diff --git a/Readme.md b/Readme.md
index aa67d4f..c61234e 100644
--- a/Readme.md
+++ b/Readme.md
@@ -117,7 +117,4 @@ In order to perform a request, the library follows these steps:
 
 
 ## Development
-- Lint
-```
-cppcheck --enable=all .
-```
\ No newline at end of file
+- Lint: `cppcheck --enable=all .`
\ No newline at end of file
diff --git a/src/Ftp.cpp b/src/Ftp.cpp
index c346b89..ba4844b 100644
--- a/src/Ftp.cpp
+++ b/src/Ftp.cpp
@@ -44,8 +44,8 @@ const char CLOSE_GPRS_CONTEXT[] PROGMEM = "AT+SAPBR=0,1\r\n";
 const char REGISTRATION_STATUS[] PROGMEM = "AT+CREG?\r\n";
 const char SLEEP_MODE_2[] PROGMEM = "AT+CSCLK=2\r\n";
 
-const char OK[] PROGMEM = "OK";
-const char OK_[] = "OK";
+const char AT_OK[] PROGMEM = "OK";
+const char AT_OK_[] = "OK";
 const char AT_FTPPUT1_RESP[] PROGMEM = "1,1";
 const char AT_FTPPUT2_RESP[] PROGMEM = "+FTPPUT: 2";
 const char AT_FTPPUT20_RESP[] PROGMEM = "1,0";
@@ -68,30 +68,30 @@ Result FTP::putBegin(const char *apn,
   char tmp[24];
 
   delay(10000);
-  if (sendCmdAndWaitForResp_P(AT_FTPCID, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp_P(AT_FTPCID, AT_OK, 2000) == FALSE)
     return ERROR_FTPCID;
 
   strcpy_P(tmp, server);
   sprintf_P(buffer, AT_FTPSERV, tmp);
-  if (sendCmdAndWaitForResp(buffer, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp(buffer, AT_OK_, 2000) == FALSE)
     return ERROR_FTPSERV;
 
   strcpy_P(tmp, usr);
   sprintf_P(buffer, AT_FTPUN, tmp);
-  if (sendCmdAndWaitForResp(buffer, OK_, 2000) == FALSE)
+  if (sendCmdAndWaitForResp(buffer, AT_OK_, 2000) == FALSE)
     return ERROR_FTPUN;
 
   strcpy_P(tmp, pass);
   sprintf_P(buffer, AT_FTPPW, tmp);
-  if (sendCmdAndWaitForResp(buffer, OK_, 2000) == FALSE)
+  if (sendCmdAndWaitForResp(buffer, AT_OK_, 2000) == FALSE)
     return ERROR_FTPPW;
 
   sprintf_P(buffer, AT_FTPPUTNAME, fileName);
-  if (sendCmdAndWaitForResp(buffer, OK_, 2000) == FALSE)
+  if (sendCmdAndWaitForResp(buffer, AT_OK_, 2000) == FALSE)
     return ERROR_FTPPUTNAME;
 
   sprintf_P(buffer, AT_FTPPUTPATH, path);
-  if (sendCmdAndWaitForResp(buffer, OK_, 2000) == FALSE)
+  if (sendCmdAndWaitForResp(buffer, AT_OK_, 2000) == FALSE)
     return ERROR_FTPPUTPATH;
 
   if (sendCmdAndWaitForResp_P(AT_FTPPUT1, AT_FTPPUT1_RESP, 10000) == FALSE)
diff --git a/src/GPRS.cpp b/src/GPRS.cpp
index e396ab4..b5416f9 100644
--- a/src/GPRS.cpp
+++ b/src/GPRS.cpp
@@ -41,8 +41,8 @@ const char REGISTRATION_STATUS[] PROGMEM = "AT+CREG?\r\n";
 const char CONNECTED[] PROGMEM = "+CREG: 0,1";
 const char ROAMING[] PROGMEM = "+CREG: 0,5";
 const char BEARER_OPEN[] PROGMEM = "+SAPBR: 1,1";
-const char OK[] PROGMEM = "OK";
-const char OK_ = "OK";
+const char AT_OK[] PROGMEM = "OK";
+const char AT_OK_[] = "OK";
 
 Result openGPRSContext(SIM800 *sim800, const char *apn)
 {
@@ -56,8 +56,8 @@ Result openGPRSContext(SIM800 *sim800, const char *apn)
           sim800->sendCmdAndWaitForResp_P(REGISTRATION_STATUS, ROAMING, 2000) != TRUE) &&
          attempts < MAX_ATTEMPTS)
   {
-    sim800->sendCmdAndWaitForResp_P(READ_VOLTAGE, OK, 1000);
-    sim800->sendCmdAndWaitForResp_P(SIGNAL_QUALITY, OK, 1000);
+    sim800->sendCmdAndWaitForResp_P(READ_VOLTAGE, AT_OK, 1000);
+    sim800->sendCmdAndWaitForResp_P(SIGNAL_QUALITY, AT_OK, 1000);
     attempts++;
     delay(1000 * attempts);
     if (attempts == MAX_ATTEMPTS)
@@ -67,20 +67,20 @@ Result openGPRSContext(SIM800 *sim800, const char *apn)
     }
   }
 
-  if (sim800->sendCmdAndWaitForResp_P(BEARER_PROFILE_GPRS, OK, 2000) == FALSE)
+  if (sim800->sendCmdAndWaitForResp_P(BEARER_PROFILE_GPRS, AT_OK, 2000) == FALSE)
     result = ERROR_BEARER_PROFILE_GPRS;
 
   char httpApn[64];
   char tmp[24];
   strcpy_P(tmp, apn);
   sprintf_P(httpApn, BEARER_PROFILE_APN, tmp);
-  if (sim800->sendCmdAndWaitForResp(httpApn, OK_, 2000) == FALSE)
+  if (sim800->sendCmdAndWaitForResp(httpApn, AT_OK_, 2000) == FALSE)
     result = ERROR_BEARER_PROFILE_APN;
 
   while (sim800->sendCmdAndWaitForResp_P(QUERY_BEARER, BEARER_OPEN, 2000) == FALSE && attempts < MAX_ATTEMPTS)
   {
     attempts++;
-    if (sim800->sendCmdAndWaitForResp_P(OPEN_GPRS_CONTEXT, OK, 2000) == FALSE)
+    if (sim800->sendCmdAndWaitForResp_P(OPEN_GPRS_CONTEXT, AT_OK, 2000) == FALSE)
     {
       result = ERROR_OPEN_GPRS_CONTEXT;
     }
@@ -97,7 +97,7 @@ Result closeGPRSContext(SIM800 *sim800)
 {
   Result result = SUCCESS;
 
-  if (sim800->sendCmdAndWaitForResp_P(CLOSE_GPRS_CONTEXT, OK, 2000) == FALSE)
+  if (sim800->sendCmdAndWaitForResp_P(CLOSE_GPRS_CONTEXT, AT_OK, 2000) == FALSE)
     result = ERROR_CLOSE_GPRS_CONTEXT;
 
   return result;
diff --git a/src/Http.cpp b/src/Http.cpp
index b4dae6c..43fc25d 100644
--- a/src/Http.cpp
+++ b/src/Http.cpp
@@ -27,6 +27,7 @@
 
 #include "Http.h"
 #include "Parser.h"
+#include "GPRS.h"
 
 const char HTTP_INIT[] PROGMEM = "AT+HTTPINIT\r\n";
 const char HTTP_CID[] PROGMEM = "AT+HTTPPARA=\"CID\",1\r\n";
@@ -43,19 +44,18 @@ const char NORMAL_MODE[] PROGMEM = "AT+CFUN=1,1\r\n";
 const char SIGNAL_QUALITY[] PROGMEM = "AT+CSQ\r\n";
 const char READ_VOLTAGE[] PROGMEM = "AT+CBC\r\n";
 
-const char OK[] PROGMEM = "OK";
+const char AT_OK[] PROGMEM = "OK";
+const char AT_OK_[] = "OK";
 const char DOWNLOAD[] PROGMEM = "DOWNLOAD";
 const char HTTP_2XX[] PROGMEM = ",2XX,";
 const char HTTPS_PREFIX[] PROGMEM = "https://";
-const char OK_[] = "OK";
 
-#include "GPRS.h"
 
 Result HTTP::connect(const char *apn)
 {
   Result result = openGPRSContext(this, apn);
 
-  if (sendCmdAndWaitForResp_P(HTTP_INIT, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp_P(HTTP_INIT, AT_OK, 2000) == FALSE)
     result = ERROR_HTTP_INIT;
 
   return result;
@@ -65,7 +65,7 @@ Result HTTP::disconnect()
 {
   Result result = closeGPRSContext(this);
 
-  if (sendCmdAndWaitForResp_P(HTTP_CLOSE, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp_P(HTTP_CLOSE, AT_OK, 2000) == FALSE)
     result = ERROR_HTTP_CLOSE;
 
   return result;
@@ -132,7 +132,7 @@ unsigned int HTTP::readVoltage()
   cleanBuffer(voltage, sizeof(voltage));
 
   strcpy_P(buffer, READ_VOLTAGE);
-  sendCmd(buffer);
+  sendCmd(buffer, 500);
 
   if (readBuffer(buffer, sizeof(buffer)) == TRUE)
   {
@@ -179,20 +179,20 @@ Result HTTP::setHTTPSession(const char *uri)
   Result result = SUCCESS;
   char buffer[128];
 
-  if (sendCmdAndWaitForResp_P(HTTP_CID, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp_P(HTTP_CID, AT_OK, 2000) == FALSE)
     result = ERROR_HTTP_CID;
 
   sprintf_P(buffer, HTTP_PARA, uri);
-  if (sendCmdAndWaitForResp(buffer, OK_, 2000) == FALSE)
+  if (sendCmdAndWaitForResp(buffer, AT_OK_, 2000) == FALSE)
     result = ERROR_HTTP_PARA;
 
   bool https = strncmp_P(uri, HTTPS_PREFIX, strlen_P(HTTPS_PREFIX)) == 0;
-  if (sendCmdAndWaitForResp_P(https ? HTTPS_ENABLE : HTTPS_DISABLE, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp_P(https ? HTTPS_ENABLE : HTTPS_DISABLE, AT_OK, 2000) == FALSE)
   {
     result = https ? ERROR_HTTPS_ENABLE : ERROR_HTTPS_DISABLE;
   }
 
-  if (sendCmdAndWaitForResp_P(HTTP_CONTENT, OK, 2000) == FALSE)
+  if (sendCmdAndWaitForResp_P(HTTP_CONTENT, AT_OK, 2000) == FALSE)
     result = ERROR_HTTP_CONTENT;
 
   return result;
diff --git a/src/Sim800.cpp b/src/Sim800.cpp
index ec88888..ab2ac14 100644
--- a/src/Sim800.cpp
+++ b/src/Sim800.cpp
@@ -31,7 +31,7 @@
 const char SLEEP_MODE_2[] PROGMEM = "AT+CSCLK=2\r\n";
 const char SLEEP_MODE_1[] PROGMEM = "AT+CSCLK=1\r\n";
 const char SLEEP_MODE_0[] PROGMEM = "AT+CSCLK=0\r\n";
-const char OK[] PROGMEM = "OK";
+const char AT_OK[] PROGMEM = "OK";
 
 int SIM800::preInit(void)
 {
@@ -95,11 +95,11 @@ void SIM800::cleanBuffer(char *buffer, int count)
     }
 }
 
-void SIM800::sendCmd(const char *cmd)
+void SIM800::sendCmd(const char *cmd, unsigned int delayBeforeSend)
 {
     serialSIM800.listen();
     serialSIM800.flush();
-    delay(500);
+    delay(delayBeforeSend);
     write(cmd);
     serialSIM800.flush();
 }
@@ -203,11 +203,11 @@ void SIM800::sleep(bool force)
 {
     if (force)
     {
-        sendCmdAndWaitForResp_P(SLEEP_MODE_1, OK, 2000);
+        sendCmdAndWaitForResp_P(SLEEP_MODE_1, AT_OK, 2000);
     }
     else
     {
-        sendCmdAndWaitForResp_P(SLEEP_MODE_2, OK, 2000);
+        sendCmdAndWaitForResp_P(SLEEP_MODE_2, AT_OK, 2000);
     }
 }
 
diff --git a/src/Sim800.h b/src/Sim800.h
index 18a9f38..f699526 100644
--- a/src/Sim800.h
+++ b/src/Sim800.h
@@ -37,7 +37,7 @@
 #define DEFAULT_TIMEOUT 5000
 
 // Comment or uncomment this to debug the library
-#define DEBUG true
+// #define DEBUG true
 
 /** SIM800 class.
  *  Used for SIM800 communication. attention that SIM800 module communicate with MCU in serial protocol
@@ -87,8 +87,9 @@ class SIM800
 
     /** send AT command to SIM800 module
      *  @param cmd  command array which will be send to GPRS module
+     *  @param delayBeforeSend  integer indicating the sime to wait before sending a command
      */
-    void sendCmd(const char *cmd);
+    void sendCmd(const char *cmd, unsigned int delayBeforeSend = 10);
 
     /**send "AT" to SIM800 module
      */