I have a SixFab 3G/4G Raspberry pi hat and an EC25A modem. I have tried every way possible to change the APN stored in the modem. Of course, to do that, I need to send commands to that modem.
It should be noted that the SixFab hat / EC25 DOES work when I use a particular carrier (which does not require an APN).
I have tried the following:
#1. Removing the hat from the Raspberry and connecting a USB <-> Serial device to the TxD and RxD pins on the hat (6, 8 10). 115Kbaud, N,8,1, no handshaking, and powering the hat through the USB port. RESULT: No response when I type "ATZ .
#2. Putting the hat back on the Raspberry pi and loading Minicom, then setting Minicom to 115K N,8,1 no handshaking. I then connected my USB <-> Serial device RxD pin to first pin 8, then pin 10. to monitor the data flow. RESULT: The port displays typed chars when connected to pin 8, but nothing when connected pin 10.
#3. Loaded SER2NET so that chars sent over the net appear on the Pi’s serial port. I sent chars to the PI’s serial port and watched for response. I also monitored data on pin 8 using the USB <-> Serial converter. RESULT: Chars fed over the net appear on pin 8 of the Raspberry, but the EC25 does not respond.
What could I be doing wrong?