Ethernet Shield Stops After a While - arduino

Question

I use Ethernet shield (W5100) and RC522 on my Arduino Uno. It works 1 or 2 hours (sometimes 15 minutes - sometimes 2 days) After this random time, it stops working. I mean stop with, RC-522 module don't read cards, and ethernet shield can't connect server. When i unplug power (1.5A - 12 V power suply) and re-plug it, it starts working successfully.
I need to this system works forever... This system reads mifare card, and sends to the server, after that it checks reply, and if the reply is "1", it triggers relay. (relay is 5V simple relay)
Some people said "Change your adaptor", and i changed it, nothing changed.
Some people said " use 10 microfarad capasitor between rst and gnd pin" and nothing changed.
and some people said, "this is arduino dude, it is for just studend give up and use stm32", and i didn't apply this suggestion yet. I want to know why this happens.
#include <SPI.h>
#include <Ethernet.h>
#include <MFRC522.h>
//Mac address of ethernet shield
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEA };
//My Network info, i use static ip
byte ip[] = { 172, 16, 64, 78 };
byte gateway[] = { 172, 16, 64, 1 };
byte myserver[] = { 172, 16, 64, 46 };
byte subnet[] = { 255, 255, 255, 0 };
String CardInfo = "";
EthernetClient client;
String GateNo = "0";
String DeviceNo = "100";
String Answer = "";
MFRC522 mfrc522;
byte Key[] = { 0xff,0xff,0xff,0xff,0xff,0xff };
MFRC522::MIFARE_Key key;
void setup(){
//Disabling SD Card
pinMode(4,OUTPUT);
digitalWrite(4,HIGH);
Ethernet.begin(mac, ip, subnet, gateway);
KeyCreate();
mfrc522.PCD_Init(2, 8);
mfrc522.PCD_DumpVersionToSerial();
}
void sendGET()
{
//I used this line to guarantee the disconnect from server
client.stop();
Answer = "";
if (client.connect(myserver, 81)) {
client.println("GET /AccessCheck/CardNo=" + CardInfo + "&GateNo=" + GateNo + "&DeviceNo=" + DeviceNo + " HTTP/1.0");
client.println("Authorization: Basic xxxxxxxxxxxx");
client.println();
}
else {
//Ethernet.begin(mac, ip, subnet, gateway);
return;
}
int connectLoop = 0;
while(client.connected())
{
while(client.available())
{
char c = client.read();
Answer = Answer + c;
connectLoop = 0;
}
delay(1);
connectLoop++;
if(connectLoop > 5000)
{
client.stop();
return;
}
}
client.stop();
}
//This function disables eth and enable rc522 (and reverse)
void Switch(int i)
{
switch (i)
{
case 0:
digitalWrite(10, HIGH);
digitalWrite(2, LOW);
break;
case 1:
digitalWrite(2, HIGH);
digitalWrite(10, LOW);
break;
}
}
void AccessControl()
{
int AnswerLength = Answer.length();
pinMode(5, OUTPUT);
digitalWrite(5, HIGH);
if(Answer[AnswerLength-1] == 49)
{
digitalWrite(5, LOW);
delay(100);
digitalWrite(5, HIGH);
}
pinMode(5, INPUT);
pinMode(6, INPUT);
delay(1000);
}
void ReadCard()
{
byte len = 18;
MFRC522::StatusCode status;
byte MyBuffer[18];
status = mfrc522.PCD_Authenticate(MFRC522::PICC_CMD_MF_AUTH_KEY_A, 10, &key, &(mfrc522.uid));
status = mfrc522.MIFARE_Read(10, MyBuffer, &len);
int counter = 0;
//This line is check for turkish character
if(MyBuffer[0] == 221)
{
CardInfo = "X";
for (int i = 1; i < 16; i++)
{
if (MyBuffer[i] != 32)
{
CardInfo = CardInfo + (char)MyBuffer[i];
}
}
}
else
{
CardInfo = "";
for (int i = 0; i < 16; i++)
{
if (MyBuffer[i] != 32)
{
CardInfo = CardInfo + (char)MyBuffer[i];
}
}
}
mfrc522.PICC_HaltA();
mfrc522.PCD_StopCrypto1();
return;
}
void KeyCreate()
{
for (int i = 0; i < 6; i++)
{
key.keyByte[i] = Key[i];
}
}
void loop(){
Switch(0);
if (mfrc522.PICC_IsNewCardPresent() && mfrc522.PICC_ReadCardSerial()) {
ReadCard();
Switch(1);
sendGET();
AccessControl();
}
}
I expect it runs without freezing
Actual result is ethernet shield freezes after a while

Answer 1

I am using watchdog in some script . This functionality could reset auomatically your arduino if you dont reset the watchdog during the lapse.
you execute wdt_enable() in the setup() and wd_reset() at the beginning of the loop
time before watchdog firing argument of wdt_enable()
-------------------------------------------------------
15mS WDTO_15MS
30mS WDTO_30MS
60mS WDTO_60MS
120mS WDTO_120MS
250mS WDTO_250MS
500mS WDTO_500MS
1S WDTO_1S
2S WDTO_2S
4S WDTO_4S
8S WDTO_8S
example of use:
#include <avr/wdt.h>
void setup()
{
wdt_enable(WDTO_4S); // enable the watchdog
// will fire after 4s without reset
}
void loop(){
wdt_reset(); // resets the watchdog timer count
:
:
// if program hangs more than 4s, launch the reset of arduino
}