DTHrecv.c

String sCommand = "";
char cTemp;
int receiveFlag = 0;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(receiveFlag) {
    Serial.println(sCommand);
    receiveFlag = 0; 
    sCommand = "";
  }
}

void serialEvent(void) 
{
  while(Serial.available())
  {
     cTemp = Serial.read();
     if(cTemp == '\n') {  // 개행까지 받는다
        receiveFlag = 1;
        return;
     }
     sCommand += cTemp;
  }
}

DTHsend.c

#include <DHT.h>
#define DHTTYPE DHT11

int pinDht = 2;
char buf1[30], buf2[30];

DHT dht(pinDht, DHTTYPE);

void setup() {
  Serial.begin(115200); 

  dht.begin();
}

void loop() {
  delay(1000);
  float fTemp = dht.readTemperature();
  float fHumi = dht.readHumidity();
  
  if (isnan(fTemp) || isnan(fHumi)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  String msg1 = "Temperature: ";
  msg1 += fTemp;
  msg1 += "[C]\t\n";

  String msg2 = "Humidity: ";
  msg2 += fHumi;
  msg2 += "[%]\n";

  String msg1 = "TH";
  
  msg1.toCharArray(buf1, 30);
  msg2.toCharArray(buf2, 30);
   
  Serial.write(buf1);
  Serial.write(buf2);
}