PC/CP320 Physical Computing

Raspberry Pi Python GPIO and Serial Console Introduction

Objectives

1. To introduce Python programming on the Raspberry Pi
2. To become familiar with Raspberry Pi GPIO pins and BOARD and BCM numbering schemes
3. To learn nano editor commands
4. To introduce using the serial console on the Raspberry Pi

Preparation

Equipment

• Raspberry Pi
• TTL-serial to USB adapter
• digital multimeter (DMM)
• LED and 1k resistor. (Depending on brightness, you may need a smaller resistor.)
• breadboard

Procedure

The Rapsberry Pi GPIO pins can easily be damaged with improper handling. For this lab, you will start by only connecting a digital meter to a GPIO pin.

1. Testing the Serial adapter driver installation

   Connect the TTL-serial cable via the USB cable to the computer,
   Open the Device Manager and check to see what COM port the adapter appeared on.
   
   
2. Open putty, and set it for serial on the COM port just noted and set the baud rate to 115200.
   
   
   
3. Any time you connect anything to the GPIO pins, make sure you know the correct orientation!!!
   
   Connect the TTL-serial cable to the Raspberry Pi as follows:
   
   • Don't connect the red wire.
   • Connect the black wire to GROUND.
   • Connect the white wire to TxD. Use a white wire for the connection!
   • Connect the green wire to RxD. Use a green wire for the connection!
   
   
4. Plug in the Pi, and you should see the boot process in the serial console and get a login prompt as expected.
   
   Show this to the lab instructor.
   
   
5. Here are some common commands for linux. Note that the cursor up and down keys take you through a history of previously used commands.

   Common linux commands
   Command	Description	Example
   ls	list files in directory	ls *.py
   cp	copy a file	cp test.py newtest.py
   mv	move (or rename) a file	mv oldtest.py newtest.py
   sudo	execute program as superuser	sudo python3 test.py
   mount	mount external (flash) drive	mount /mnt/usb
   umount	unmount external (flash) drive	umount /mnt/usb
   shutdown	shutdown computer properly	sudo shutdown -h now

   
   
   Here are some common commands for nano.

   Common nano commands
   Command	Description
   CTRL-K	cut line(s)
   CTRL-U	uncut line(s) (i.e. paste)
   CTRL-X	save and quit
   CTRL-O	save without quitting

6. Running the first python test program

   
   
   • Download gpio_test_basic.py according to the serial console wifi instructions.
     Note: An alternative way to copy a program is to
     1. Open the file on the PC
     2. Start the nano editor on the Raspberry Pi
     3. Copy the program from the window on the PC and paste it into the terminal window. (On the PC, copy with CTRL-C and paste in the terminal window by clicking the right mouse button.)
     4. Exit nano giving the file whatever name you want. (A good choice would be gpio_test_basic.py. )
     
     
   • Connect the meter to the GPIO pin to observe the output.
     Don't forget to connect the ground lead to one of the GPIO ground pins as well.
     
     
   • To run a program, type
     python3 gpio_test_basic.py
     
     (Note: typing "python" instead of "python3" will use python 2 instead.)
     
     Note: In some versions of Raspbian, you may need sudo to run programs which access GPIO pins.
     
     What is the voltage on the GPIO pin when it is HIGH?
     What is the voltage on the GPIO pin when it is LOW?
   • To exit a program type CTRL-C.
   • Now try to re-run the program. What happens?
     GPIO pins are not automatically released when a program stops. In order for this to happen you must release them before the program exits.
     
     
   • Download gpio_test_2.py
   • Run the program, as before, and then exit out. Rerun it and see what happens.
     This program makes sure that GPIO pins are released at the end. This is a template you should always follow.
     
     
   • Now connect the LED and resistor on a breadboard, and use the circuit in place of the meter to observe the program output.
     
     
7. Make a copy of the program so that you can edit the copy.
   To do this, type
   cp gpio_test_2.py test.py
   Now you can edit test.py using nano.
   To cut a line in nano, type CTRL-K.
   To uncut (i.e. paste) a line in nano, type CTRL-U.
   (Save and exit nano with CTRL-X.)
   (To save without exiting type CTRL-O.)
   
   
8. Modify the program to use the same pin GPIO18 but using the Broadcom numbering scheme. Show the modified working program to the lab instructor.
   
   

9. Backing up test programs to flash drive

   If you have a flash drive, in sert in into one of the USB ports and type
   mount /mnt/usb
   You should be able to use the cp command to copy files to the flash drive.
   You should be able to use the ls command to see that the files were copied to the flash drive.
   Before you remove the drive, be sure to unmount it using umount /mnt/usb
   Show this to the lab instructor.
   
   

10. Proper shutdown

    Shut down the pi using
    sudo shutdown -h now
    When shutdown is complete, all of the onboard LEDS will stop flashing, so you can turn off and disconnect power and put everything away.