Qt UI to Arduino Serial connection. Setup called multiple times - c++

Question

I have noticed that setup() is executed again and again. I receive the same messages from setup()
Here's the code:
enum flags{
RFID= 1,
LASER_ON= 2,
LASER_OFF= 4,
.
.
.
};
int inByte;
bool fcount = false;
unsigned int count=0;
long average_input=0;
bool cont = false;
int prev=-1;
/**
* Initialize.
*/
void setup() {
Serial.begin(9600); // Initialize serial communications with the PC
// while (!Serial);// Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
// Serial1.begin(19200);
// while (!Serial1);
// SPI.begin(); // Init SPI bus
// mfrc522.PCD_Init(); // Init MFRC522 card
pinMode(laser, OUTPUT);
pinMode(13, OUTPUT);
// Prepare the key (used both as key A and as key B)
// using FFFFFFFFFFFFh which is the default at chip delivery from the factory
// for (byte i = 0; i < 6; i++) {
// key.keyByte[i] = 0xFF;
// }
Serial.println(F("Scan a MIFARE Classic PICC to demonstrate read and write."));
Serial.print(F("Using key (for A and B):"));
// dump_byte_array(key.keyByte, MFRC522::MF_KEY_SIZE);
Serial.println();
Serial.println(F("BEWARE: Data will be written to the PICC, in sector #1"));
digitalWrite(laser, HIGH);
for(byte i =0; i<10 ; i++){
average_input += analogRead(photocell);
delay(10);
}
Serial.print("total sum=\t");Serial.println(average_input);
average_input /=10;
Serial.print("average=\t");Serial.println(average_input);
digitalWrite(laser, LOW);
}
/**
* Main loop.
*/
void loop() {
if(Serial.available()){
delay(2000);
Serial.println("Serial available");
int input = 0;
while (Serial.available()){
input = input*10 + (Serial.read()-48);
inByte = input;
}
Serial.println(inByte);
}
// if(Serial1.available()){
// delay(100);
// Serial.println("Serial1 available");
// int input = 0;
// while (Serial1.available()){
// input = input*10 + (Serial1.read()-48);
// inByte = input;
// }
// Serial.println(inByte);
// }
switch(inByte){
case RFID:
Serial.println("RFID CHOSEN");
// get_rfid();
break;
case LASER_ON:
digitalWrite(laser, HIGH);
fcount=true;
break;
case LASER_OFF:
digitalWrite(laser, LOW);
fcount=false;
break;
.
.
.
}
if (fcount){
.
.
.
}
As you can see I commented out a lot, just trying to make setup() run only once. As the general goal: I'm trying to connect my Qt UI through QSerialPort. I've found a good solution on similar topic and adopted it. Here's the Qt code:
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.
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QSerialPort serial;
QStringList ports;
for (QSerialPortInfo port : QSerialPortInfo::availablePorts()){
qDebug() << port.portName() << port.vendorIdentifier() << port.productIdentifier()
<< port.hasProductIdentifier() << port.hasVendorIdentifier() << port.isBusy();
ports += port.portName();
}
serial.setPortName("cu.usbmodem1471");
serial.open(QIODevice::ReadWrite);
serial.setBaudRate(QSerialPort::Baud9600);
serial.setDataBits(QSerialPort::Data8);
serial.setParity(QSerialPort::NoParity);
serial.setStopBits(QSerialPort::OneStop);
serial.setFlowControl(QSerialPort::NoFlowControl);
qDebug()<<serial.isOpen()<<endl;
qDebug()<<serial.isWritable()<<endl;
if (serial.isOpen() && serial.isWritable())
{
QByteArray ba("2");
serial.write(ba);
//serial.flush();
qDebug() << "data has been send" << endl;
serial.close();
}
.
.
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First of all, it shows false false on both isOpen() and isWritable() when the serial monitor is opened. My guess is that Qt is trying to connect/send data to the same Serial as PC getting data on. When the Serial monitor is closed the flags are set to true true and message is sent. However it goes through the same setup process (aka calibrating laser) and not receiving 2 as a flag to turn on laser. Please advice me on Serial communication between PC and Arduino.

Answer 1

The serial port is used exclusively by an application, either SerialMonitor or Qt.
Opening a COM port (both by SerialMonitor or Qt) usually triggers a reset of the Arduino. That's why setup() is running.
This is used to make uploading of new sketches easier.
It's achieved by toggling the Serial control signal DTR.
I'm not a Qt expert to know exactly how to disable this on the PC side. Some terminal programs give you control over that DTR signal.
Possible workarounds:
Open the Serial line only once and keep it open as long as your Qt app is active.
If you have a 10 µF capacitor or similar, plug it into the Arduino between GND and RESET. This should inhibit the automatic reset. (Remove it to upload new sketch)