How can I count pulse inputs with some interval time? - raspberry-pi

Question

I'm develop a pulse counter(coin counter) in raspberry pi with windows 10 iot core, and i need to count pulses that have a interval time of 25 miliseconds like this:
0,05€ - 1 pulse
0,10€ - 2 pulses
0,20€ - 4 pulses
0,50€ - 10 pulses
1€ - 20 pulses
2€ - 40 pulses
like this image: pulses
I need to print the number of pulses(to have the value inserted) when the interval time is diferent of 25 miliseconds.
I have this code:
public MainPage()
{
this.InitializeComponent();
InitGPIO();
}
private void InitGPIO()
{
var gpio = GpioController.GetDefault();
if (gpio == null)
{
GpioStatus.Text = "There is no GPIO controller on this device.";
}
coinPin = gpio.OpenPin(coin_Pin);
if (coinPin.IsDriveModeSupported(GpioPinDriveMode.InputPullUp))
{
coinPin.SetDriveMode(GpioPinDriveMode.InputPullUp);
} else
{
coinPin.SetDriveMode(GpioPinDriveMode.Input);
}
coinPin.DebounceTimeout = TimeSpan.FromMilliseconds(25);
coinPin.ValueChanged += coinPin_ValueChanged;
GpioStatus.Text = "GPIO pins initialized correctly.";
}
private void coinPin_ValueChanged(GpioPin sender, GpioPinValueChangedEventArgs e)
{
if (e.Edge == GpioPinEdge.FallingEdge)
{
counter++;
}
var task = Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
if (e.Edge == GpioPinEdge.FallingEdge)
{
//counter++;
var time = PulseIn(coinPin, e.Edge);
value = (counter * 5);
value100 = value / 100;
//money.Text = "Eur: " + (decimal)value100 + " €";
if (time != 25)
{
money.Text = "Eur: " + (decimal)value100 + " €";
GpioStatus.Text = "" + time;
} else
{
GpioStatus.IsEnabled = false;
}
//GpioStatus.Text = "" + time + "";
} else
{
///GpioStatus.Text = "" + coinPin.DebounceTimeout;
}
});
}
private double PulseIn(GpioPin pin, GpioPinEdge edge)
{
var sw = new Stopwatch();
while (edge.Equals(GpioPinEdge.RisingEdge))
{
//sw.Start();
}
sw.Start();
if (!edge.Equals(GpioPinEdge.RisingEdge))
{
//sw.Stop();
}
sw.Stop();
return sw.Elapsed.TotalMilliseconds;
}
private const int coin_Pin = 24;
private int counter = 0;
private double value = 0;
private double value100 = 0;
private GpioPin coinPin;
Can you help me please?
Thank you very much.

Answer 1

From your code,
sw.Start();
if (!edge.Equals(GpioPinEdge.RisingEdge))
{
//sw.Stop();
}
sw.Stop();
it actually measures the execute time of the if statement that between sw.Start() and sw.Stop(). This does not make sense. Record the watch.Elapsed.TotalMilliseconds when the falling edge arrived and restart the stopwatch to measure the pulse interval time. To do this, I add the following two code lines under counter++, remove var time = PulseIn(coinPin, e.Edge) and use timeinterval in GpioStatus.Text = "" + timeinterval instead.
timeinterval = watch.Elapsed.TotalMilliseconds;
watch.Restart();
The following is complete code piece:
private Stopwatch watch = new Stopwatch();
private void coinPin_ValueChanged(GpioPin sender, GpioPinValueChangedEventArgs e)
{
double timeinterval = 0;
if (e.Edge == GpioPinEdge.FallingEdge)
{
counter++;
timeinterval = watch.Elapsed.TotalMilliseconds;
watch.Restart();
}
var task = Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
if (e.Edge == GpioPinEdge.FallingEdge)
{
//var time = PulseIn(coinPin, e.Edge);
value = (counter * 5);
value100 = value / 100;
if (timeinterval != 25)
{
money.Text = "Eur: " + (decimal)value100 + " €";
GpioStatus.Text = "" + timeinterval;
}
//...
}
});
}
You can try above code piece to see if it meets your accuracy requirement.
Note: It is not suitable to measure hardware pulse interval in software level because the software jitter is always unpredictable.