Raspberry Pi newbie

I just got a Raspberry Pi for my birthday. How do I make it work and do things?

Nice daemons to start after boot

• sudo ~pi/Desktop/Raspberry-Pi-newbie/repeating_camera.py ceiling.jpg &

• python3 check_wifi.py &

• cd ../Mulder-quote-generator; python -u bot.py > log.txt &; mess w pid.txt

• cd ../sysadmin-webapp; nohup ./webapp.py &

Achievements unlocked

In the category of pure blinkenlight demos:

• Represent STDIN on LEDs, as either ASCII binary or on a seven-segment display. We use the text of Pride and Prejudice. Example: cat pride_and_prejudice.txt | sudo ./cat_leds.py &
• Count off the seconds in binary using LEDs.
• Fade an LED in/out by varying the duty cycle.
• Randomly varying LED bar graph meter.
• Raspberry Pi plays pong with itself using LEDs.
• Blink a single LED in rhythm of some programmed songs.
• Make a strobe light LED.
• Make a line of LEDs scan back and forth at random rates.

In the category of multimedia:

• Use an LED as a light sensor.
• Make musical square wave beeps on an old headphone that I cut up, without using a digital-analog converter .
• Record the rhythm of switch presses and play the rhythm back on an LED.
• Low light camera photos
• Temperature sensor controls LEDs.
• Time lapse photography
• Motion detection triggered camera
• Drive an LCD. cat pride_and_prejudice.txt | ./lcd.py
• Stock quotes to LCD
• Multiple temperature sensors to SQLite database & analytics

Note: to run, many of these require sudo ./pong.py or equivalent. Ones that don't require sudo would include ascii.py and seven_segment.py, which require STDIN piped input. See above.

Example temperature graphs

Wiring

1. Note to self. Inside my Pi box, the red stripe on ribbon connects with the red stripe toward the corner. In other words, red stripe toward the little power-on LED, or toward the edge with the DISPLAY connector, away from the edge with the CAMERA connector. This was mostly obvious but not 100%.

2. The basic scheme is as follows. Canakit T connector pin 11 (labeled as "17" meaning GPIO 17) --> long leg of LED --> Short leg of LED --> 220 ohm --> GND (canakit T, pin 39)

3. Wiring multiple LEDs to the same common resistor & ground can cause some of them not to light. I hypothesize unequal voltages of the GPIO pins, and/or unequal internal resistances of the LEDs.

4. Pull up goes as follows: +3 --> 1k ohm --> GPIO. Also 1k ohm --> switch --> GND.

5. Temp sensor:

   • red --> 3V3
   • black --> GND
   • yellow --> GPIO 4
   • red --> 1k ohm --> yellow
   • Add dtoverlay=w1-gpio-pullup,gpiopin=4 to /boot/config.txt
   • sudo modprobe w1-gpio; sudo modprobe w1-therm

Shift register directly

• sudo modprobe i2c-dev
• i2cdetect 1
• sudo apt-get install python-smbus

LCD

• dtparam=i2c_arm=on to /boot/config.txt
• sudo modprobe i2c-dev
• sudo apt-get install i2c-tools
• i2cdetect 1
• sudo apt-get install lcdproc
• LCDd -c LCDd.conf &
• lcdproc -f -c lcdproc.conf

WiFi

TL;DR: wpa_supplicant.conf is rather hellish.

The default way that wpa_supplicant gets started is: /sbin/wpa_supplicant -s -B -P /var/run/wpa_supplicant.wlan0.pid -i wlan0 -D nl80211,wext -c /etc/wpa_supplicant/wpa_supplicant.conf

Here is a good way to watch what is going on: sudo wpa_supplicant -c /etc/wpa_supplicant/wpa_supplicant.conf -iwlan0 -d

wpa_gui & is helpful for clicking and watching and such.

Also consider watch tail -n 15 /var/log/syslog

Eventually when it worked [but merely manually], I just did: sudo wpa_supplicant -c /etc/wpa_supplicant/wpa_supplicant.conf -iwlan0 &

Check out file wpa_supplicant.conf in this repo for the code that worked. I think key_mgmt=WPA-PSK ends up getting auto-changed to CCMP or something, on my particular network.

To get it to work finally automatically on reboot, the issue was ap_scan=2 incompatibility with nl80211. Leaving off the forcing of nl80211 driver from the command line would work, but clearly that required manually starting wpa_supplicant, as it runs it "the default way" (see above) on reboot. So basically I had to read http://w1.fi/cgit/hostap/plain/wpa_supplicant/wpa_supplicant.conf which is different from my /usr/share/doc/wpa_supplicant/examples/wpa_supplicant.conf.gz file!! Key quote:

# Note: ap_scan=2 should not be used with the nl80211 driver interface (the
# current Linux interface). ap_scan=1 is optimized work working with nl80211.
# For finding networks using hidden SSID, scan_ssid=1 in the network block can
# be used with nl80211.

Play with my other repos

• curl -O https://pypi.python.org/packages/source/p/pycrypto/pycrypto-2.6.1.tar.gz

• sudo apt-get update

• sudo apt-get install python-dev

• sudo python setup.py build

• sudo python setup.py install

• python setup.py test

• curl -O 'https://pypi.python.org/packages/source/g/gensafeprime/gensafeprime-1.5.tar.gz'

• etc