DIY Kerlink Wirgrid debug probe

(repost of https://forum.loraserver.io/t/schematic-kerlink-wirgrid-debug-board/3837/2)

If you happen to mess up the network or firewall config on your Kerlink gateway, the only way to get back into it is using a Wirgrid Debug probe. These things are really expensive and/or difficult to get your hands on. Looking at the photos of this debug probe one will see that it uses an FTDI FT232BL. This is a USB to serial chip which is very often used in USB to Serial/UART modules. This confirms that there must be a serial interface on the Kerlink’s debug port. From experimentation I got a working terminal via the debug port using a Sparkfun FTDI basic breakout for 3.3V: https://www.sparkfun.com/products/9873

The pinouts of the debug header on the Kerlink itself I used are as follows:

# 1
2 #     O TEST
# 3
4 #
# 5
6 #
# 7
8 #
        O RESET
  1. Vcc?? - unsure about this
  2. Looks like Reset
  3. TX (connect to dongle RX) - reads as 3.3V on a multimeter, indicating 3.3V TTL logic - so use a 3.3V FTDI breakout.
  4. RX (connect to dongle TX)
  5. Looks like Boot
  6. Ground (connect to dongle ground)
  7. ??
  8. ??

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Do you remember if you needed to log in? Version 2.7 (August 2016) of “Installation and Maintenance Manual Long Range IoT Station (Lora Station)” says:

It is also possible to access to the debug interface by Ethernet connection by connecting directly to the POE injector or the Ethernet switch (depending on the installation topology).

That makes me wonder if connecting directly to the ethernet connector behaves differently than connecting through a network.

Indeed; some more details from that document:

The Wirgrid Debug Board is intended to be connected to the debug interface. It is mainly a simple UART to USB converter.

The main characteristics of the Wirgrid debug board are:

Characteristics Specification
UART Interface Micromatch 8 contacts connector
External power supply on pin 1
Up to 1Mb/s
USB2.0 interface USB 2.0 A type
USB Self Bus Powered at 5V
Full Speed (12Mb/s)
Operating temperature range 0°C to +60°C
Chipset FT232BL (FTDI)

debug probe