user29589: So I have an Arduino Uno and an MFRC-522 reader, using a breadboard I've wired it up according to the example sketch which is the mfrc522 DumpInfo sketch.
/*Typical pin layout used:
 * 
 *             MFRC522      Arduino 
 *             Reader/PCD   Uno/101
 * Signal      Pin          Pin     
 * -------------------------------
 * RST/Reset   RST          9          
 * SPI SS      SDA(SS)      10         
 * SPI MOSI    MOSI         11 / ICSP-4
 * SPI MISO    MISO         12 / ICSP-1
 * SPI SCK     SCK          13 / ICSP-3
 */

I've checked the wiring hundreds of times. The console shows 
    Firmware Version: 0x92 = v2.0
    Scan PICC to see UID, SAK, type, and data blocks...
but getting a card near the chip, will not scan or dump any info no other information appears on the serial monitor.
I've tried with mifare classic 1k  cards
a Nexus 6
and a Samsung Galaxy S7 
Edit: Everything
    /*
    * ------------------------------------------------------------------------------------------------------------------
    * Example sketch/program showing how to read data from a PICC to serial.
    * --------------------------------------------------------------------------------------------------------------------
    * This is a MFRC522 library example; for further details and other examples see: https://github.com/miguelbalboa/rfid
    * 
    * Example sketch/program showing how to read data from a PICC (that is: a RFID Tag or Card) using a MFRC522 based RFID
    * Reader on the Arduino SPI interface.
    * 
    * When the Arduino and the MFRC522 module are connected (see the pin layout below), load this sketch into Arduino IDE
    * then verify/compile and upload it. To see the output: use Tools, Serial Monitor of the IDE (hit Ctrl+Shft+M). When
    * you present a PICC (that is: a RFID Tag or Card) at reading distance of the MFRC522 Reader/PCD, the serial output
    * will show the ID/UID, type and any data blocks it can read. Note: you may see "Timeout in communication" messages
    * when removing the PICC from reading distance too early.
    * 
    * If your reader supports it, this sketch/program will read all the PICCs presented (that is: multiple tag reading).
 * So if you stack two or more PICCs on top of each other and present them to the reader, it will first output all
 * details of the first and then the next PICC. Note that this may take some time as all data blocks are dumped, so
 * keep the PICCs at reading distance until complete.
 * 
 * @license Released into the public domain.
 * 
 * Typical pin layout used:
 * -----------------------------------------------------------------------------------------
 *             MFRC522      Arduino       Arduino   Arduino    Arduino          Arduino
 *             Reader/PCD   Uno/101       Mega      Nano v3    Leonardo/Micro   Pro Micro
 * Signal      Pin          Pin           Pin       Pin        Pin              Pin
 * -----------------------------------------------------------------------------------------
 * RST/Reset   RST          9             5         D9         RESET/ICSP-5     RST
 * SPI SS      SDA(SS)      10            53        D10        10               10
 * SPI MOSI    MOSI         11 / ICSP-4   51        D11        ICSP-4           16
 * SPI MISO    MISO         12 / ICSP-1   50        D12        ICSP-1           14
 * SPI SCK     SCK          13 / ICSP-3   52        D13        ICSP-3           15
 */

#include <SPI.h>
#include <MFRC522.h>

#define RST_PIN         9          // Configurable, see typical pin layout above
#define SS_PIN          10         // Configurable, see typical pin layout above

MFRC522 mfrc522(SS_PIN, RST_PIN);  // Create MFRC522 instance

void setup() {
    Serial.begin(9600);     // Initialize serial communications with the PC
    while (!Serial);        // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
    SPI.begin();            // Init SPI bus
    mfrc522.PCD_Init();     // Init MFRC522
    mfrc522.PCD_DumpVersionToSerial();  // Show details of PCD - MFRC522 Card Reader details
    Serial.println(F("Scan PICC to see UID, SAK, type, and data blocks..."));
}

void loop() {
    // Look for new cards
    if ( ! mfrc522.PICC_IsNewCardPresent()) {
        return;
    }

    // Select one of the cards
    if ( ! mfrc522.PICC_ReadCardSerial()) {
        return;
    }

    // Dump debug info about the card; PICC_HaltA() is automatically called
    mfrc522.PICC_DumpToSerial(&(mfrc522.uid));
}

datasheet Nxp website /documents/data_sheet/MFRC522.pdf


user36862: your breadboard can be buggy. In addition, are you connected VCC to 3V or 5V?
As I remember, you need to connect it to 3V.

user40664: #include <SPI.h>
#include <MFRC522.h>

void setup() {
  Serial.begin(9600);
  SPI.begin();
  RFID.PCD_Init();      // MFRC522
}
#define SS_PIN 10
#define RST_PIN 9

MFRC522 RFID(SS_PIN, RST_PIN);

void loop() {
  if (!RFID.PICC_IsNewCardPresent() || !RFID.PICC_ReadCardSerial())
    return;

  String buffer;
  for (byte byte = 0 ; byte < RFID.uid.size ; byte++)
    buffer += String(RFID.uid.uidByte[byte] < 0x10 ? " 0" : " ") + String(RFID.uid.uidByte[byte], HEX);
  Serial.println("NUID: " + buffer);

  RFID.PICC_HaltA();
  RFID.PCD_StopCrypto1();
}


user48706: I had a similar problem. I used I2C to check if the board can see the reader. If I2C Bus doesn't detect your reader, then one of your soldering must be faulty... check with a meter and carefully re-solder the erring pin. 

user48909: I have several of this board with this condition. As I checked ,they all return the same thing as you send in SPI . I think all of them have hardware problem. Common thing for all of them is In past I supplied them with switching supply and I think this is why they got broken(this chip is very sensitive with supply voltage and YOU MUST NOT CONNECT THEM TO MORE THAN 3.3V EVEN FOR VERY SHORT TIME) . I highly recommend use of Linear regulator for them   

user67704: Same problem as above. Three card readers. Two worked. One didn't. All three  readers had two pins bridged on the reader chip. The bridged pins were close to the pin 1 corner. I left the bridge alone as all three readers had the same bridge and one of the pins did not have a trace to it. The faulty card reader also had two pins bridged with solder in a different location. Both pins had separate traces. I removed the solder bridge and the faulty card reader was no longer faulty.

user71475: I figured out that one get these kind of problems (reader get´s firmware version but can not read tags) are related to power consumption. I tried to power the reader with Heltec Lora 32 Dev board and it schowed exactly this behaviour. Now, connected to another 3,3V source everything works as it should :)

29589: <p>So I have an Arduino Uno and an MFRC-522 reader, using a breadboard I've wired it up according to the example sketch which is the mfrc522 DumpInfo sketch.</p>

<pre><code>/*Typical pin layout used:
 * 
 *             MFRC522      Arduino 
 *             Reader/PCD   Uno/101
 * Signal      Pin          Pin     
 * -------------------------------
 * RST/Reset   RST          9          
 * SPI SS      SDA(SS)      10         
 * SPI MOSI    MOSI         11 / ICSP-4
 * SPI MISO    MISO         12 / ICSP-1
 * SPI SCK     SCK          13 / ICSP-3
 */
</code></pre>

<p>I've checked the wiring hundreds of times. The console shows 
    Firmware Version: 0x92 = v2.0
    Scan PICC to see UID, SAK, type, and data blocks...</p>

<p>but getting a card near the chip, will not scan or dump any info no other information appears on the serial monitor.</p>

<p>I've tried with mifare classic 1k  cards
a Nexus 6
and a Samsung Galaxy S7 </p>

<p>Edit: Everything</p>

<pre><code>    /*
    * ------------------------------------------------------------------------------------------------------------------
    * Example sketch/program showing how to read data from a PICC to serial.
    * --------------------------------------------------------------------------------------------------------------------
    * This is a MFRC522 library example; for further details and other examples see: https://github.com/miguelbalboa/rfid
    * 
    * Example sketch/program showing how to read data from a PICC (that is: a RFID Tag or Card) using a MFRC522 based RFID
    * Reader on the Arduino SPI interface.
    * 
    * When the Arduino and the MFRC522 module are connected (see the pin layout below), load this sketch into Arduino IDE
    * then verify/compile and upload it. To see the output: use Tools, Serial Monitor of the IDE (hit Ctrl+Shft+M). When
    * you present a PICC (that is: a RFID Tag or Card) at reading distance of the MFRC522 Reader/PCD, the serial output
    * will show the ID/UID, type and any data blocks it can read. Note: you may see "Timeout in communication" messages
    * when removing the PICC from reading distance too early.
    * 
    * If your reader supports it, this sketch/program will read all the PICCs presented (that is: multiple tag reading).
 * So if you stack two or more PICCs on top of each other and present them to the reader, it will first output all
 * details of the first and then the next PICC. Note that this may take some time as all data blocks are dumped, so
 * keep the PICCs at reading distance until complete.
 * 
 * @license Released into the public domain.
 * 
 * Typical pin layout used:
 * -----------------------------------------------------------------------------------------
 *             MFRC522      Arduino       Arduino   Arduino    Arduino          Arduino
 *             Reader/PCD   Uno/101       Mega      Nano v3    Leonardo/Micro   Pro Micro
 * Signal      Pin          Pin           Pin       Pin        Pin              Pin
 * -----------------------------------------------------------------------------------------
 * RST/Reset   RST          9             5         D9         RESET/ICSP-5     RST
 * SPI SS      SDA(SS)      10            53        D10        10               10
 * SPI MOSI    MOSI         11 / ICSP-4   51        D11        ICSP-4           16
 * SPI MISO    MISO         12 / ICSP-1   50        D12        ICSP-1           14
 * SPI SCK     SCK          13 / ICSP-3   52        D13        ICSP-3           15
 */

#include &lt;SPI.h&gt;
#include &lt;MFRC522.h&gt;

#define RST_PIN         9          // Configurable, see typical pin layout above
#define SS_PIN          10         // Configurable, see typical pin layout above

MFRC522 mfrc522(SS_PIN, RST_PIN);  // Create MFRC522 instance

void setup() {
    Serial.begin(9600);     // Initialize serial communications with the PC
    while (!Serial);        // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
    SPI.begin();            // Init SPI bus
    mfrc522.PCD_Init();     // Init MFRC522
    mfrc522.PCD_DumpVersionToSerial();  // Show details of PCD - MFRC522 Card Reader details
    Serial.println(F("Scan PICC to see UID, SAK, type, and data blocks..."));
}

void loop() {
    // Look for new cards
    if ( ! mfrc522.PICC_IsNewCardPresent()) {
        return;
    }

    // Select one of the cards
    if ( ! mfrc522.PICC_ReadCardSerial()) {
        return;
    }

    // Dump debug info about the card; PICC_HaltA() is automatically called
    mfrc522.PICC_DumpToSerial(&amp;(mfrc522.uid));
}
</code></pre>

<p>datasheet Nxp website /documents/data_sheet/MFRC522.pdf</p>

<p><a href="https://i.stack.imgur.com/XGRw0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XGRw0.png" alt="When arduino starts and nothing changes when card is tapped"></a></p>
 36862: <p>your breadboard can be buggy. In addition, are you connected VCC to 3V or 5V?<br>
As I remember, you need to connect it to 3V.</p>
 40664: <pre><code>#include &lt;SPI.h&gt;
#include &lt;MFRC522.h&gt;

void setup() {
  Serial.begin(9600);
  SPI.begin();
  RFID.PCD_Init();      // MFRC522
}
#define SS_PIN 10
#define RST_PIN 9

MFRC522 RFID(SS_PIN, RST_PIN);

void loop() {
  if (!RFID.PICC_IsNewCardPresent() || !RFID.PICC_ReadCardSerial())
    return;

  String buffer;
  for (byte byte = 0 ; byte &lt; RFID.uid.size ; byte++)
    buffer += String(RFID.uid.uidByte[byte] &lt; 0x10 ? " 0" : " ") + String(RFID.uid.uidByte[byte], HEX);
  Serial.println("NUID: " + buffer);

  RFID.PICC_HaltA();
  RFID.PCD_StopCrypto1();
}
</code></pre>
 48706: <p>I had a similar problem. I used I2C to check if the board can see the reader. If I2C Bus doesn't detect your reader, then one of your soldering must be faulty... check with a meter and carefully re-solder the erring pin. </p>
 48909: <p>I have several of this board with this condition. As I checked ,they all return the same thing as you send in SPI . I think all of them have hardware problem. Common thing for all of them is In past I supplied them with switching supply and I think this is why they got broken(this chip is very sensitive with supply voltage and <strong>YOU MUST NOT CONNECT THEM TO MORE THAN 3.3V EVEN FOR VERY SHORT TIME</strong>) . I highly recommend use of Linear regulator for them   </p>
 67704: <p>Same problem as above. Three card readers. Two worked. One didn't. All three  readers had two pins bridged on the reader chip. The bridged pins were close to the pin 1 corner. I left the bridge alone as all three readers had the same bridge and one of the pins did not have a trace to it. The faulty card reader also had two pins bridged with solder in a different location. Both pins had separate traces. I removed the solder bridge and the faulty card reader was no longer faulty.</p>
 71475: <p>I figured out that one get these kind of problems (reader get´s firmware version but can not read tags) are related to power consumption. I tried to power the reader with Heltec Lora 32 Dev board and it schowed exactly this behaviour. Now, connected to another 3,3V source everything works as it should :)</p>
