RTK Express+ Data Port NMEA codes unintelligible.

[jpherron]

I have an RTK Express+ that I am trying to look at the NMEA output on the data port.

Measurement Rate: 10 Hz

Logging to SD card: Enabled

Serial Port Baud Rate: 460800

Data Port Mode: NMEA TX Out/Rx In

Message: Set to Surveying Defaults (5 messages)

Computer Terminal Settings

Bause Rate: 460800

Data: 8 bit

Parity: None

Stop Bit: 1 bit

Here are a couple of line of what the terminal output looks like.

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I’ve tried slower measurement rates. Turning the data port setting to a different mode and then back to nmea.

Is it possible that there is something wrong with the data selection device that is sending the NMEA codes to the data port? If I plug in the usb cable i get the nmea codes across the internal usb-to-serial chip just fine.

[sparky]

I’ve got an Express + humming away on my desk at 10Hz and 460800bps. Be sure the terminal program on your computer is set to 460800bps. Be sure the port on the Express Plus is set correctly as well. See images:

[sparky]

Is it possible that there is something wrong with the data selection device that is sending the NMEA codes to the data port?

Yes it’s possible but I’ve never seen it. It’s just an analog mux.

https://docs.sparkfun.com/SparkFun_RTK_ … onnection/

Be sure the green TX wire goes to the RX pin on your USB to serial board.

[jpherron]

I purchased two express+ units and I just tested the second with the same configuration, but using a different usb-to-serial adapter. I ended up with the same garbled result.

I thought maybe the usb-to-serial adapter didn’t support 3.3V I/0, but I looked up the FTDI 4232 chip it uses and it is 3.3 v compatible so that Idea wasn’t useful.

I would appreciate any advice.

I have included screenshots of the terminals for the serial ports.

[sparky]

You may want to open u-center and verify that UART1 port is set to the baud you expect.

Possibly try a different terminal program. Possibly swap TX/RX pins to make sure you haven’t got things backwards.

[jpherron]

I get the same output using both putty and tera term. I also tried two different computers.

I’ve attached the u-center info for uart1 from the config section of the messages.

[jpherron]

One additional thing that I noticed that is odd. If I have the ground (black) and TX (green) cable from the unit plugged into the serial port the power button works fine. If I have the RX cable (orange) plugged into the serial port as well I can turn the unit off, but I have to unplug the RX cable before the power button works to turn the unit on again.

[sparky]

I’ve attached a photo of my setup. Be sure you’re in the DATA port. Note that 3.3V from the USB to serial IC is not attached to the unit as this will back drive the voltage.

I’ve got both a very old unit and a very new unit and both behave identically and correctly output NMEA at 4Hz at 230400 and 10Hz at 460800.

[jpherron]

Here is my setup. You may notice that I used opposite colors on the tx and rx lines on the port, but the green tx is going to rx (pin 2) on the port.

[PaulZC]

That looks like a good old fashioned 9-Pin D RS232 port? It will be expecting higher voltages and the opposite polarity…

Best,

Paul

[jpherron]

Ran over the standard electric and picked up a usb to serial converter based on the FT232RL chip and the serial comms worked fine. For my application I need to connect to an old school serial to IP adapter to transmit the GPS locations of a vehicle on a computer in real time. Looks like a the RS232 shifter would do the trick.

[PaulZC]

One of these might come in handy:

https://www.sparkfun.com/products/449

Check that pins 2 and 3 match your port (it’s an old school DTE vs DCE TX/RX issue) but - if you unscrew the 4-40 inserts - it may be a perfect match for your ports.

I hope this helps,

Paul