HC-SR04 Ultrasonic Sensor Memory Problem

Hi everyone,

I got some code that is working fantastic. But i found it on the forums and i don't really understand it completely. After running once a second for about twenty minutes my N+2 runs out of  memory though. I think it gets to big a queue up of interrupts built up. That's what i guess from this thread.

I really need to poll this sensor at, at least 1 Hz but preferably 2 or 4. But it runs out of memory. Can someone suggest changes to the code to allow for this. Like I said earlier, It is otherwise perfect.

Here is the class.

using System;using System.Threading;using Microsoft.SPOT;using Microsoft.SPOT.Hardware;using SecretLabs.NETMF.Hardware;using SecretLabs.NETMF.Hardware.Netduino;namespace Pulsator{    public class Sonic    {        public static int uDistance;        private static int ticks;        private static InterruptPort EchoPin = new InterruptPort(Pins.GPIO_PIN_D2, true, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);        private static OutputPort TriggerPin = new OutputPort(Pins.GPIO_PIN_D1, false);        public static int Read()        {            EchoPin.OnInterrupt += new NativeEventHandler(port_OnInterrupt);            EchoPin.DisableInterrupt();                                      Distance();                //Debug.Print("distance = " + myDistance + " mm.");                Thread.Sleep(25);                return uDistance;        }        public static void Distance()        {            EchoPin.EnableInterrupt();            TriggerPin.Write(false);            Thread.Sleep(2);            TriggerPin.Write(true);            Thread.Sleep(10);            TriggerPin.Write(false);            Thread.Sleep(2);        }        private static void port_OnInterrupt(uint port, uint state, DateTime time)        {            if (state == 0) // falling edge, end of pulse            {                int pulseWidth = (int)time.Ticks - ticks;                // valid for 20°C                //int pulseWidthMilliSeconds = pulseWidth * 10 / 582;                //valid for 24°C                int pulseWidthMilliSeconds = (pulseWidth * 1 / (int)578.29); //change 1 to 10 for mm                //Debug.Print("Distance = " + pulseWidthMilliSeconds.ToString() + " millimètres.");                uDistance = pulseWidthMilliSeconds;            }            else            {                ticks = (int)time.Ticks;            }            EchoPin.ClearInterrupt();        }    }}

Here is how I call it.

            while (true)            {                lcd.Move(2, 0);                lcd.Show(Sonic.Read().ToString() + "cm ");                Thread.Sleep(1000);            }

Thanks in advance.

Hello Grant,

if you used the Read() method, you allocate each time a new Event, but it dont clear it. Try this to the Methode.

public static int Read(){   if(EchoPin.OnInterrupt == null)   {      EchoPin.OnInterrupt += new NativeEventHandler(port_OnInterrupt);   }   EchoPin.DisableInterrupt();                         Distance();   //Debug.Print("distance = " + myDistance + " mm.");   Thread.Sleep(25);   return uDistance;}

Heroduino

Thanks for the quick reply. I thought it was going to work but the first oninterrupt underlines and the error is

"the event 'microsoft.spot.hardware.nativeeventdispatcher.oninterupt can only appear on the left hand side of += or -="

if i change it to +=. it says that it can't convert void to bool?

Any other idea's. I'm way over my head?

Thanks Heaps. You live up to your name. I'm very grateful.

pls debug.print does not work. I don't know why because it doesn't give me any error and nothing happens too when i run the program