Connect the serial module to your laptop and let's find out what name the OS assigned to it.

$ dmesg | grep -i tty
(..)
[  +0.000155] usb 3-2: FTDI USB Serial Device converter now attached to ttyUSB0

NOTE On macs, the USB device will named like this: cu.usbserial-*. Adjust the following commands accordingly!

But what's this ttyUSB0 thing? It's a file of course! Everything is a file in *nix:

$ ls -l /dev/ttyUSB0
crw-rw---- 1 root uucp 188, 0 Oct 27 00:00 /dev/ttyUSB0

You can send out data by simply writing to this file:

$ echo 'Hello, world!' > /dev/ttyUSB0

You should see the TX (red) LED on the serial module blink, just once and very fast!

Dealing with serial devices using echo is far from ergonomic. So, we'll use the program minicom to interact with the serial device using the keyboard.

We must configure minicom before we use it. There are quite a few ways to do that but we'll use a .minirc.dfl file in the home directory. Create a file in ~/.minirc.dfl with the following contents:

$ cat ~/.minirc.dfl
pu baudrate 115200
pu bits 8
pu parity N
pu stopbits 1
pu rtscts No
pu xonxoff No

NOTE Make sure this file ends in a newline! Otherwise, minicom will fail to read it.

That file should be straightforward to read (except for the last two lines), but nonetheless let's go over it line by line:

• pu baudrate 115200. Sets baud rate to 115200 bps.
• pu bits 8. 8 bits per frame.
• pu parity N. No parity check.
• pu stopbits 1. 1 stop bit.
• pu rtscts No. No hardware control flow.
• pu xonxoff No. No software control flow.

Once that's in place. We can launch minicom

$ minicom -D /dev/ttyUSB0 -b 115200

This tells minicom to open the serial device at /dev/ttyUSB0 and set its baud rate to 115200. A text-based user interface (TUI) will pop out.

Welcome to minicom 2.7.1

OPTIONS: I18n 
Compiled on Jun  5 2018, 10:54:41.
Port /dev/ttyACM0, 19:50:57

Press CTRL-A Z for help on special keys

You can now send data using the keyboard! Go ahead and type something. Note that the TUI won't echo back what you type (nothing will happen when you type) but you'll see TX (red) LED on the serial module blink with each keystroke.

minicom exposes commands via keyboard shortcuts. On Linux, the shortcuts start with Ctrl+A. On mac, the shortcuts start with the Meta key. Some useful commands below:

• Ctrl+A + Z. Minicom Command Summary
• Ctrl+A + C. Clear the screen
• Ctrl+A + X. Exit and reset
• Ctrl+A + Q. Quit with no reset

NOTE mac users: In the above commands, replace Ctrl+A with Meta.