Send low to all the 60 gpio pins on arduino when a button is pressed

jkprog

I am trying to send LOW to all the GPIO pins of the arduino mega 2560 using a QPushButton. I used the button clicked slot and using serial communication, I am am writing 0 to all the pins using serial port (turning off all the pins) . I am using a baud rate of 9600.
The problem is, when i click the button, only the first 9 pins turn off. The rest of the pins do not change there state from on to off. When I send high/low signal individually to each pin, it works fine for every pin, but it doesn't work when i try to do the same thing for all the pins simultaneously.

My code is:

void MainWindow::on_pushButton_clicked()
{
    serial.write("<on, 2, 1>");
    serial.write("<on, 3, 1>");
    serial.write("<on, 4, 1>");
    serial.write("<on, 5, 1>");
    serial.write("<on, 6, 1>");
    serial.write("<on, 7, 1>");
    serial.write("<on, 8, 1>");
    serial.write("<on, 9, 1>");
    serial.write("<on, 10, 1>");
    serial.write("<on, 11, 1>");
    serial.write("<on, 12, 1>");
    serial.write("<on, 13, 1>");
    serial.write("<on, 14, 1>");
    serial.write("<on, 15, 1>");
    serial.write("<on, 16, 1>");
    serial.write("<on, 17, 1>");
    serial.write("<on, 18, 1>");
    serial.write("<on, 19, 1>");
    serial.write("<on, 20, 1>");
    serial.write("<on, 21, 1>");
    serial.write("<on, 22, 1>");
    serial.write("<on, 23, 1>");
    serial.write("<on, 24, 1>");
    serial.write("<on, 25, 1>");
    serial.write("<on, 26, 1>");
    serial.write("<on, 27, 1>");
    serial.write("<on, 28, 1>");
    serial.write("<on, 29, 1>");
    serial.write("<on, 30, 1>");
    serial.write("<on, 31, 1>");

}

mrjj

Hi
Maybe its too much for the board in one go ?

jkprog

Can you suggest me a solution or an alternate way to do it? Because I need to have a button to turn on and off all the gpio pins of the arduino.

mrjj

@jkprog
You could try with a QTimer and only turn 1 off pr timer tick
so there will be a small delay between each command.

Like

class MainWindow : public QMainWindow {
  Q_OBJECT
 public:
  explicit MainWindow(QWidget* parent = 0);
  ~MainWindow();
  QTimer* timer; // <<<<<<<<<< the timer
  int ID = 2; // <<<<<<<<<< pin id 
 public slots:
  void MyTimerSlots(); // <<<<<< for timer to call
 private slots:
  void on_pushButton_clicked();
 private:
  Ui::MainWindow* ui;
};

and in .cpp

MainWindow::MainWindow(QWidget* parent) :
  QMainWindow(parent),
  ui(new Ui::MainWindow) {
  ui->setupUi(this);

  ID = 2; // member
  timer = new QTimer(this);
  connect(timer, SIGNAL(timeout()), this, SLOT(MyTimerSlots()) );

}

void MainWindow::MyTimerSlots() {
  QString OUT = QString  ("<on, %1, 1>").arg(ID++); // create the string
  qDebug() << OUT; // for testing
  //serial.write(OUT); // activate this again.
  if (ID > 32)  { timer->stop(); } // make sure it stops
}

void MainWindow::on_pushButton_clicked() {
  timer->start(500); // 500 ms. try less later
}

and you get pr 500 ms

"<on, 2, 1>"
"<on, 3, 1>"
"<on, 4, 1>"
"<on, 5, 1>"
"<on, 6, 1>"
"<on, 7, 1>"
"<on, 8, 1>"
"<on, 9, 1>"
"<on, 10, 1>"
"<on, 11, 1>"
"<on, 12, 1>"
"<on, 13, 1>"
"<on, 14, 1>"
"<on, 15, 1>"
...

So the exciting part if this works or its something else.

the test project.
https://www.dropbox.com/s/8j6lwdnrcahqd7i/serialtimer.zip?dl=0

jkprog

Running this program gives the following error:

error: no matching function for call to 'QSerialPort::write(QString&)'
serial.write(OUT);
^

mrjj

Note
Write wants char * or Qbytearray

you can do
serial.write(OUT.toStdString().c_str()); // ugly ;)

jkprog

The only change i made to the program was : serial.write(OUT.toStdString().c_str(),OUT.size() );
And its working.. :-)
Thank you :-)

mrjj

@jkprog
Super, so i guess the board needed a moment to process the input in between.
We are using 500 ms. You might be able to lower that to 100-200 for a faster on/off.

SGaist

Hi,

OUT.toLatin1() will be way cleaner.

mrjj

@SGaist

Thanks , i can never remember the name
as i want to to be called toByteArray ;)
Much cleaner than std::string + c_str()

jkprog

@SGaist thank you :)