Binary convert to string in Ruby
BinaryChar is a class with one method. You continually change the state of the object so you can call the method with the right "argument". That's not what classes are for, but module functions or class methods. I rewrote the code twice: once using a class in the right way and once using a module function (or class method).

with a class

class BinaryChar
  def initialize(string)
    @binary = string.scan(/.{1,8}/).map do |character|
      character.to_i(2).chr
    end
  end

  def to_s
    @binary.join
  end
end

loop do
  print "Enter string: "
  bc = BinaryChar.new(gets)

  puts bc # to_s is called automatically by puts.
end


with a module function

module Binary
  def self.to_binary(string)
    binary = string.scan(/.{1,8}/).map do |character|
      character.to_i(2).chr
    end

    binary.join
  end
end

loop do
  print "Enter string: "

  puts Binary.to_binary
end


A couple of minor nitpicks:


In ruby the convention is to use snake_case for anything but ClassNames and CONSTANTS.
When you get input from stdin (gets) a newline is appended to it ("\n"). In most cases you want to strip the newline of using String#chomp.
Accessor methods can look just like variable assignments: bc.binary_string = speak.
Conversion methods are usually named to_&lt;something&gt;. To convert to a String, for example, most classes implement a to_s method.