I tried to hook up the data port today to an old style DB9 connector. I used the 4-pin JST cable supplied with the kit so assume the following:
Pin 1 = Red (3.3v)
Pin 2 = Cyan (TX) >> DB9 Pin 2 (RX)
Pin 3 = Orange (RX) >> DB9 Pin 3 (TX)
Pin 4 = Black (GND) >> DB9 Pin 5 (GND)
When connected up the RTK Express screen freezes, and I get garbage at the default baud rate of 460,800. I used the ESP32 port (using USB-C) and ensured only NMEA messages (x5) were selected, then went into the port options to check that NMEA in/out was selected and baud rate was correct. No changes I made delivered anything but garbage (even when configuring and bring baud rate down to 9600).
I even changed to a different USB to serial adapter (and a different workstation) and got the same result…
Any help would be great. Thanks in advance.
DB9 (and DB25) serial ports are usually +/- 12 volts and the serial is inverted from the 3.3 volt TTL level serial devices like the RTK express uses. You need a converter like a MAX232 to do the conversion for you.
Be aware, you might have damaged your device but give something like the item in the link below a try.
https://www.sparkfun.com/products/11189
I’m confused, you will have to entertain me. The hook up guide and schematic all show 3.3v:
https://cdn.sparkfun.com/assets/learn_t … ematic.pdf
I’ve not got pin 1 power connected anyway (only TX,RX & GND). The hook up guide implies its good to go and not needing another board to get serial comms?
Had a quick probe of both ports:
Radio:
Pin 1 = 3.8v
Pin 2 = 3.3v
Pin 3 = 3.3v
Data (configured as NMEA out/in):
Pin 1 = 3.3v
Pin 2 = 1.4v
Pin 3 = 2.9v
Is the device you’re connecting to RS232 or TTL serial? If it’s RS232, you need an adapter to correct voltage and data polarity.
RS232… Umm guess the penny has dropped and I look monumentally stupid now! Too many years of tinkering and this has never come up surprisingly. In my defense nowhere on the hook up guide does it imply that this port is TTL serial. That could be clarified, and now I get your original post about +/-12 volts. I will get an adapter as you suggested, but probably a cabled or dongled one so not exposed.
I re-read you post and you made it clear it was TTL serial, so apologies again!
Thanks for your help.
