checking for double threshold - c++

Question

I've a basic question to implement an algorithm to detect a threshold for a realtime signal.
For ex. If I've a signal as shown below, I need to check if the signal crossing two thresholds in a fixed period of time, say 3 seconds.
My question here is, What will be set of IF statements to check for two thresholds in a fixed time period?
What I've already got:
I can check for a single threshold, as below:
if(signal > onThreshold)
{
ui->rdo_btn_vertical->setStyleSheet(StyleSheetOn1); // change appearance of a radio button
QSound::play(":/res/beep1.wav"); // make a beep sound as well
}
else
{
ui->rdo_btn_vertical->setStyleSheet(StyleSheetOff1);
}

Answer 1

First, we create a helper that detects upwards crossings:
class DetectUpwardsCrossing : public QObject {
public:
DetectUpwardsCrossing(double threshold, QObject *parent = nullptr) : QObject(parent), threshold(threshold), current(qSNaN()) {}
signals:
void crossing();
public slots:
void onSignal(double value) {
if (qIsNaN(current)) {
current = value;
return;
}
if (current == value) {
return;
}
bool before = current <= threshold;
current = value;
bool after = current >= threshold;
if (before && after) {
emit crossing();
}
}
private:
double threshold, current;
};
Now create an instance of DetectUpwardsCrossing, hook up your incoming signal value to onSignal and hook its crossing signal to the following method:
void onCrossing() {
QSound::play(":/res/beep1.wav"); // make a beep sound
if (crossingTimer->isActive()) { // The timer is still running, so we are within the 3s period
ui->rdo_btn_vertical->setStyleSheet(StyleSheetOn1); // change appearance of a radio button
}
crossingTimer->restart();
}
void crossingTimerExpire() {
ui->rdo_btn_vertical->setStyleSheet(StyleSheetOff1);
crossingTimer->stop();
}
The final piece is a QTimer *crossingTimer with an interval of 3 seconds, whose timeout signal is hooked up to crossingTimerExpire.
By using a timer like this, you can ensure that the display turns "off" if you suddenly no longer receive signals.