AT command gives no response

Question

I have a Raspberry Pi 3 running Raspian Lite

pi@raspberrypi:~ $ uname -a
Linux raspberrypi 4.14.79-v7+ #1159 SMP Sun Nov 4 17:50:20 GMT 2018 armv7l GNU/Linux

I am following this tutorial, setting up an Adafruit Fona 808 for GSM/GPS connections. I've installed screen and pppd as instructed.

pi@raspberrypi:~ $ sudo apt-get install screen ppp
Reading package lists... Done
Building dependency tree       
Reading state information... Done
ppp is already the newest version (2.4.7-1+4).
screen is already the newest version (4.5.0-6).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

The problem is that when I start screen and enter 'AT' I get no response.

I start the screen session like so:

pi@raspberrypi:~ $ sudo screen /dev/serial0 115200

I see a black screen with blinking cursor. I enter 'AT' on my keyboard but no characters appear on the screen. I press enter, still nothing appears.

I'm using screen version 4.05.00

pi@raspberrypi:~ $ screen --version
Screen version 4.05.00 (GNU) 10-Dec-16

I am not sure how to troubleshoot this issue.

Any suggestions?

Answer 1

Running the following:

pi@raspberrypi:~ $ sudo ls -l /dev/

I noticed that serial0 is pointed at ttyS0

lrwxrwxrwx 1 root root 5 Feb 3 23:49 serial0 -> ttyS0

So, running the following worked:

pi@raspberrypi:~ $ sudo screen /dev/ttyS0 115200

In screen:

AT
OK