5 Steps for Choosing the Best USB to RS485 Converter

If you need to connect a serial RS485 device to your computer but your computers doesn't have a serial port, then the easiest and fastest way to do that is by using a USB to RS485 converter. Finding the best converter can however be a challenge since there are so many different models, types and manufacturers. These 5 steps will help you make the right decision.

1. Preferred processor chip: FTDI or Silabs (very reliable)
2. Preferred serial driver chip: ZyWyn, Maxim or NI (very reliable)
3. Minimum 5.0VDC output power at serial connector (ensures reliable data transmission)
4. Build-in electro-static protection for at least 600W (protects against static electricity)
5. LED lights for TX and RX activity (nice to have when troubleshooting)

U.S. Converters sells a line of USB to RS485 converters that offers all the above features. We recommend the converters shown below for all newer operating systems. Both converters has the same features and high quality only the physical appearance is different. Simply choose the model that is most suitable for your project:

1. Preferred processor chip: FTDI or Silabs.
   This is the most important step. The reason why we highly recommend a USB to RS485 converter with a processor chip from either FTDI or Silabs is because these are simply the best and most reliable. We have extensive experience with these and tests have shown us that these processor chips work with the majority of devices and equipment on the market. The drivers are very stable, easy to install and compatible with all versions of Windows 32/4-bit, Mac, Linux.


2. Preferred serial driver chip: ZyWyn, Maxim or NI.
   The serial driver chip is what is actually communicating and providing the power signals for your device connected to the USB to serial converter. We recommend a brand name driver chip from ZyWyn, Maxim or NI because these are very reliable and works well with the FTDI and Silabs processor chips.


3. At least 5VDC output power at serial connector.
   We recommend a USB to RS485 converter with at least 5VDC power output for the TX/RX signals. This will ensure a strong communication signal and that your device gets sufficient power. The output power is measured from signal ground to the Tx signal and the Rx signal.


4. Build-in static protection to at least 600W.
   Built-in static protection protects the USB to RS485 converter against high voltage spikes created either by static electricity or by surges in the supply voltage. This problem can exist both at the USB end and the serial RS485 end.


5. LED lights for TX and RX activity.
   Not required but very nice to have. Being able to actually see when data is transmitted through the converter is a big advantage when troubleshooting. This way its easier to find out where the problem lies; if its your computer, your device connected to the converter or the converter itself.

• Avoid converters with a low-cost processor chip such as Prolific. The drivers are poorly written, incompatible with newer operating systems and creates unreliable communication.
• Avoid converters with a low output power (less than 5VDC). Low output power makes the communication unreliable or even impossible.