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New FONA 3G Serial Communication Not Working
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New FONA 3G Serial Communication Not Working

by rmlait on Mon Feb 22, 2021 12:57 am

Hi,

FONA 3G Module - Serial Communications port not working out of the bag.

I purchased a FONA 3G module (Order 2474341-6430390657), but out of the bag, the serial communication port is not working. I can see data from my controller being sent to the module, but the module does not respond. The module does seem to be partially working in that I can see from the flashing LEDs that it does connect to the cellular network.

My bench test for the module consists of connecting the module to a Feather M0 and running code from my working FONA 3G projects as well as using the Adafruit FONA Test sketch.

To further troubleshoot I swapped the new FONA 3G module with a FONA 3G module from one of my completed projects. The FONA 3G module from the working project works as expected in the same bench test as the new defective module.

I would like to get an RMA going so that I can get a working module.

Please advise.

Thanks,
Russell



This is the second FONA 3G modules that I have purchased.

rmlait
 
Posts: 5
Joined: Mon Feb 04, 2019 5:11 pm

Re: New FONA 3G Serial Communication Not Working

by rmlait on Thu Feb 25, 2021 12:53 pm

While waiting for a response I decided to reflow the solder on the 74VHCT125 buffer IC1 and that seems to have fixed the problem. I can now get the device to work as expected on my bench test, and it also works when I just connect it to a simple USB to serial.

While going through this exercise I also started looking at baud rates. Prior to deciding to reflow the solder on the serial buffer I was trying to see if changing the baud rate had any effect on the problem.

That said, the FONA-3G documentation indicates that the RX and TX lines will auto-baud, but that does not seem to be the case.

Looking at the value returned by AT+IPREX? both this module and the one I have deployed in a production project return no value. The SIM5320 manual says that if no value is set the device will default to 115200. Fair enough. The AT+IPR command temporarily will set the baud to a given value and after a reboot of the module the baud is supposed to go back to the default value which is 115200 or whatever value may have been set using the +IPREX command.

The only reference I see to autobauding in the SIM manual does not look like it relates to this serial port. E.G. AT+CBST Select bearer service type: AT+CBST lists autobaud being one of the options, that is carrier related and I did not think had any association with the RX and TX pins.

There is a good chance the problem is between the keyboard and chair, and if so please help me understand if and how the RX and TX pins are set to autobaud.

Thanks,
Russell

rmlait
 
Posts: 5
Joined: Mon Feb 04, 2019 5:11 pm

Please be positive and constructive with your questions and comments.