Setting Up the Display

The sample program Display.py shown in Listing 4 is designed to display the text passed in as a parameter on the display. The system controls the screen with the help of the ST7735 library [5], which was specially developed to transfer image data to the display.

01 from PIL import Image
02 from PIL import ImageDraw
03 from PIL import ImageFont
04 import ST7735
05 import sys
06
07 display = ST7735.ST7735(port=1, cs=0, dc=23, backlight=None, rst=16, width=128, height=160, rotation=0, invert=False, offset_left=0, offset_top=0 )
08 image = Image.new('RGB', (display.width, display.height))
09 draw = ImageDraw.Draw(image)
10 print (len(sys.argv))
11 if len(sys.argv) < 2:
12     print ("Usage: Display.py <TEXT>")
13     sys.exit()
14 draw.text((0, 70), sys.argv[1],  font=ImageFont.truetype("UbuntuMono-RI",10), fill=(255, 255, 255))
15 display.display(image)

To generate the appropriate image data, access the Pillow [6] image processing library. Pillow (also known as PIL) is a very powerful library with a large number of functions, of which I will only be using a few. The documentation [7] will give you a rough idea of what you can do with Pillow.

When launched, the Display.py script first imports (lines 1 through 5) the ST7735 library, the required parts of Pillow, and the sys library, which lets you read the arguments from the command line. After that, the code creates a display object with parameters suitable for the hardware you are using (line 7).

Line 8 generates an image of a size suitable for the display and stores it in the image object. The commands that follow generate text from the parameter passed in at the command line and insert the text into the image (line 14). The last command then transfers the image to the display.

If you run the program with the

python3 Display.py "Hello world!"

command, the Hello world! output immediately pops up on the screen.

Configuring the RFID Reader

The program in Listing 5 reads the individual UIDs from the RFID chips (line 10) and displays them on the screen (line 13). The display is addressed by an external call to avoid the libraries for the display and the reader getting in each other's way. After outputting the UID, the program reads the first four data blocks from the RFID chip in a loop (starting in line 14) and displays them, too.

01 import os
02 from pirc522 import RFID
03 rdr = RFID()
04
05 while True:
06   rdr.wait_for_tag()
07   (error, tag_type) = rdr.request()
08   if not error:
09     print("Tag detected")
10     (error, uid) = rdr.anticoll()
11     if not error:
12       print("UID: " + str(uid))
13       os.system('python Display.py "'+str(uid)+' "')
14       for block in [0,4,8,12]:
15         (error,data)=rdr.read(block)
16         print("[ %02d]:"%(block),end="")
17         for c in data:
18           if c<=15:
19             print ("0%x "%(c),end="")
20           else:
21             print ("%x "%(c),end="")
22         print("|",end="")
23         for c in data:
24           if c>65 and c<123:
25             print (chr(c),end="")
26           else:
27             print(" ",end="")
28         print("|")
29 # Calls GPIO cleanup
30 rdr.cleanup()

Note that the reader does not authenticate against the chip, which means that the sample program can only read unprotected chips. If you want to delve a little deeper into the topic of RFID authentication, you can refer to the RC522 library documentation [8].

I used several smartphone apps to program the chips. NFC Tag Reader [9] is great for getting started and offers numerous functions, although it does have a lot of annoying advertising.

The ad-free team of NFC TagInfo [10] and NFC TagWriter [11] delivers a plethora of information that can be a bit confusing for newcomers; however, breaking the functions down into two apps makes the tools easier to use.

The MIFARE Classic Tool [12] is optimized for working with RFID chips from Mifare and supports authentication. The S50 card included with the reader kit I used in the test, and the RFID tag also included, both support this method.

Conclusions

This article can provide a basis for your own experiments with RFID chips. For many applications, simply reading the tags is enough to get a result. The Pillow library, which I used for the screen output, is also well worth a closer look. Its capabilities go far beyond simply popping up text on a display.