Help - NTX2B and Adafruit GPS integration

[Alex Griffiths]

Hi all,

I am new to UKHAS so I hope this is the correct place to post this.

I am currently developing a long distance radio link for a HAB and have successfully managed to get the NTX2B transmitter working with my Arduino, altimeter and SDR dongle.

The issue I am currently facing is integrating the Adafruit GPS. The minute the GPS is switched on, even if I don't read the message, it corrupts the RTTY decoded message in fldigi. Initially i thought it was interference and tried physical shielding between them with tin foil (and moved them away from each other). I have also tried switching the enable off while transmitting but this effectively restarts the GPS and it has to find a fix again which can take minutes.

I think it is a timing issue or something to do with the software serial. Simply having the GPS.begin(9600) in void setup causes the message to be corrupted.

I can print the lat long values and if I Serial.print the datastring message it is fine, its just in fldigi where the message is corrupted. I'm not sure if I need some kind of interrupt to transmit or if there is a command that can stop the GPS sending serial data during transmission.

I have seen almost identical issues elsewhere on Arduino forums but the threads lead to dead ends.

If anyone can help or can point me in the right direction I would be very grateful.

Thanks

Alex

(photos and code attached)

[Sasha Tim]

Hi Alex!

Everything looks great! This is a very strange issue. 

I would say to try removing the power from the GPS or to remove the data wires and see whether it's a power issue (unlikely) or a data interference issue (also unlikely, but more likely than the other). 

Also - the NTX2 is now obsolete. What are you planning to do in the long run?

Best of luck!

73

VE3SVF

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/ukhas/e9bd2f8e-9e44-47b9-9207-7ea6c7019897n%40googlegroups.com.

[Alex Griffiths]

Hi Sasha/Ross,

Thank you both for your replies,

Ross:

I regards to the wiring diagram that's a mistake on my part so apologies for that,  the NTX2B radio pin is connected to pin 13 like in the software so I will change the diagram. Hopefully this is enough distance?

Sasha:

If I remove the GPS data wires then the message comes through fine, whether this is still  a software issue is still unknown.

I ordered a couple of NTX2B transmitters at the start of the project. I thought the NTX2B was the successor to the NTX2? When I called Radiometrix there was no mention of it going obsolete.

Thanks

Alex

[Alex Griffiths]

To close out:

I have managed to fix the problem (although in a slightly crude way). I had a dive into the software serial library:

Since turning the GPS off was not an option, nor was the ability to turn the GPS serial communication off without loosing a fix I took advantage of the Serial.listen() function.

Effectively I created a second serial channel on pins 8 and 9 (empty pins) and made the program listen to these empty pins while transmitting before switching back and listening to the GPS pins. This allows the GPS serial to be kept on but not interfere with the transmission.

I know going forward this isn't ideal as I may want to add additional modules that may need those pins but will at least allow me to do some testing.