Saturday, October 24, 2015

One minute tutorial: Getting started with a fresh NodeMCU ESP8266 (direct from eBay)

The NodeMCU / ESP8266 is a ridiculously cheap ($2) micro-controller that can talk to an 802.11N wireless network. This device is the herald of the "Internet of Things."

If you buy one on eBay, chances are it will NOT be flashed with NodeMCU firmware (it speaks Lua). This understandably confused the crap out of me. So, this serves as a guide to those running Manjaro (Arch) Linux:

  1. Download NodeMCU firmware
    "integer" versions will NOT understand floating point arithmetic, but save on system resources.
  2. Install minicom
    pacman -Ss minicom
  3. Install esptool from the AUR:
    yaourt esptool-git
  4. Make sure your Linux box recognizes the device
    tail -f /var/log/messages.log
  5. Plug in the NodeMCU device. You should see:
    kernel: usb whatever: ch341-uart converter now attached to ttyUSBX

    ch341-uart converter detected

    If this didn't happen, you cannot proceed and must troubleshoot.
  6. Flash the firmware. Make sure you have permission to read and write to the device in the command below. When in doubt, run as root: --port /dev/ttyUSBX write_flash 0x00000 nodemcu_whatever.bin
    X corresponds to the device from the log file above, and
    nodemcu_whatever.bin corresponds to the firmware file in step 1.
  7. Unplug the USB cable after the flash command from the previous step is completed, and plug it back in.
  8. Fire up minicom, and talk to the board at 9600 baud:
    minicom -D /dev/ttyUSBX -b 9600
  9. Press the "enter" key a few times. In response, you should see:
  10. Try "hello world":
    > print ("hello world")
    hello world

  11. Now you can configure wireless:
    > wifi.setmode(wifi.STATION)

    > wifi.sta.config("SSID", "PASSWORD")

    > ip, nm, gw=wifi.sta.getip()

    > print (ip, nm, gw)
    this   is   amazing
  12. Do some interesting things!

Wednesday, October 7, 2015

How to tell the difference between crocodiles and alligators

Such things are important when you have young children, so I authored a rhyme (with help of a friend on Facebook):
Crocs always show both rows of teeth
And swim in salty sea.
When gators smile, you see a "U,"
With crocs, you see a "V"

With dotted snout in muddy swamp,
the Gator lies happily.
Crocs, with spots from head to toe,
Live life... estuarily.

Friday, October 2, 2015

Extracting structured data (in a table) from HTML5 using BeautifulSoup / Python

I recently ripped a CD that was unknown to my CDDB server. I found a web page that contained a track list, but found it very cumbersome to copy and paste the information due to the formatting of the web page.

Consequently, I opened up the page using the Firefox DOM inspector, and noticed that each title was associated with HTML class 'title'. Surely, the data element of interest could be extracted using some higher-level language!

I elected to do some research and discovered that I could solve this problem, easily, using Python 2.7 and BeautifulSoup.

After some research (having never used BeautifulSoup before), this is the unbelievably simple script that I came up with:

from requests import get
from bs4 import BeautifulSoup
url = ''
htmlString = get(url).text
html = BeautifulSoup(htmlString, 'html5lib')
tags = html.find_all('div', {'class':'title'})
text = [t.get_text() for t in tags]
print str(len(text)) + ' items matched:\n'
# join(j.split()) is a quick hack to remove excess whitespace
for i,j in enumerate(text): print ' '.join(j.split())

WOW! Clearly, this is a useful library.