Trouble converting serial port data to hex, data is from an RFID reader

Question

I am trying to attain data from an RFID reader I have attached to a serial port. The data is coming through as jumbled characters, which I have to convert to hex. I am getting an error trying to convert it to hex, when I do this:

puts "%02X" % key

I get this error: '%' : invalid value for Integer(): "\xE2\x10......"etc

It is almost converting it right as the "\xE2\x10..." etc is close to what it should be outputting, it should be 00 00 E2 00 10... etc. I'm not sure if there is another way to convert it to hex, I've also tried:

key.to_i.to_s(16)

and

key.hex

But both produce 0 as the output, which isn't correct. When I try to convert it to just an integer it converts it to a 0, I'm not sure why.

Here is the full code if that helps, most of it is taken from an example on the net:

require "serialport"
class RfidReader
 attr_accessor :key

 def initialize(port)
   port_str = "COM7"
   baud_rate = 9600
   data_bits = 8
   stop_bits = 1
   parity = SerialPort::NONE
   @sp = SerialPort.new(port_str, baud_rate, data_bits, stop_bits, parity)
   @key_parts = []
   @key_limit = 16 # number of slots in the RFID card.
   while true do
     main
   end
   @sp.close
 end

 def key_detected?
   @key_parts << @sp.getc
   if @key_parts.size >= @key_limit
     self.key = @key_parts.join()
     @key_parts = []
     true
   else
     false
   end
 end

 def main
   if key_detected?

    self.key.gsub!(/\0/, '')
    #puts self.key.hex
    #puts self.key.to_i.to_s(16)
    puts "%02X" % key
    #puts key



   end
 end
end

RfidReader.new("COM7")

Answer 1

What you get is a string containing the bytestream from your RFID reader. Use String#unpack¹ to convert the byte string to actual bytes (numbers).

random_bytes_from_reader = "\xE2\x10\x42\x23\xA9"
random_bytes_from_reader.unpack('C*') # assume we have unsigned chars
#=> [226, 16, 66, 35, 169]

You already figured out how to display them as hex strings with number.to_s(16).

¹ Read the documentation! The param of unpack depends on the specification of your RFID reader. 'C*' was just a guess on my part.