The error that I’m getting is when everything is connected with the below workflow, I only get the msg “$GPTXT,01,01,02,u-blox ag - www.u-blox.com*50”.
Workflow:
GP-635T GPS TX → RX Xbee Pro S3B → Xbee Pro S3B TX → Explorer USB (with RSSI cut mod) → Serial Console Putty
Xbee Pro S3B Set to 19200, port is 9600
GP-635T output is 9600
Troubleshooting:
I have verified that the GPS module is working fine by sending the GP-635T TX output to a standard FTDI cable and output is seen in the correct GPS format.
I have swapped the Xbee Pro S3B (900) with Xbee Pro S2B (2.4) and the GPS sentences are correct.
I have attached the Xbee Pro S3B output directly to another serial port and Tx/Rx transmission is correct.
The issue only occurs when I connect the GPS output to the Xbee Pro S3B input, is where I see the issue.
It does appear someone on the Xbee Pro S3B is loading down the GPS module?
What’s the problem? That is a valid message according to the data sheet. Do you give it enough time and free sky to detect the satelites? Or what did you expect to receive?
Xbee Pro S3B Set to 19200, port is 9600
GP-635T output is 9600
Doesn’t the GPS module talk in 9600 baud by default? Or 38400, as the datasheet seems to contradict itself. And what does “port is 9600” mean? Not that it matters, as you seem to get a good serial datastream.
Xbee Pro S3B Firmware set to communicate at 19200 between radios. UART is set to 9600. The GPS module outputs at 9600, not what it says in the datasheets.
GPS has perfect signal and works good going through a serial port directly connected to PC. I get all the sentences. It’s only when I connect the GPS output to the Xbee, is where all GPS sentences disappear with only outputting “$GPTXT,01,01,02,u-blox ag - www.u-blox.com*50”.
I have a few test rigs I setup to see where the issue is.
GPS output to serial port PC - output good, no issues
Xbee to Xbee - bidirectional communication is good with no issue
GPS output connected to Xbee - GPS starts to output only “$GPTXT,01,01,02,u-blox ag - www.u-blox.com*50”.
Probing between GPS and Xbee show the same exact string “$GPTXT,01,01,02,u-blox ag - www.u-blox.com*50”.
Disconnect Xbee and the full NEMA string appears
Reconnect GPS Tx to Xbee Rx, GPS output turns into only “$GPTXT,01,01,02,u-blox ag - www.u-blox.com50". Xbee is only transmitting "$GPTXT,01,01,02,u-blox ag - www.u-blox.com50”.
What I can gather is when I connect the GPS Tx to Xbee Rx, it causes the GPS module to go into a undocumented state. It appears the Xbee module is pulling down the line, causing the GPS module to go into a reset state.
Issue is solved. Found that the GPS is very sensitive to voltage changes. Range is 3.3 to 5.5 VDC. The Xbee Pro S3B voltage range is 2.4 to 3.6VDC. My power supply was set to 3.3v. Everytime there is a transmit from the Xbee Pro, the voltage would drop 0.3v. That would cause the GPS module to reset and go into a brownout state.
Bumped up the power supply to 3.6v eliminated the issue. Will need to put in a few voltage regulators in to isolate the power bus.
Don’t forget levelshifting of the TX and RX line, between the GPS and Xbee. Xbee’s can’t handle more than 3.3v Though you might still stay within the margins with 3.6, but it is borderline.
Maybe adding some buffering capacitors to the GPS voltage input might help too during the large current draw spikes of the Xbee.
leotech:
Issue is solved. Found that the GPS is very sensitive to voltage changes. Range is 3.3 to 5.5 VDC. The Xbee Pro S3B voltage range is 2.4 to 3.6VDC. My power supply was set to 3.3v. Everytime there is a transmit from the Xbee Pro, the voltage would drop 0.3v. That would cause the GPS module to reset and go into a brownout state.
Bumped up the power supply to 3.6v eliminated the issue. Will need to put in a few voltage regulators in to isolate the power bus.
XBee Pro S3B is a 900/868MHz radio, with relatively high (optionally chosen) transmitter power. Consumes lots of power while transmitting.