PIN Generator that can generate single PINs or an Array with a specified count of unique PINs

pin_generator.rb

class PinGenerator
  class << self
    def single(length)
      chars = [('A'..'Z'), ('0'..'9')].map(&:to_a).flatten
      chars.delete "O"
      chars.delete "0"
      chars.delete "I"
      result = ""
      prev_char = ""
      while result.length < length do
        char = chars[Kernel.rand(chars.length)]
        next if (prev_char == "B" and char == "8") or (prev_char == "8" and char == "B") or (prev_char == "V" and char == "V")
        result << char
        prev_char = char
      end
      result
    end

    def multiple(length, count)
      pins = []
      while pins.length < count
        count_left = count - pins.length
        pins += (0...count_left).map { single(length) }
        pins.uniq!
      end
      pins
    end
  end
end

It would be nice to exclude a set of PINs by specifying an optional argument (except/exclude)