There are many ways to talk to USB relay controllers, some manufacturers choose HID or Custom USB communications to gain a performance advantage.  HID USB protocols do not require a driver, they use a standard HID descriptor to communicate relay control data.  Most computers support HID protocols, so HID commands are relatively easy to handle, but the software can be a little complex, so an extensive library of samples should be provided for all HID based USB relay boards.

Other relay control manufacturers support custom USB descriptors, which require a driver for each platform.  These devices are more limited by platform unless the manufacturer has provided a USB driver for each platform.  This would be my least favorite type of USB device unless it were well supported with tons of samples.  Watch for OS upgrades, as these kinds of drivers may require updates.  Newer operating systems can easily render older drivers obsolete, leaving your hardware useless.

We use VCP drivers to communicate to our relay controllers.  VCP stands for Virtual COM Port.  Essentially, we use good old fashioned serial communications to communicate data to our USB relay controllers.  The advantages of this protocol are abundant:

  1. VCP Drivers are available for EVERY Computing Platform, including Windows, Linux, MacOS, even Android and other specialty platforms.

  2. Mechanical relays are slow to respond, with a typical reaction time of 5-10ms, so there is no speed advantage to using USB at high speeds (serial data can easily outrun the recommended switching speed of a relay)

  3. VCP communications is easy to work with EVERY programming language, all you need to do is make sure your language supports serial communications.  If you can send serial data, you can talk to a VCP controller.

  4. Serial communications is by far the oldest and most widely used computer to computer hardware communication platform in the world and despite it’s age, it is still widely used in the most modern of embedded systems.  While few motherboard manufacturers include a serial port, it’s still used extensively for embedded systems to talk to other embedded systems.

  5. A COM based platform ensures an upgrade path to other communication technologies.  Our VCP relay controllers can be easily converted to industrial wireless, ethernet, WiFi, bluetooth, RS-232, and even Cloud based relay control infrastructures because all of these technologies support COM communications.