I have a system that communicates between PIC32MX250F256D (USB module) and PC via USB (2 meters apart). And I need to increase the range of this communication to 100 meters. Due to typical 5m limit of USB, I am thinking of using 2 USB to RS485 PCBA from FTDI and connect their RS485 sides together to increase the cable length to 100 meters. In this way, one USB side will go to PIC32MX250F256D and the other to PC. The PIC circuit or code cannot be altered. Whatever I do can only be done after PIC. The communication is 2-way. Baudrate is 115200. The reason for not using USB hubs is to keep the cable system clean as this solution will be mass produced if it works. My question is to know if this would work and what problems do you guys see in this? Any recommendations are more than welcome.

  • \$\begingroup\$ I believe there are USB-optical cables that can go maybe that length? \$\endgroup\$
    – Joren Vaes
    May 10, 2020 at 9:38
  • 1
    \$\begingroup\$ the FTDI bridging solutions normally act as USB device and cannot be used as Host-Controller, which means your PIC32MX250F256D has to act as the host. Did you check if it is able to correctly address the FT? Tbh I doub that this is easy to achieve. \$\endgroup\$ May 10, 2020 at 9:50
  • \$\begingroup\$ @JorenVaes you are right but they are extremely expensive and not financially viable. I need a cheap solution \$\endgroup\$
    – Ahmed
    May 10, 2020 at 9:54
  • \$\begingroup\$ Cheap and high performance don't go together. \$\endgroup\$
    – MadHatter
    May 10, 2020 at 15:35
  • \$\begingroup\$ @ChristianB. my PIC is in USB Device mode. And it needs to be in this mode as it must be able to communicate with the PC. Looks like this won't work. I need another solution. :) \$\endgroup\$
    – Ahmed
    May 11, 2020 at 9:05

1 Answer 1


If you cannot alter the PIC code, how is it going to recognise the ftdi device and program it to 115200 bd? You need to search for "transparent usb over ethernet" or extender or similar. One such device found on amazon for about $60, consists of a usb->ethernet cable box, an ethernet cable (probably not compatible with real ethernet), and an ethernet->usb hub box, which needs its own power supply.

The host sees a usb hub in front of the PIC device, and the PIC sees a usb host as usual.


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