My issue is fairly simple to describe but I have no idea what the problem could be. So I got my FONA 3G and immediately after taking it out of the box, I connected the battery and I wired up my FTDI board (aka USB to serial converter), and then I plugged it into my USB port to try and establish communication. I just tried the most basic at command AT(using PuTTy). You're supposed to get an OK in response but the FONA doesn't appear to even notice that I'm trying to talk to it. I type AT and press enter and nothing happens at all.

The issue is most certainly not my FTDI board, I'm very experienced communicating with wifi modules and other GSM modules using PuTTy. So please don't be concerned with the setup. That's 100 percent definitely not the problem.

I was able to send AT commands after plugging the module into my laptop directly using the module's USB input, but there is still some issue with its UART. I haven't been able to send or receive any communications directly from RX and TX. It wont respond to any programs I load up onto my arduino. Its like the UART is asleep.

If you have experience with FONA 3G, please speak up and tell me what steps you took to get the UART to respond. What should the status indicator look like before its ready to receive commands? Any knowledge you have about the FONA3G module would be helpful.

As a side note, the FONA3G has a chip number. It is SIM5320a. I don't know if that helps. Most people know it as FONA 3G.

  • While you say your FTDI setup is fine, are you 100% sure you haven't crossed the RX/TX lines?
    – hardillb
    Apr 30, 2020 at 11:13
  • Also are the levels (e.g. 3.3V/5V...) compatible? And of course the usual speed/bits/parity...
    – jcaron
    Apr 30, 2020 at 13:42
  • Of course, we'll suppose you have a battery with a compatible polarity. There are LiPo batteries wit the same connector but opposite polarities. In particular, most batteries for RC devices (drones etc.) have the opposite polarity to that used by Adafruit, Pycom, etc.
    – jcaron
    Apr 30, 2020 at 13:47
  • Do you have any LEDs lighting up? If I follow Adafruit's description, you should at least have a power LED on?
    – jcaron
    Apr 30, 2020 at 13:50
  • I said 100 percent certain the setup is fine. Not 99 percent. Of course I didn't swap the Rx and Tx. Rx goes to Tx and Tx goes to Rx. May 1, 2020 at 4:21

2 Answers 2


All right. Thanks to those of you who posted comments. It turned out to be an issue with the baud rate! Its always the simple stuff. Adafruit said this thing has auto baud meaning you can use any baud rate but they are wrong. It requires 115200 to work properly. Also I'd like to point out that there was nothing wrong with my setup. Sometimes you should trust the person when they say their setup is 100 percent fine.


Auto baud rate is only for the direct USB connection. The default baud rate of the TX/RX pair is 115200 baud. This is the baud rate set after a factory reset (AT&F1). Baud rate can be changed permanently with AT+IPREX= or temporarily (until next power up/reset) by AT+IPR=. Where is the actual baud rate i.e. 4800.

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