解决Arduino通过PHP脚本向数据库发送数据时遇到的问题

#include <SPI.h>
#include <Ethernet.h>
#define POWER_PIN_WATER_SENS 7
#define SIGNAL_PIN_WATER_SENS A5
#define SOUND_PIN A0
byte mac[] = {0x00, 0xAA, 0xBB, 0xCC, 0xDE, 0x02};
int waterLevel = 0;
String waterLevelString;     
EthernetClient client;
void setup() {

  Serial.begin(9600);
  pinMode(POWER_PIN_WATER_SENS,OUTPUT);
  digitalWrite(POWER_PIN_WATER_SENS, LOW);  
  Serial.println("Initialize Ethernet with DHCP:");
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
      Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
    } else if (Ethernet.linkStatus() == LinkOFF) {
      Serial.println("Ethernet cable is not connected.");
    }
    while (true) {
      delay(1);
    }
  }
  Serial.print("My IP address: ");
  Serial.println(Ethernet.localIP());
}

void loop() {
  switch (Ethernet.maintain()) {
    case 1:
      //renewed fail
      Serial.println("Error: renewed fail");
      break;

    case 2:
      //renewed success
      Serial.println("Renewed success");
      //print your local IP address:
      Serial.print("My IP address: ");
      Serial.println(Ethernet.localIP());
      break;

    case 3:
      //rebind fail
      Serial.println("Error: rebind fail");
      break;

    case 4:
      //rebind success
      Serial.println("Rebind success");
      //print your local IP address:
      Serial.print("My IP address: ");
      Serial.println(Ethernet.localIP());
      break;

    default:
      //nothing happened
      break;
  }
  digitalWrite(POWER_PIN_WATER_SENS, HIGH);
  delay(100);
  waterLevel = analogRead(SIGNAL_PIN_WATER_SENS);
  digitalWrite(POWER_PIN_WATER_SENS, LOW);
  Serial.print("Water: ");
  //waterLevel = 1; //debug value
  Serial.println(waterLevel);
  waterLevelString = "waterlevel=" + (String)waterLevel;


    if (client.connect("<snip>", 80)) {
    client.print("GET /arduino_connect_to_db.php?");
    client.print(waterLevelString);
    client.println(" HTTP/1.1");
    client.println("Host: <snip>");
    client.println("User-Agent: arduino");
    client.println("Accept: */*");
    client.println();
  }
    if (client.connected()) { 
    client.stop();
  }
    delay(3000);
  }