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Why isn't my USB to Serial adapter working?

** 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 CNC machines.

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 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 here.

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 either). 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 and are reasonably priced. We have reports from several users that MOXA 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 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 computer.

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.

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