AK-USB-RS485-HD Line Driver

User manual for the Artekit AK-USB-RS485-HD, USB to RS485/422 bridge.


Introduction

The RS485, also known as TIA-485(-A), EIA-485, supports serial communications using balanced mode (differential pair) and supports also multipoint systems. Can be used over long distances in electrically noisy environments.

The AK-USB-RS485-HD board is an USB-to-RS485/422 bridge that converts USB into RS485/422 signals, and can be used to connect your PC/MAC/Raspberry Pi to a network of RS485/422 devices.

The USB bridge is achieved by the well known and widely used FTDI FT232RL chip and the board is powered directly through USB cable.

Hardware

You can connect the board to your host device using a standard mini USB cable. The board is powered using the 5V from the USB cable, so no external power supply is required.

Screw terminals

The AK-USB-RS485-FD board comes with or without soldered screw terminals that allows you to easily attach the wires to the board. You can choose to include the soldered screw terminals at the moment of purchase.

Indication LEDs

The board has two LEDs to indicate TX and RX activity. The yellow LED indicates RX (incoming data) activity, and the green LED indicates TX (outgoing data) activity.

The AK-USB-RS485-HD data flow is automatically controlled through 2 control pins, TXE (Transmit enable) and RXE (Reception enable) provided by the FT232RL device. A solder option pad allow the echo cancellation. The device is powered directly trough USB cable.

Solder jumpers

At the back of the AK-USB-RS485-HD board you can find two solder jumpers. One is used to enable the on-board 120 Ohm load resistor in parallel with the network cables. To enable the resistor, drop some solder to create a short circuit between the LOAD pads. This option must be applied only on the first and the last boards in the network.

The other solder jumpers is to enable/disable the character local echo. Create a short circuit with solder accordingly to the following picture. Do not use both echo options at the same time.

The character echo is disabled by default.

Connecting the network

The next picture shows how to connect the AK-UAB-RS485-HD board to a RS485/422 network.

Connecting the board to the host

The AK-USB-RS485-HD board is seen by the host as an USB-to-Serial converter, and is accessed through a virtual serial port.

In order to use the board as a virtual serial port you need to install some drivers. On modern operating systems (Linux, Windows 7 and up, OSX) the drivers should be already installed, or will be downloaded automatically when you plug the board in for the first time.

In the case you still need to manually install the drivers, you can find them in the FTDIchip website: https://www.ftdichip.com/FTDrivers.htm

There are two kind of drivers: VCP drivers for Virtual COM Port emulation (this is the most commonly used and the one that is automatically installed) and D2XX that allows you to access the USB-to-Serial converter through a special library for advanced usage.

We recommend the VCP drivers that will quickly allow you to use the board with programs like TeraTerm or PuTTY.

When the drivers are correctly installed, the host “sees” the board as a new COM port on Windows or ttyUSB on Linux.

Testing your setup

After you have installed the drivers you want to make sure that everything is working as it should with this simple local-echo test:

  1. Disconnect the board from the RS485/422 network.
  2. Enable the character echo with the solder jumper.
  3. Connect the board to a USB host using a mini USB cable. A virtual serial port should be generated.
  4. Launch you preferred terminal program.
  5. Select the virtual serial port for the board.
  6. Disable the Local Echo in the terminal program.
  7. Press any character key.
  8. Check if the transmitted character is read back in the terminal program.

If the transmitted character is read back, the setup is OK. If the Local Echo option is not disabled in the terminal program, you will see two characters returned, one from the board and another from the local echo.

Additional resources