Displaying Text from Datalogger shield on OLED SSD1315 (arduino-seeds)?

Projects Programming
9

this is a hint that the OLED-object can't work with variable-type "String" directly.

But there is a variant to transform variable-type String into a so called c_str-ring.

try

String myTestStr = "ABC";
    Serial.println(myTestStr);
    Oled.println(myTestStr.c_str()  );

The variable type String is not well suited for RAM-limited microcontrollers.
There are some traps with Strings. Globally defined Strings eat up all memory over time and then the program will crash.
The alternatives are arrays of char (c-strings) or a library called SafeString wich you can install with the library-manager in the Arduino-IDE

Here is a demo-code how SafeStrings can be used

This demo-code has two debug-macros. Which reduce the the code you have to write to print to the serial monitor.
If you have questions about anything just ask

#define dbg(myFixedText, variableName) \
  Serial.print( F(#myFixedText " "  #variableName"=") ); \
  Serial.println(variableName);
// usage: dbg("1:my fixed text",myVariable);
// myVariable can be any variable or expression that is defined in scope

#define dbgi(myFixedText, variableName,timeInterval) \
  do { \
    static unsigned long intervalStartTime; \
    if ( millis() - intervalStartTime >= timeInterval ){ \
      intervalStartTime = millis(); \
      Serial.print( F(#myFixedText " "  #variableName"=") ); \
      Serial.println(variableName); \
    } \
  } while (false);
// usage: dbgi("2:my fixed text",myVar,myInterval);
// myVar can be any variable or expression that is defined in scope
// myInterval is the time-interval which must pass by before the next
// print is executed


#include <SafeString.h>
createSafeString(myDemo_SS, 32);
createSafeString(mySecondDemo_SS, 32);

unsigned long myCounter;

// if program starts printout the source-code filename etc. to the serial monitor
void PrintFileNameDateTime() {
  Serial.println( F("Code running comes from file ") );
  Serial.println(__FILE__);
  Serial.print( F("  compiled ") );
  Serial.print(__DATE__);
  Serial.print( F(" ") );
  Serial.println(__TIME__);  
}

//useful function for non-blocking timing
boolean TimePeriodIsOver (unsigned long &periodStartTime, unsigned long TimePeriod) {
  unsigned long currentMillis  = millis();  
  if ( currentMillis - periodStartTime >= TimePeriod )
  {
    periodStartTime = currentMillis; // set new expireTime
    return true;                // more time than TimePeriod) has elapsed since last time if-condition was true
  } 
  else return false;            // not expired
}

unsigned long MyTestTimer = 0;                   // variables MUST be of type unsigned long
const byte    OnBoard_LED = 13; // Arduino-Uno Onboard-LED is IO-pin 13

// make onboard-LED blink to show: "program is running"
void BlinkHeartBeatLED(int IO_Pin, int BlinkPeriod) {
  static unsigned long MyBlinkTimer;
  pinMode(IO_Pin, OUTPUT);
  
  if ( TimePeriodIsOver(MyBlinkTimer,BlinkPeriod) ) {
    digitalWrite(IO_Pin,!digitalRead(IO_Pin) ); 
  }
}



void setup() {
  Serial.begin(115200);
  Serial.println( F("Setup-Start") );
  PrintFileNameDateTime();
  myCounter = 0;
  myDemo_SS = "Hello world!";
}


void loop() {
  BlinkHeartBeatLED(OnBoard_LED,500);
  myCounter++;
  
  // loop is running very fast counting up very fast
  // but only once every 1234 milliseconds print 
  if ( TimePeriodIsOver(MyTestTimer,1234) ) {
    mySecondDemo_SS = myDemo_SS;  // assigning a SafeString to another SafeString
    
    mySecondDemo_SS += " ";       // append a SPACE
    mySecondDemo_SS += myCounter; // append integer-number
    Serial.println(mySecondDemo_SS);    
  }  

}

best regards Stefan