Serial Communication Arduino C++ Builder

Question

I am trying to write an Application with C++ Builder which should display for example the temperature and humidity of a measurement from the Arduino. Arduino and my Application are connected via TComPort. I am using a Baudrate of 115200.

VCL Code:

AnsiString temp, hum;

ComPort1->ReadStr(temp, 5);
RichEdit1->Text = temp;

ComPort1->ReadStr(hum, 5);
RichEdit3->Text = hum;

Arduino Code:

DHT dht(10, DHT11);

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

void loop(void)
{
// Measure the humidity & temperature
float h = dht.readHumidity();
float t = dht.readTemperature();

// Transform to String
String temp = String( t );
String hum =  String( h );
delay(10);
Serial.print(temp);
Serial.print(hum); 

delay(5000);

}

When I start my Application (VCL with C++ Builder) and connect to the Arduino every 5 seconds, the values should be refreshed by new values. Most of the time the 2 values are correct and it displays like it should for example Temperature: 24:00 Humidity: 55.00 But for some reason every now and then it displays something like this: Temperature: .0051 Humditiy: .00

or some other weird values. 5 seconds later the values are correct again. This happens every 20-30 seconds 1 time and i dont know why this keeps happening.

Looks like you are occasionally catching it in the middle of a transmission. When you see the weird ones, are the ones right before or after them right? OR do the messed up ones seem to come in pairs? — Delta_G
And why are you converting the temp and humidity values to String before you print them? You know the Print class can handle floats all by itself. The String class is a memory waster and a memory fragmenter that shouldn't be used on any serious microcontroller project. — Delta_G
Hey many thanks for yout comment, first thanks i didnz know that with the strings class :) i will change that, second normally the first ones are right values then both values in pair get so weird and the next ones are alright again so like in between they are weird. There are little few times were there were 2 weird ones in a row. — kevin
Well there doesn't seem to be any issue in the sending code. The problem almost has to be on the receiving side. — Delta_G
I noticed that when i set the baudrate to 9600 i am not getting any good values, after setting it to 115200 there are only few weird ones left but thats all i figured out so far — kevin

Remy Lebeau Remy Lebeau · Accepted Answer · 2017-11-07T03:46:27

In the TComPort.OnRxChar event, there is a Count parameter that tells you how many bytes are available. Don't read more than that. Buffer the bytes to the side, and then read only complete values from that buffer.

For example:

private:
    AnsiString ComPortBuffer;

void __fastcall TMyForm::ComPort1RXChar(TObject *Sender, int Count)
{
    AnsiString s;

    int len = ComPort1->ReadStr(s, 5);
    if (len > 0)
    {
        if (len < 5)
            s.SetLength(len);
        ComPortBuffer += s;
    }

    while (ComPortBuffer.Length() >= 10)
    {
        AnsiString temp = ComPortBuffer.SubString(1, 5);
        AnsiString hum  = ComPortBuffer.SubString(6, 5);
        ComPortBuffer.Delete(1, 10);

        // use temp and hum as needed...
        RichEdit1->Text = temp;
        RichEdit3->Text = hum;
    }
}

Serial Communication Arduino C++ Builder

1 Answers