Resistor

Resistor is a gem for the resistor unit.
For more details, please see http://qiita.com/seinosuke/items/d527b0e591d6d69c7471.

Installation

Add this line to your application's Gemfile:

gem 'resistor'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install resistor

Usage

Resistor Color Code Converter

You can calculate a resistance value from a color code. The contrary is possible.
Resistor::ColorCode.encode Converts a resistance value to a color code.
Resistor::ColorCode.decode Converts a color code to a resistance value.

require 'resistor'

Resistor::ColorCode.encode(4700)
# => [:yellow, :purple, :red, :gold]
Resistor::ColorCode.decode([:yellow, :purple, :red, :gold])
# => 4700.0

Combined Resistor Calculator

You can calculate a combined resistance value.
Resistor::BasicReisistor#+ Calculates a series combined resistance value.
Resistor::BasicReisistor#/ Calculates a parallel combined resistance value.

Resistor.new is an alias for Resistor::BasicResistor.new

require 'resistor'

r1 = Resistor.new(20)
r2 = Resistor.new(30)
r3 = Resistor.new(4)
r4 = Resistor.new(8)

#    --[r1]--          --[r4]--
# --|        |--[r3]--|        |--
#    --[r2]--          --[r4]--
r5 = (r1 / r2) + r3 + (r4 / r4)
r5.ohm # => 20.0

5-Band Color Code

Selects a number of color bands. By dafault, the number is 4.
Resistor::Options.set_band_number Sets a combination of options that is usually used.

require 'resistor'

Resistor::Options.set_band_number 5
Resistor.new(976)
# => #<Resistor::BasicResistor:0x0000000295fb58 @ohm=976.0, @code=[:white, :purple, :blue, :black, :brown], @tolerance=1.0>
Resistor::ColorCode.encode(100)
# => [:brown, :black, :black, :black, :brown]

Resistor::Options.set_band_number 4
Resistor.new(4700)
# => #<Resistor::BasicResistor:0x0000000295ee10 @ohm=4700.0, @code=[:yellow, :purple, :red, :gold], @tolerance=5.0>
Resistor::ColorCode.encode(100)
# => [:brown, :black, :brown, :gold]

E Series

Resistor::BasicReisistor#e12? Whether or not the resistance value is the E12 series.
Resistor::BasicReisistor#e24? Whether or not the resistance value is the E24 series.
Resistor::BasicReisistor#e48? Whether or not the resistance value is the E48 series.
Resistor::BasicReisistor#e96? Whether or not the resistance value is the E96 series.
#48? and #96? always return false if the number of bands is 4.

require 'resistor'

r1 = Resistor.new(4700)
r2 = Resistor.new(62)

r1.e12? # => true
r1.e24? # => true
r2.e12? # => false
r2.e24? # => true

Resistor::Options.set_band_number 5

r3 = Resistor.new(105)
r4 = Resistor.new(4.99)

r3.e48? # => true
r3.e96? # => true
r4.e48? # => false
r4.e96? # => true