user62332: I am creating a project that will read the RFID card or tag data, store that into a mysql database and display the data via PHP. 
I am using NodeMCU, RC522 RFID reader and Ardunio IDE to do that. 
Below is my Arduino code.  It successfully connects with WiFi (that I can see via serial monitor) but gives no response when I touch the RFID card to the reader.
I can't find the error.
/*
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # 
# RFID MFRC522 / RC522 Library : https://github.com/miguelbalboa/rfid # 
#                                                                     # 
#                 Installation :                                      # 
# NodeMCU ESP8266/ESP12E    RFID MFRC522 / RC522                      #
#         D2       <---------->   SDA/SS                              #
#         D5       <---------->   SCK                                 #
#         D7       <---------->   MOSI                                #
#         D6       <---------->   MISO                                #
#         GND      <---------->   GND                                 #
#         D1       <---------->   RST                                 #
#         3V/3V3   <---------->   3.3V                                #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #





#include <ESP8266WebServer.h>
#include <ESP8266HTTPClient.h>
#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN D2  //--> SDA / SS is connected to pinout D2
#define RST_PIN D1  //--> RST is connected to pinout D1
MFRC522 mfrc522(SS_PIN, RST_PIN);  //--> Create MFRC522 instance.

#define ON_Board_LED 2  //--> Defining an On Board LED, used for indicators when the process of connecting to a wifi router

//----------------------------------------SSID and Password of your WiFi router-------------------------------------------------------------------------------------------------------------//
const char* ssid = "apiece solution";
const char* password = "apiece@123";
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

ESP8266WebServer server(80);  //--> Server on port 80

int readsuccess;
byte readcard[4];
char str[32] = "";
String StrUID;

//-----------------------------------------------------------------------------------------------SETUP--------------------------------------------------------------------------------------//
void setup() {
  Serial.begin(115200); //--> Initialize serial communications with the PC
  SPI.begin();      //--> Init SPI bus
  mfrc522.PCD_Init(); //--> Init MFRC522 card

  delay(500);

  WiFi.begin(ssid, password); //--> Connect to your WiFi router
  Serial.println("hello");

  pinMode(ON_Board_LED,OUTPUT); 
  digitalWrite(ON_Board_LED, HIGH); //--> Turn off Led On Board

  //----------------------------------------Wait for connection
  Serial.print("Connecting");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    //----------------------------------------Make the On Board Flashing LED on the process of connecting to the wifi router.
    digitalWrite(ON_Board_LED, LOW);
    delay(250);
    digitalWrite(ON_Board_LED, HIGH);
    delay(250);
  }
  digitalWrite(ON_Board_LED, HIGH); //--> Turn off the On Board LED when it is connected to the wifi router.
  //----------------------------------------If successfully connected to the wifi router, the IP Address that will be visited is displayed in the serial monitor
  Serial.println("");
  Serial.print("Successfully connected to : ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  Serial.println("Please tag a card or keychain to see the UID !");
  Serial.println("");
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

//-----------------------------------------------------------------------------------------------LOOP---------------------------------------------------------------------------------------//
void loop() {
  // put your main code here, to run repeatedly
  readsuccess = getid();

  if(readsuccess) {  
  digitalWrite(ON_Board_LED, LOW);
    HTTPClient http;    //Declare object of class HTTPClient

    String UIDresultSend, postData;
    UIDresultSend = StrUID;

    //Post Data
    postData = "UIDresult=" + UIDresultSend;

   // http.begin("http://192.168.1.6/NodeMCU_RC522_Mysql/getUID.php");  //Specify request destination
    //http.addHeader("Content-Type", "application/x-www-form-urlencoded"); //Specify content-type header

    int httpCode = http.POST(postData);   //Send the request
    String payload = http.getString();    //Get the response payload

    Serial.println(UIDresultSend);
    Serial.println(httpCode);   //Print HTTP return code
    Serial.println(payload);    //Print request response payload

    http.end();  //Close connection
    delay(1000);
  digitalWrite(ON_Board_LED, HIGH);
  }
  else
  {
    Serial.println("hi");
     delay(1000); 
  }
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

//----------------------------------------Procedure for reading and obtaining a UID from a card or keychain---------------------------------------------------------------------------------//
int getid() {  
  if(!mfrc522.PICC_IsNewCardPresent()) {
    return 0;
  }
  if(!mfrc522.PICC_ReadCardSerial()) {
    return 0;
  }


  Serial.print("THE UID OF THE SCANNED CARD IS : ");

  for(int i=0;i<4;i++){
    readcard[i]=mfrc522.uid.uidByte[i]; //storing the UID of the tag in readcard
    array_to_string(readcard, 4, str);
    StrUID = str;
  }
  mfrc522.PICC_HaltA();
  return 1;
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

//----------------------------------------Procedure to change the result of reading an array UID into a string------------------------------------------------------------------------------//
void array_to_string(byte array[], unsigned int len, char buffer[]) {
    for (unsigned int i = 0; i < len; i++)
    {
        byte nib1 = (array[i] >> 4) & 0x0F;
        byte nib2 = (array[i] >> 0) & 0x0F;
        buffer[i*2+0] = nib1  < 0xA ? '0' + nib1  : 'A' + nib1  - 0xA;
        buffer[i*2+1] = nib2  < 0xA ? '0' + nib2  : 'A' + nib2  - 0xA;
    }
    buffer[len*2] = '\0';
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//


user63422: your code is OK, I've made a very similar project and... got the same issue. Solution was not in code only in power supply. RFID need very efficient current source and stable voltage. Check the power source, if you used 7805 as linear voltage stabilizer your project will don't work.

62332: <p>I am creating a project that will read the RFID card or tag data, store that into a mysql database and display the data via PHP. </p>

<p>I am using NodeMCU, RC522 RFID reader and Ardunio IDE to do that. </p>

<p>Below is my Arduino code.  It successfully connects with WiFi (that I can see via serial monitor) but gives no response when I touch the RFID card to the reader.</p>

<p>I can't find the error.</p>

<pre><code>/*
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # 
# RFID MFRC522 / RC522 Library : https://github.com/miguelbalboa/rfid # 
#                                                                     # 
#                 Installation :                                      # 
# NodeMCU ESP8266/ESP12E    RFID MFRC522 / RC522                      #
#         D2       &lt;----------&gt;   SDA/SS                              #
#         D5       &lt;----------&gt;   SCK                                 #
#         D7       &lt;----------&gt;   MOSI                                #
#         D6       &lt;----------&gt;   MISO                                #
#         GND      &lt;----------&gt;   GND                                 #
#         D1       &lt;----------&gt;   RST                                 #
#         3V/3V3   &lt;----------&gt;   3.3V                                #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #





#include &lt;ESP8266WebServer.h&gt;
#include &lt;ESP8266HTTPClient.h&gt;
#include &lt;SPI.h&gt;
#include &lt;MFRC522.h&gt;

#define SS_PIN D2  //--&gt; SDA / SS is connected to pinout D2
#define RST_PIN D1  //--&gt; RST is connected to pinout D1
MFRC522 mfrc522(SS_PIN, RST_PIN);  //--&gt; Create MFRC522 instance.

#define ON_Board_LED 2  //--&gt; Defining an On Board LED, used for indicators when the process of connecting to a wifi router

//----------------------------------------SSID and Password of your WiFi router-------------------------------------------------------------------------------------------------------------//
const char* ssid = "apiece solution";
const char* password = "apiece@123";
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

ESP8266WebServer server(80);  //--&gt; Server on port 80

int readsuccess;
byte readcard[4];
char str[32] = "";
String StrUID;

//-----------------------------------------------------------------------------------------------SETUP--------------------------------------------------------------------------------------//
void setup() {
  Serial.begin(115200); //--&gt; Initialize serial communications with the PC
  SPI.begin();      //--&gt; Init SPI bus
  mfrc522.PCD_Init(); //--&gt; Init MFRC522 card

  delay(500);

  WiFi.begin(ssid, password); //--&gt; Connect to your WiFi router
  Serial.println("hello");

  pinMode(ON_Board_LED,OUTPUT); 
  digitalWrite(ON_Board_LED, HIGH); //--&gt; Turn off Led On Board

  //----------------------------------------Wait for connection
  Serial.print("Connecting");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    //----------------------------------------Make the On Board Flashing LED on the process of connecting to the wifi router.
    digitalWrite(ON_Board_LED, LOW);
    delay(250);
    digitalWrite(ON_Board_LED, HIGH);
    delay(250);
  }
  digitalWrite(ON_Board_LED, HIGH); //--&gt; Turn off the On Board LED when it is connected to the wifi router.
  //----------------------------------------If successfully connected to the wifi router, the IP Address that will be visited is displayed in the serial monitor
  Serial.println("");
  Serial.print("Successfully connected to : ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  Serial.println("Please tag a card or keychain to see the UID !");
  Serial.println("");
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

//-----------------------------------------------------------------------------------------------LOOP---------------------------------------------------------------------------------------//
void loop() {
  // put your main code here, to run repeatedly
  readsuccess = getid();

  if(readsuccess) {  
  digitalWrite(ON_Board_LED, LOW);
    HTTPClient http;    //Declare object of class HTTPClient

    String UIDresultSend, postData;
    UIDresultSend = StrUID;

    //Post Data
    postData = "UIDresult=" + UIDresultSend;

   // http.begin("http://192.168.1.6/NodeMCU_RC522_Mysql/getUID.php");  //Specify request destination
    //http.addHeader("Content-Type", "application/x-www-form-urlencoded"); //Specify content-type header

    int httpCode = http.POST(postData);   //Send the request
    String payload = http.getString();    //Get the response payload

    Serial.println(UIDresultSend);
    Serial.println(httpCode);   //Print HTTP return code
    Serial.println(payload);    //Print request response payload

    http.end();  //Close connection
    delay(1000);
  digitalWrite(ON_Board_LED, HIGH);
  }
  else
  {
    Serial.println("hi");
     delay(1000); 
  }
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

//----------------------------------------Procedure for reading and obtaining a UID from a card or keychain---------------------------------------------------------------------------------//
int getid() {  
  if(!mfrc522.PICC_IsNewCardPresent()) {
    return 0;
  }
  if(!mfrc522.PICC_ReadCardSerial()) {
    return 0;
  }


  Serial.print("THE UID OF THE SCANNED CARD IS : ");

  for(int i=0;i&lt;4;i++){
    readcard[i]=mfrc522.uid.uidByte[i]; //storing the UID of the tag in readcard
    array_to_string(readcard, 4, str);
    StrUID = str;
  }
  mfrc522.PICC_HaltA();
  return 1;
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//

//----------------------------------------Procedure to change the result of reading an array UID into a string------------------------------------------------------------------------------//
void array_to_string(byte array[], unsigned int len, char buffer[]) {
    for (unsigned int i = 0; i &lt; len; i++)
    {
        byte nib1 = (array[i] &gt;&gt; 4) &amp; 0x0F;
        byte nib2 = (array[i] &gt;&gt; 0) &amp; 0x0F;
        buffer[i*2+0] = nib1  &lt; 0xA ? '0' + nib1  : 'A' + nib1  - 0xA;
        buffer[i*2+1] = nib2  &lt; 0xA ? '0' + nib2  : 'A' + nib2  - 0xA;
    }
    buffer[len*2] = '\0';
}
//------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------//
</code></pre>
 63422: <p>your code is OK, I've made a very similar project and... got the same issue. Solution was not in code only in power supply. RFID need very efficient current source and stable voltage. Check the power source, if you used 7805 as linear voltage stabilizer your project will don't work.</p>
