Using the curses library to view IoT data

Curses Windows

The examples so far have been based on a main screen object, but the curses library also supports windows. Windows are useful because they support border outlines, and text can be cleared from and written to windows without affecting the main screen object. The syntax to create a curses window object is:

mynewwindow = curses.newwin(  height, width, begin_y, begin_x)

The code for Figure 3,

# define a win1 window object
win1 = curses.newwin(9, 44, 6, 4)
# write text inside the window object
win1.addstr(8,0, "Sensor 1: Temperature Reading", curses.A_BOLD)
value1 = pyfiglet.figlet_format(  "23 C", font = "doom") win1.addstr(0,0,value1,curses.color_pair(2) )
Figure 3: Large text in two curses windows.

produces two curses windows. The major difference in the code is that information within a window is addressed by the window object instead of the background screen object.

Dynamic Bars

Simple progress or indicator bars can be created by a curses window with a border (Listing 4). The bar itself is generated by writing a space character with inverse video (Figure 4).

Listing 4

bar.py

01 import curses
02
03 bar = ' '   # with reverse video a space will show up
04 value1 = 10  # in real life this needs to be scaled
05
06 stdscr = curses.initscr()
07 curses.curs_set(0) # don't show the cursor
08
09 stdscr.addstr(1,3, "Python Curses Bar")
10 stdscr.refresh()
11 # Define windows
12 win1 = curses.newwin(3, 32, 3, 2)
13 win1.border(0)  # add a border
14 # a horizontal bar 10 characters wide
15 win1.addstr(1, 1, bar * value1,curses.A_REVERSE )
16 win1.refresh()
17
18 # Wait for a key press then exit
19 stdscr.getch()
20 curses.endwin() # restore the terminal to original settings
Figure 4: A simple curses bar.

After I had the basic curses bar working, I was able to use what I learned in the earlier examples to create Raspberry Pi interfaces that included color and large text (Figure 5).

Figure 5: Raspberry Pi sensor data presented as bars.

Summary

If you are looking for a quick and easy way to present data, without the bother of a GUI, curses is a great solution. Curses is supported in a variety of programming languages. I focused my curses work here on C and Python, but I've also had good success in Lua.

I only had one presentation issue and that was with line drawing characters like borders when I used Putty (a Windows-based SSH program). To fix this issue, I changed the Putty Window | Translation setting to use the VSCII character set; then, everything looked good.

The Author

You can investigate more neat projects by Pete Metcalfe and his daughters at https://funprojects.blog.

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