Background Knowledge Probe

• Which of your daily-use mechanical tools, if any, have attached digital electronic components? Think about this broadly, including your car or kitchen appliances, for example.
• Which of these digital electronics are microcomputers? Microcontrollers? A combination of the two?
• In what ways is the design and use of the digital component prioritized over the mechanical? The mechanical over the digital?
• In what ways are your daily-use tools, mechanical and digital, prioritized over the person? In what ways are your daily-use tools first and foremost person-centered?

Data Communications Between Devices

The Raspberry Pi, like many microcomputers and microcontrollers, provides pins to which you can attach transmit and receive wires to connect with personal computers. In this way, even if there is no network or keyboard, mouse, and monitor to provide access to one of these devices, a simple USB to serial cable can be used to configure, diagnose, or perform regular tasks on it. Many operating systems, such as the Raspberry Pi OS, also provide a control window to output and input text from and to the device through this serial interface.

A note on the technical terms Master and Slave:

• Historically, the technologists who developed these data communication tools used the term Master to indicate the controlling device and Slave to indicate devices being controlled by that device. I follow the lead of Python developers who, moving forward, are using the terms Parent and Worker, respectively. These changes within Python coding were made in November 2018, after heated discussion launched by a change request submitted in September 2018 by Victor Stinner, a developer with the software company Red Hat.^[1]
• Other programming languages have implemented similar changes. Drupal uses the term replica to replace slave and primary to replace master. As another example, Django has moved to follower and leader.
• The terms still largely used within engineering and computer science remain slave and master. In discussions regarding these change requests, many argued that these common terms are used to refer to the operation of technology independent of, or at the direction of, another technology with no reference to human slavery. They argue that because there is no common replacement that could easily be made given the existing labels on electronics and in code back many decades, it is important to stay with the stock terminology.
• As you read through this document and look at abbreviations listed on your electronics and in code, note that sometimes the listed abbreviations — for instance MISO, below — do not align with written descriptions in this text — Parent In/Worker Out.

Communications between devices takes many shapes and forms using a range of protocols. Three of the most commonly used are:

• I2C (Inter-Integrated Circuit and pronounced I-squared-C) was developed in the early 1980s and is widely used to connect lower-speed peripheral integrated circuits to microprocessors and microcomputers using the bus topology (think of a physical bus you ride to travel with others between locations). It is designed to work over relatively short distances, and allows multiple “worker” integrated circuits to communicate with one or more “parent” integrated circuits. I2C only requires two wires and can support up to 1008 worker devices. It can also support multiple parent devices, allowing for more than one parent to communicate with all devices on the bus.
• SPI (Serial Peripheral Interface) is another widely used bus topology protocol used to send data between peripherals and microcontrollers/microcomputers. What is unique about SPI is that it uses a serial clock in addition to a MOSI (parent out, worker in) data line and a MISO (parent in, worker out) data line. The serial clock’s oscillating signal allows for data communications to occur synchronously. As with I2C, multiple workers can connect to a single parent. To accomplish this, a fourth line, SS or Worker Select, alerts a particular worker that it should wake up and send and/or receive data, as well as to detect that multiple workers are present.
• UART (Universal Asynchronous Receive Transmit) interfaces: UART is actually a microprocessor with a package of integrated circuits on a printed circuit board, along with program logic, and is used to attach serial devices to a computer. This allows the computer and attached devices to “talk” and exchange data. There is a range of USB (Universal Serial Bus) TTL (Transistor Transistor Logic) serial cables used to provide connections between USB and serial UART devices. For our purposes, UART is the simplest and a very effective strategy for basic work in the console window of the Raspberry Pi using a personal computer.

Exercise: The Circuit Playground Express Meets the Raspberry Pi

In the first three technical session chapters, we’ve explored MakeCode and configured our Circuit Playground Express microcontroller, eventually working to create our own functions. In this session, we’ll bring together the microcontroller and the Raspberry Pi microcomputer to allow us to use the “trumpet valves” to play selected counterstories saved on the Raspberry Pi. To do this, we’ll use the UART serial communications pins found on the Circuit Playground Express and the UART Python extension on the Raspberry Pi to transmit valve press sensor data from the Circuit Playground Express to the Raspberry Pi, and to then assess this data to choose which of the available MP3 counterstories to play using the audio output of the Raspberry Pi.

We’ll accomplish this in three steps:

STEP 1: Set up the Raspberry Pi to store and play counterstories using the VLC free and open-source, cross-platform multimedia player. This may have already been done previously, as it is an exercise within the Orange Unit.

STEP 2: Set up your Circuit Playground Express. The Toolbox Trumpet will now be expanded to use components of the MakeCode Serial UART Communications Extension to transfer capacitive touch and momentary switch data to the Raspberry Pi to play counterstories based on sensor inputs.

STEP 3: Use the Toolbox Trumpet to play short counterstories (no momentary switches pressed), introductions to the counterstories (left switch pressed), and extended counterstories (right switch pressed). A simple Python-based program has been included to test out the Circuit Playground Express, the USB to TTL serial cable, and the Raspberry Pi as a media center.

To work through these steps, it is now time to bring together the technical activities with the social activities. Work through these in pairs. Or perhaps before doing these activities in pairs, join in a community of practice to consider ways to approach this within a diversity of community cultural wealths that are present. This is to be a work not of doing alone, but of being present within the space, with the people in this room. The book Emergent Strategy highlights several principles relevant in considering technical activities within a community of practice, and a community of practice as something that is completed through being present rather than as driven-doing acts. These include:

There is always enough time for the right work.

There is a conversation in the room that only these people at this moment can have. Find it. Never a failure, always a lesson.

brown, adrienne maree. Emergent Strategy (p. 44). AK Press. Kindle Edition.

How can the following be accomplished in such a way that the community cultural wealth of all present are advanced as part of taking on these activities collaboratively?

How can this be part of a larger task of advancing a counterstory regarding sociotechnical innovation-in-use?

pi@raspberrypi:~ $ mkdir cstories
pi@raspberrypi:~ $ cd cstories
pi@raspberrypi:~/cstories $ ls
  cStory1.mp3  cStory1-extended.mp3   cStory1-intro.mp3
pi@raspberrypi:~/cstories $

pi@raspberrypi:~ $ cd cstories
pi@raspberrypi:~/cstories $ cvlc cStory1.mp3 vlc://quit

Step 3: Use the Toolbox Trumpet to Play Your MP3 Files

Now let’s connect up your Raspberry Pi to your Circuit Playground Express using a USB to TTL cable and some male to alligator clips. You will now provide power to the Circuit Playground Express directly from the Raspberry Pi via the USB port, by connecting the red TTL wire to the VOUT on the Circuit Playground Express using a fourth male to alligator clip wire. In this way, one power source directly attached to the Raspberry Pi is all that is needed to run the whole digital Little Free Library!

NOTE: Do not connect the red wire to VOUT power if your Circuit Playground Express is getting power from another source, such as your laptop.^[3]

 

1. Use three or four male to alligator clip wires to connect the TTL side of a TTL/USB Serial Cable to the Circuit Playground Express microcontroller:
   • Black wire to ground (GND)
   • Red wire to power (VOUT) (do NOT connect if Circuit Playground Express is getting power from another source, such as your laptop)
   • White wire to transmit (TX)
   • Green wire to receive (RX)
2. Plug the USB side of the second serial cable to one of the four USB ports on the Raspberry Pi. Any one of these should work OK. You should see the Circuit Playground Express green power light go on. If not, a few tests can include:
   • Confirm that there is power on the Raspberry Pi and that it is not in the boot-up phase.
   • Check to see if the cable USB is fully pressed into the USB port of the Raspberry Pi.
   • Try using a different USB port on the Raspberry Pi.
   • Confirm that the GND and VOUT pins are properly connected to the red and black wires on the TTL/USB serial cable.
3. From a web browser, enter: https://go.illinois.edu/cstories
   • Take a glance at the code, but most importantly, right-click in the window to download the program as cstories.py (not as cstories.txt as automatically listed).
     • Make sure to move cstories.py to the /home/pi/Code/Python directory,
   • You can download the Python code in several ways:
     • Directly from the Raspberry Pi’s Graphical User Interface, using a web browser on the Raspberry Pi.
     • By downloading it to your laptop’s cstories folder, and then transferring the file using the USB to TTL serial console connection.
     • By downloading it to your laptop’s cstories folder, and then transferring the file using SSH/SCP (secure shell and secure copy) in a terminal (Mac) or PowerShell (Windows 10) window. For this approach, first identify the IP address of your Raspberry Pi. Jump to Network Troubleshooting for instructions. Visit Introducing the Unix Command Line for details on using SSH/SCP.
   • The cstories.py code does an import of two libraries with supplemental code: one library for serial communications, which we’ll use to communicate with the tty to UART cable, and the second for the VLC library of commands. The serial library comes pre-installed, but we now need to install the VLC library using pip3:

     pi@raspberrypi:~ $pip3 install python-vlc

   • If you have more than one cstory with intro, main, and extended files, open cstories.py with Thonny or the graphical editor mousepad to edit the Python code. Change the variable “numStories” from 1 to the number of cstories now on the Raspberry Pi.

     pi@raspberrypi:~/cstories $ mousepad /home/pi/Code/Python/cstories.py

     • Navigate to the row that starts “numStories.” Navigate to the number 1, and change it to the number of stories you have transferred to /home/pi/cstories.
     • To save in mousepad, click on the Save button and then close the window.
     • To save in Thonny, click on the Save button.
4. Test it all out in either Thonny or the Terminal:
   • In Thonny, you can click on the Run icon. Look in the Shell window in the bottom half of Thonny to see the output that would normally go to a terminal window.
   • In the terminal window, type the following, and then touch the different Toolbox Trumpet valves to see if you can hear a story being read to you:

     pi@raspberrypi:~/cstories $ python3 ~/Code/Python/cstories.py

     • To exit the Python command output, provide a keyboard interrupt by holding down the Control (that is, CTRL or ^) key, and then hitting the “c” key.

FAIL FORWARD TIPS:

• Sometimes, the connection of the USB/TTL Serial Cable from the Circuit Playground Express to the Raspberry Pi may have changed. In the terminal window on the Raspberry Pi, type:

pi@raspberrypi:~ $ ls /dev/ttyUSB*

Note the result. If nothing is listed, then the USB/TTL Serial Cable may not be connected. Otherwise, compare the returned value(s) with the one listed in the “uart” variable within the cstories.py code. The best way to do this is by using nano. If the value returned from the “ls” command is different from that listed in “uart = serial.Serial,” then change the number accordingly in the Python code, save, and retest.

• The cstories.py code does not have a way to cut short the playing of a selected story. The VLC player also can handle the playing of multiple stories by default. Stop the cstories.py prototype to end the telling of one story early, and restart the Python program again to start a new story with the A1, A2, and A4 key combinations, along with Button A or Button B as needed.

Wrap Up

The primary objective of the Blue Unit is to bring together our microcontroller and microcomputer systems as a means of sharing data between devices, thereby creating a basic physical network. That is, we’ve worked to create a digital networked information system. Together, we can advance a range of technical skills in addition to a number of cognitive and socio-emotional skills to help your community of practice use a growth mindset to build these multi-layered systems.

Do Something New!

Entering into this final stage putting together a Raspberry Pi Counterstory Little Free Library, there have been a range of expertise and community cultural wealth brought into the activities as a team. For some, strengths may especially be in the computer programming front. For others, you may bring with you a background within issues of social justice. Consider also the diverse lived experiences, cultures, and other influences that have shaped your selection of a story that you have turned into one you would tell through this sociotechnical system.

• How might you now work together to create a series of seven stories selected to especially speak to a special audience?
• Which would play with A1, that is cStory1?
  • A2, that is cStory2?
  • A1 + A2, that is cStory3?
  • A4, that is cStory4??
  • A1 + A4, that is cStory5?
  • A2 + A4, that is cStory6?
  • A1 + A2 + A4, that is cStory7?
• What would play if someone simultaneously pressed both Button A & B? How might this be used as a secret “Easter Egg” part of the story (Easter Egg is a gaming metaphor for a hidden aspect).

The exercises have stepped you through the sharing of this story through integration of the Circuit Playground Express UF2 code and the Raspberry Pi Python code. The Python code itself provides opportunities to share between 1 and 7 different stories headless, that is without a monitor. But as we learned in Orange Unit 4C: Getting Started with the Raspberry Pi, Python also has a library file to work with a the PiOLED we’ve been using to identify the IP address assigned to the Raspberry Pi.

• How might you reuse the PiOLED to instead indicate a list of stories and to share which story is currently being played?
• Are there ways we could use a small, low-powered monitor attached to the Raspberry as part of a portable Little Free Library to indicate a list of stories and to share which story is currently being played?

As you explore this Do Something New! be sure to use the various strengths of your team, and seek to bring in other expertise as possible, to investigate and prototype these possibilities of a sociotechnical system to share seven strategically selected critical social justice stories within a person-oriented social perspective.

Comprehension Check

Now would be a great time to revisit the lesson plan listed in “Valued, Inclusive Information and Computing Technology Experiences.” Spend some extended time with your Professional Journal Reflections this week, especially responding to the probes at the end of that session. As you reflect, bring our activities to date into conversation with the capability approach and inclusive computational thinking frameworks brought forward in this session.

1. In what ways might the toolbox trumpet and Raspberry Pi counterstories serve as a resource advancing agency? A capability?
2. In what ways might the toolbox trumpet and Raspberry Pi counterstories serve as an information system problematically disrupting valued beings and doings of individuals and communities?
3. In what ways might the toolbox trumpet and Raspberry Pi counterstories be designed for designers, that is, for the innovators-in-use who adapt this to their own functionings? In what ways might it have been designed differently leading to this point?