#include<SoftwareSerial.h> //If you are using an Uno, it only has 1 port

char dataIn;
unsigned long lgUpdateTime;
int sensorValue;

void setup()
{
         pinMode(A0, OUTPUT);
          Serial.begin(9600); //Receive data from App
         Serial1.begin(9600); //Write to Serial Monitor
         lgUpdateTime = millis();
}

void loop()
{
         //Excute loop every 1000 milliseconds, faster than the App sends to avoid buffer over-run
         
         if ((millis() - lgUpdateTime) > 1000)
         {
               lgUpdateTime = millis();
         
               if (Serial.available() > 0)
               {
                         dataIn = Serial.read();
                         Serial1.println(dataIn);
               }
         
               switch (dataIn)
               {
                         case 'T':
                                   sensorValue = analogRead(A0);
                                   Serial1.println('T');
                                   Serial1.println(sensorValue);
                                   break;
                         
                         case 'W':
                                   Serial1.println('W');
                                   break;
               }
         }
}