Standalone microcontroller trouble with RFID recognition

I have an RFID controller that I connect to my Arduino in order to read RFID cards. In my sketch I have several RFID tags saved in an array. All I want to do is have an LED light up when a swiped RFID cards tag matches one of the saved tags. I got this working, so then I decided to move the Arduino microcontroller to a breadboard via this tutorial: Arduino - Setting up an Arduino on a breadboard

However, now when I connect the RFID controller and swipe a few cards, none of them are recognized. I know that the cards are being read since I tried commenting out the lines that do the check and assume that all cards are recognizable and the LED lights up when reading the cards. I just don't know why it would work on the Arduino, but not on the breadboard. As far as I understand, whatever is being read with Serial.Read() is not matching any of the stored values, which is weird.

Any help would be greatly appreciated. Thanks!

Cannot you serial print , or something similar, so you can see the data coming from the Rfid reader.

Breadboard often gives problems with poor connections, partic things like crystals and their caps which have very thin leads and do not make good connections.
Soldering those parts together with some thicker wires to plug in to the breadboard often help.

Wonder what the advantage of repilcating your Uno on the breadboard is ? certainly costs more ..

I tried to serial print to see what values are coming from the RFID reader, but the values printing to the serial monitor are junk. I'm connecting the RX and TX from the microcontroller on the breadboard to the Arduino RX and TX. Then connecting the Arduino to the computer for power. Even when I try printing a simple string it comes out as unreadable junk. I'm sure there's something that I'm doing wrong, I'm new to this. I've tried changing the baud rate too.

The advantage is that I want to fit the circuitry in a smaller space for a game I'm making. And I need to make half a dozen of them. It also costs a lot less than an Arduino itself.

First get serial working between the standalone arduino and a serial adapter.

Is the board running at the speed you think it is?
Upload blink to it and see if it blinks at the right speed. If you're uploading via ISP, it's possible to upload without having set the fuses (by using burn bootloader), so the board would be running at 1mhz off internal oscillator, when you're uploading code compiled for 16mhz.

The tutorial you are using omits a critical component - you need to include a 0.1uf ceramic capacitor between Vcc and Gnd, and between AVcc and Gnd right next to the chip (I've had to throw out boards I had custom made because I put this cap too far away). Without the decoupling capacitors, the chip will not function reliably (it may work sometimes - that's how bogus tutorials like this persist).

As long as you specify the baud rate in the set up and set your Serial monitir to the same rate , it should work.

void setup() {
  // initialize serial:
  Serial.begin(9600);

...

  Serial.println("Hello");

Like DrAzzy suggested the first thing I need to solve is printing out the values being read through the Serial. I've followed several tutorials, but none of them seem to work for me. I keep getting a problem uploading to the board when the microcontroller is on the breadboard. From the shield to the microcontroller on the breadboard I connect the Reset, Ground, 5V, and Rx to Rx, and Tx to Tx. The error I'm getting is: avrdude: stk500_recv(): programmer is not responding. Any help for this would be appreciated.

The problem was I was using 20 MHz crystal and I needed to use a 16 MHz crystal. All problems fixed now. Thanks for everyone's help!