Shifting an 74HC595 (595) 8-bit shift register on a Raspberry Pi using Pi Piper

shifter.rb

#!/usr/bin/env ruby
# To get pi_piper on Raspbian:
#
# apt-get install ruby-dev
# gem install pi_piper --no-ri --no-rdoc
# gem install rb-inotify --no-ri --no-rdoc
#
# These pins work but send a weird signal at boot.
#
# This script will take a string array and output it to the outputs on the shift register
#
#    "0" = OFF
#
#    "1" = ON
#
# The pins on the shift register should be set up as follows on the RPi
# (Shift Register 74HC595)
#
#   Ds   <-> GPIO 24
#
#   SHCP <-> GPIO 4
#
#   STCP <-> GPIO 25
#
#   !MR  <-> Vcc (+5V)
#   !OE  <-> Gnd

require 'pi_piper'
require 'rb-inotify'

NUMBER_OF_OUTPUTS = 16

PINS = {
  data:  PiPiper::Pin.new(pin: 24, direction: :out),
  clock: PiPiper::Pin.new(pin: 4, direction: :out),
  latch: PiPiper::Pin.new(pin: 25, direction: :out),
}

def shift(key)
  PINS[key].on
  PINS[key].off
end

def reset
  PINS.values.each{|pin| pin.off }
end

def watch_shift_file
  shift_state_filename = '/etc/shifter/shift_state.txt'
  send_bits File.open(shift_state_filename, 'r'){|f| f.read }
  
  notifier = INotify::Notifier.new
  notifier.watch(shift_state_filename, :modify) do
    send_bits File.open(shift_state_filename, 'r'){|f| f.read }
  end
  notifier.run
end

def send_bits(data)
  reset
  NUMBER_OF_OUTPUTS.times do |byte|
    PINS[:data].on if data[byte] == "1"
    shift :clock
    PINS[:data].off
  end
  shift :latch
end

if ARGV[0]
  send_bits ARGV[0]
else
  watch_shift_file
end