diff --git a/src/Module.cpp b/src/Module.cpp
index 4ff5cf79..00560460 100644
--- a/src/Module.cpp
+++ b/src/Module.cpp
@@ -49,10 +49,6 @@ void Module::ATemptyBuffer() {
   }
 }
 
-bool Module::ATsendCommand(String& cmd) {
-  return(ATsendCommand(cmd.c_str()));
-}
-
 bool Module::ATsendCommand(const char* cmd) {
   ATemptyBuffer();
   ModuleSerial->print(cmd);
diff --git a/src/Module.h b/src/Module.h
index 8f773734..fbbb6649 100644
--- a/src/Module.h
+++ b/src/Module.h
@@ -23,7 +23,6 @@ class Module {
     
     void ATemptyBuffer();
     bool ATgetResponse();
-    bool ATsendCommand(String& cmd);
     bool ATsendCommand(const char* cmd);
     bool ATsendData(uint8_t* data, uint32_t len);
     
diff --git a/src/modules/ESP8266.cpp b/src/modules/ESP8266.cpp
index f45012ff..2f802cd3 100644
--- a/src/modules/ESP8266.cpp
+++ b/src/modules/ESP8266.cpp
@@ -67,12 +67,12 @@ uint8_t ESP8266::join(const char* ssid, const char* password) {
   strcat(cmd, "\",\"");
   strcat(cmd, password);
   strcat(cmd, "\"");
-
-  if(!_mod->ATsendCommand(cmd)) {
-    delete[] cmd;
+  
+  bool res = _mod->ATsendCommand(cmd);
+  delete[] cmd;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
-  delete[] cmd;
   
   // disable multiple connection mode
   if(!_mod->ATsendCommand("AT+CIPMUX=0")) {
@@ -392,13 +392,12 @@ uint8_t ESP8266::send(const char* data) {
   strcat(cmd, lenStr);
   
   // send data length in bytes
-  if(!_mod->ATsendCommand(cmd)) {
-    delete[] cmd;
+  bool res = _mod->ATsendCommand(cmd);
+  delete[] cmd;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
   
-  delete[] cmd;
-  
   // send data
   if(!_mod->ATsendCommand(data)) {
     return(ERR_AT_FAILED);
@@ -417,13 +416,12 @@ uint8_t ESP8266::send(uint8_t* data, uint32_t len) {
   strcat(cmd, lenStr);
   
   // send command and data length in bytes
-  if(!_mod->ATsendCommand(cmd)) {
-    delete[] cmd;
+  bool res = _mod->ATsendCommand(cmd);
+  delete[] cmd;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
   
-  delete[] cmd;
-  
   // send data
   if(!_mod->ATsendData(data, len)) {
     return(ERR_AT_FAILED);
@@ -472,12 +470,12 @@ uint8_t ESP8266::openTransportConnection(const char* host, const char* protocol,
     strcat(cmd, tcpKeepAliveStr);
   }
   
-  if(!_mod->ATsendCommand(cmd)) {
-    delete[] cmd;
+  bool res = _mod->ATsendCommand(cmd);
+  delete[] cmd;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
   
-  delete[] cmd;
   return(ERR_NONE);
 }
 
diff --git a/src/modules/XBee.cpp b/src/modules/XBee.cpp
index 39497193..46096ab6 100644
--- a/src/modules/XBee.cpp
+++ b/src/modules/XBee.cpp
@@ -49,7 +49,7 @@ uint8_t XBee::begin(long speed) {
   return(ERR_NONE);
 }
 
-uint8_t XBee::setDestinationAddress(const char destinationAddressHigh[], const char destinationAddressLow[]) {
+uint8_t XBee::setDestinationAddress(const char* destinationAddressHigh, const char* destinationAddressLow) {
   // enter command mode
   DEBUG_PRINTLN_STR("Entering command mode ...");
   if(!enterCmdMode()) {
@@ -58,17 +58,23 @@ uint8_t XBee::setDestinationAddress(const char destinationAddressHigh[], const c
   
   // set higher address bytes
   DEBUG_PRINTLN_STR("Setting address (high) ...");
-  String addressHigh = "ATDH";
-  addressHigh += destinationAddressHigh;
-  if(!_mod->ATsendCommand(addressHigh)) {
+  char* addressHigh = new char[strlen(destinationAddressHigh) + 4];
+  strcpy(addressHigh, "ATDH");
+  strcat(addressHigh, destinationAddressHigh);
+  bool res = _mod->ATsendCommand(addressHigh);
+  delete[] addressHigh;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
   
   // set lower address bytes
   DEBUG_PRINTLN_STR("Setting address (low) ...");
-  String addressLow = "ATDL";
-  addressLow += destinationAddressLow;
-  if(!_mod->ATsendCommand(addressLow)) {
+  char* addressLow = new char[strlen(destinationAddressLow) + 4];
+  strcpy(addressLow, "ATDL");
+  strcat(addressLow, destinationAddressLow);
+  res = _mod->ATsendCommand(addressLow);
+  delete[] addressLow;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
   
@@ -81,7 +87,7 @@ uint8_t XBee::setDestinationAddress(const char destinationAddressHigh[], const c
   return(ERR_NONE);
 }
 
-uint8_t XBee::setPanId(const char panId[]) {
+uint8_t XBee::setPanId(const char* panId) {
   // enter command mode
   DEBUG_PRINTLN_STR("Entering command mode ...");
   if(!enterCmdMode()) {
@@ -90,9 +96,12 @@ uint8_t XBee::setPanId(const char panId[]) {
   
   // set PAN ID
   DEBUG_PRINTLN_STR("Setting PAN ID ...");
-  String panIdCmd = "ATID";
-  panIdCmd += panId;
-  if(!_mod->ATsendCommand(panIdCmd)) {
+  char* cmd = new char[strlen(panId) + 4];
+  strcpy(cmd, "ATID");
+  strcat(cmd, panId);
+  bool res = _mod->ATsendCommand(cmd);
+  delete[] cmd;
+  if(!res) {
     return(ERR_AT_FAILED);
   }
   
diff --git a/src/modules/XBee.h b/src/modules/XBee.h
index 9222bca5..8b63e0c4 100644
--- a/src/modules/XBee.h
+++ b/src/modules/XBee.h
@@ -54,8 +54,8 @@ class XBee: public ISerial {
     
     uint8_t begin(long speed);
     
-    uint8_t setDestinationAddress(const char destinationAddressHigh[], const char destinationAddressLow[]);
-    uint8_t setPanId(const char panId[]);
+    uint8_t setDestinationAddress(const char* destinationAddressHigh, const char* destinationAddressLow);
+    uint8_t setPanId(const char* panId);
     
   private:
     bool enterCmdMode();