Make a loop in Ruby with peripherical that detects rfid

Question

so I'm trying with my raspberry to do a program that reads rfid cards in Ruby.

#!/usr/bin/env ruby

require 'mfrc522'




class Rfid
    def read_uid
        r = MFRC522.new
        r.picc_request(MFRC522::PICC_REQA)
        begin
            uid, sak = r.picc_select
            puts "El seu identificador es: "
            puts "%02x%02x%02x%02x" % uid
        rescue
            retry
        end
        return uid
    end
end


if __FILE__ == $0


rf = Rfid.new
uid=rf.read_uid


end

The problem is that if my card is not over the rfid when i execute the program it gets a CommunicationError. I am trying to do a loop so that if it doesn't detect the card it keeps trying but it doesn't work. Any ideas??

Answer 1

The basic problem you faced with is that begin .. end is not a loop. You can read more about ruby loops here for example

I think it should looks like this:

class Rfid
  def read_uid
    r = MFRC522.new
    loop do
      r.picc_request(MFRC522::PICC_REQA)
      uid, sak = r.picc_select
      
      puts "El seu identificador es: "
      puts "%02x%02x%02x%02x" % uid

      break uid if uid
    rescue
      redo
    end
  end
end

rescue - is to retry when you get any error raised

break - to quit from looping

I also should to note that using rescue without specific error class - it's bad practice because it might rescue any error even if it's just a typo in code.

In your case it might be like:

class Rfid
  def read_uid
    r = MFRC522.new
    loop do
      .... 
      break uid if uid
    rescue CommunicationError
      redo
    end
  end
end