Kegmotron Lunch and Learn

What's a keg motron?

A wireless scale that the keg sits on.
Measures the weight of the beer.
Not overly accurate.

Demo

devmotron is there beer?
charts

Pictures

How Does it fit togeather?

      +
      |=~
    __|___
   { keg  }
   {______}
   {      }
   {______}
  ^~~^
  (fsr)
   |
   |
   ------\
   | xbee ] ~~UDP~~> +xbee_hex.rb+
   ------/                |
                          V
                +campfire_notifier.rb+
                   └- ~~HTTP~~> +hubot-kegmotron.coffee+ -> campfire
                   |
                   └- keg-log.dat
                       |
                       V
                  +keg-log.ru+

Electronics 101.

   1kΩ resistor
      |       fsr (variable)
      |       |
     ^^^^   ^~~~^
     |  \  |    |
  (+)║    \║    ║(gnd)
     ------------\
     |1    4    9 \
     |   (ADC)     ]
     |xbee        /
     ------------/

pin 1 is always 3.3v
pin 9 is always 0v
pin 4 voltage is the ratio of 1kΩ to the fsr resistance

Show some code you are proud of.

Show some code you hate.

Why I hate Ruby (Appendix 1):

Strings are not real IO, do not use them as buffers.

rd, wr  = IO.pipe
spawn "./xbee-hex.rb -p -c", out: wr

puts "[Setting up Xbee Read Pipe]"
rd.each_line do |status_update|
  # do something each time there's a \n on stdout
end

Ok, Take a file and turn it into stdin. Usefull when you want to give the file a generic name inside the program (this_plotter):

#!/usr/bin/env gnuplot
set term dumb
plot "/dev/stdin"

usage:

./this_plotter < file_of_the_moment.dat

Now, do it in Ruby:

spawn "this_plotter", out: in_memory_buffer, in: File.open("file_of_the_moment.dat")
puts in_memory_buffer
# No such object exists that can be used as `in_memory_buffer`
# Why can I not use a string, if strings are ruby's buffers?
# Why is there no IO::Buffer?
# Why is StringIO not an IO!?

Maybe a different way?

require 'open3'
stdout, _ = Open3.capture2 "this_plotter", stdin_data: File.read("file_of_the_moment.dat")

This is not great, we have to read the entire file!

~ Maybe that makes sense spawn is non-blocking capture2 is blocking ~

markjlorenz/kegmotron_LnL_outline.markdown