Raspberry pi II

See the first raspberry pi lesson for connecting to the raspberry pi with SSH.

Connecting Arduino to the Raspberry pi

  • We can make the connection with the comport object as we have done before on the desktop. It’s a good idea to upload your Arduino sketch on your desktop, and afterwards connect the Arduino to the Raspberry Pi.
  • Or you can use Pduino
    • Make sure that you have StandardFirmata uploaded to your Arduino, then connect it to one of the USB ports on the raspberry pi.
    • The arduino object in pure data runs on the raspberry pi as well.
    • You should be able to run all the things we have made during the course with pduino.

Running pd standalone

  1. I have prepared a simple pd example that can run standalone. Download the example by running
    “wget https://dl.dropboxusercontent.com/u/14056702/PID/potsynth.zip”
    in the terminal. (The wget-command downloads files from URL’s.)
  2. Expand the archive by running “unzip potsynth.zip“.
  3. You should now have a folder called potsynth in your home folder. Check by running “ls” (list files command).
  4. wget https://dl.dropboxusercontent.com/u/14056702/PID/pd%2Barduino.zip
  5. Run “pd-extended” on the raspberry pi and browse for potsynth/simplest.pd
  6. On the left side you can see what we need to start the DSP and connect to arduino.
  7. The right side contains all necessary elements for a simple synth that we control from analog input 0 on arduino.

Running programs on boot

  • We can add commands to a file with the name /etc/rc.local to run them immediately when the system has booted up. When the system boots, it will look in this file and run the commands that are present there.
  • Run “sudo nano /etc/rc.local” to open the file in a text editor.
  • Add this line:
    /usr/bin/pd-extended -nogui /home/pi/potsynth/simplest.pd &
    after the comment (lines starting with #) in the text file. This is the command that will run on boot. Explanation of the line:

    • We need the full paths for the commands and files (/usr/bin/pd-extended instead of pd-extended).
    • -nogui is an argument for puredata that tells it to run on the command line only.
    • The &-sign at the end of the line tells the command to run in the background.
  • Press ctrl+X to close the text editor and answer Y to save the file. If it asks for the filename, press enter.
  • Now, each time after you start up the raspberry pi (“sudo reboot“) your Raspberry pi, the code will run automatically, so you don’t need a keyboard or network connection for operation.

Shutdown button

  • As we were talking last time, it’s not a great idea to plug out the power of your raspberry pi without running the shutdown command.
  • Here is a python script that shuts down your raspberry pi if GPIO pin 7 is connected to ground.
  • You can download it on your raspberry pi by running:
    “wget https://dl.dropboxusercontent.com/u/14056702/PID/shutdown.py“
  • Add the python command to the /etc/rc.local file in the same way as we did with the pot-synth in last exercise. This is the line:
    /usr/bin/python /home/pi/shutdown.py &
  • Now you need to connect your shutdown button here:
    raspberrypi_shutdown
  • Again, you need to reboot (“sudo reboot“), for the changes to take effect.
  • Pressing this button after startup will now shutdown your raspberry pi in the proper way.

Notes:

Sudo command

  • The sudo command runs other commands with admin rights.
  • If you try to run something and it doesn’t work, especially if there is some error about permissions, running it with sudo in front often helps.
  • Be careful what you type, you can easily break your system with this command. (But don’t worry, we can reinstall.)

Package manager

  • The package manager is a handy way to install software in linux
  • “apt-cache search _keyword_” to find software. (Replace “_keyword_” with what you want to find, e.g. “apt-cache search arduino“.)
  • “sudo apt-get install _packagename_” to install the software by name. (Replace “_packagename_” with what you want to install.)
  • “sudo apt-get update” to update package lists.
  • “sudo apt-get upgrade” to upgrade all software to latest version.

USB hard/flash drive usage (FAT format)

  • It’s a good idea to connect your USB device before starting up the raspberry pi!
  • Easiest way to get USB drives to mount is running the desktop at boot. See command raspi-config. They will mount under the folder /media/.
  • Starting the desktop might slow you down if you don’t need it. Another possibility is manual mounting:

    1. Run command “sudo ls /dev/sd*” to find your device, it should be either /dev/sda1 or /dev/sda2.
    2. Run “sudo mkdir /mnt/usb” to create a mounting point for your device.
    3. Run “sudo mount -t vfat /dev/sda* /mnt/usb” (replace /dev/sda* with your device from next step).
    4. Your hard drive should now be in the location /mnt/usb.

Adding analog inputs with MCP3208 Analog-digital converter (ADC)

  • If we want to loose the Arduino in our setup, we can communicate directly with an ADC from the Raspberry pi.
  • To connect, you can follow Adafruit’s tutorial.
  • To connect the analog readings to something else than python, we need for example OSC messaging. Ask the teacher if you are unsure about how to work with OSC.