor the situation as time progresses.
Since the release of Windows XP many laptop manufacturers
no longer have a "proper" serial port at the back.
Notable exceptions are quite recent IBM Thinkpads and some
Dells with the docking station. Instead there are only USB
ports. As a result users are finding that a USB to serial
adapter is the only way they have to communicate with their
Unfortunately all USB convertors are not created equal, especially
if they contain the "prolific" of "fdti"
chipset (But see Windows 10 update above). Devices intended
for use at home are now expected to work in the harsh industrial
environment, and unfortunately many are not up to the job.
Many manufacturers of USB to serial adapters are not 100%
compatible and communication to with CNC machines is either
unreliable, very slow, or limited to one way transfer.
For a great technical explanation of the differences between
"proper" serial ports and a USB convertors, click
For laptops we recommend you use a PCMCIA/Express to serial
card if you have an available slot (newer laptops don't do
them anymore). They are far superior and often not much more
expensive, preferably with some form of isolation. We have
several Quatech and Brainbox cards and found them to be very
reliable, in addition they have all the required drivers for
almost all versions of Windows. These devices are much less
common today and you will struggle to buy quality new ones,
but they are often available at bargain prices on ebay.
If you want a reliable USB device, then we have used Keyspan
USB to RS232 adaptor cables - they work great when others
just don't >> Click
Here or Here
and are reasonably priced. We have reports from several users
are also reliable.
Please take time to watch this video for additional information
and resources about USB devices from BB-Electronics. This
company sells more robust rugged USB devices (albeit more
expensive) much more suited to industrial applications www.bb-elect.com.
Often it is worth spending more money initially, than wasting
time when you cannot get the USB to work.
Unfortunately it's not as simple as listing USB to RS232 devices
that work for one user, because sometimes the same one will
not work for another. So whilst we list several options above,
there is just no 100% guarantee that any will work with your
Quite often we think that it is well worth the while to buy
a secondhand laptop off ebay with a proper serial port. In
many cases this would work out cheaper and far more reliable
than having to buy things such as USBs or Express cards.