Netduino 3 Wifi pollution Sensor Part 2

In a previous post I had started building a driver for the Seeedstudio Grove Dust Sensor. It was a proof of concept and it didn’t handle some edge cases well.

While building the pollution monitor with a student we started by simulating the negative occupancy of the Shinyei PPD42NJ Particle sensor with the Netduino’s on-board button. This worked and reduced initial complexity. But it also made it harder to simulate the button being pressed as the program launches (the on-board button is also the reset button), or simulate if the button was pressed at the start or end of the period.

Dust sensor simulation with button

Netduino 3 Wifi Test Harness

The first sample code processes button press interrupts and displays the values of the data1 & data2 parameters

public class Program
{
   public static void Main()
   {
      InterruptPort button = new InterruptPort(Pins.GPIO_PIN_D5, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
      button.OnInterrupt += button_OnInterrupt;

      Thread.Sleep(Timeout.Infinite);
   }

   static void button_OnInterrupt(uint data1, uint data2, DateTime time)
   {
      Debug.Print(time.ToString("hh:mm:ss.fff") + " data1 =" + data1.ToString() + " data2 = " + data2.ToString());
   }
}

Using the debugging output from this application we worked out that data1 was the Microcontroller Pin number and data2 was the button state.

12:00:14.389 data1 =24 data2 = 0
12:00:14.389 data1 =24 data2 = 1
12:00:14.389 data1 =24 data2 = 0
12:00:15.851 data1 =24 data2 = 1
12:00:16.078 data1 =24 data2 = 0

We then extended the code to record the duration of each button press.

public class Program
{
   static DateTime buttonLastPressedAtUtc = DateTime.UtcNow;

   public static void Main()
   {
      InterruptPort button = new InterruptPort(Pins.ONBOARD_BTN, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
      button.OnInterrupt += button_OnInterrupt;

      Thread.Sleep(Timeout.Infinite);
   }

   static void button_OnInterrupt(uint data1, uint data2, DateTime time)
   {
      if (data2 == 0)
      {
         TimeSpan duration = time - buttonLastPressedAtUtc;

         Debug.Print(duration.ToString());
      }
      else
      {
         buttonLastPressedAtUtc = time;
      }
   }
}

The thread ” (0x4) has exited with code 0 (0x0).
00:00:00.2031790
00:00:00.1954150
00:00:00.1962350

The next step was to keep track of the total duration of the button presses since the program started executing.

public class Program
{
   static DateTime buttonLastPressedAtUtc = DateTime.UtcNow;
   static TimeSpan buttonPressedDurationTotal;

   public static void Main()
   {
      InterruptPort button = new InterruptPort(Pins.ONBOARD_BTN, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
      button.OnInterrupt += button_OnInterrupt;

      Thread.Sleep(Timeout.Infinite);
   }

   static void button_OnInterrupt(uint data1, uint data2, DateTime time)
   {
      if (data2 == 0)
      {
         TimeSpan duration = time - buttonLastPressedAtUtc;

         buttonPressedDurationTotal += duration;
          Debug.Print(duration.ToString() + " " + buttonPressedDurationTotal.ToString());
      }
      else
      {
         buttonLastPressedAtUtc = time;
      }
   }
}

The thread ” (0x4) has exited with code 0 (0x0).
00:00:00.2476460 00:00:00.2476460
00:00:00.2193600 00:00:00.4670060
00:00:00.2631400 00:00:00.7301460
00:00:00.0001870 00:00:00.7303330

We then added a timer to display the amount of time the button was pressed in the configured period.

public class Program
{
   static TimeSpan measurementDueTime = new TimeSpan(0, 0, 30);
   static TimeSpan measurementperiodTime = new TimeSpan(0, 0, 30);
   static DateTime buttonLastPressedAtUtc = DateTime.UtcNow;
   static TimeSpan buttonPressedDurationTotal;


   public static void Main()
   {
      InterruptPort button = new InterruptPort(Pins.GPIO_PIN_D5, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
      button.OnInterrupt += button_OnInterrupt;

      Timer periodTimer = new Timer(periodTimerProc, button, measurementDueTime, measurementperiodTime);

      Thread.Sleep(Timeout.Infinite);
   }

   static void periodTimerProc(object status)
   {
      InterruptPort button = (InterruptPort)status;

      if (button.Read())
      {
         TimeSpan duration = DateTime.UtcNow - buttonLastPressedAtUtc;

         buttonPressedDurationTotal += duration; 
      }

      Debug.Print(buttonPressedDurationTotal.ToString());

      buttonPressedDurationTotal = new TimeSpan(0, 0, 0);
      buttonLastPressedAtUtc = DateTime.UtcNow;
   }

   static void button_OnInterrupt(uint data1, uint data2, DateTime time)
   {
      if (data2 == 0)
      {
         TimeSpan duration = time - buttonLastPressedAtUtc;

         buttonPressedDurationTotal += duration;

         Debug.Print(duration.ToString() + " " + buttonPressedDurationTotal.ToString());
      }
      else
      {
         buttonLastPressedAtUtc = time;
      }
   }
}

The thread ” (0x4) has exited with code 0 (0x0).
00:00:00
00:00:00
00:00:00.2299050 00:00:00.2299050
00:00:00.1956980 00:00:00.4256030
00:00:00.1693190 00:00:00.5949220
00:00:00.5949220

After some testing we identified that the handling of button presses at the period boundaries was problematic and revised the code some more. We added a timer for the startup period to simplify the interrupt handling code.

public class Program
{
   static TimeSpan measurementDueTime = new TimeSpan(0, 0, 60);
   static TimeSpan measurementperiodTime = new TimeSpan(0, 0, 30);
   static DateTime buttonLastPressedAtUtc = DateTime.UtcNow;
   static TimeSpan buttonPressedDurationTotal;

   public static void Main()
   {
      InterruptPort button = new InterruptPort(Pins.GPIO_PIN_D5, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
      button.OnInterrupt += button_OnInterrupt;

      Timer periodTimer = new Timer(periodTimerProc, button, Timeout.Infinite, Timeout.Infinite);

      Timer startUpTImer = new Timer(startUpTimerProc, periodTimer, measurementDueTime.Milliseconds, Timeout.Infinite);

      Thread.Sleep(Timeout.Infinite);
   }

   static void startUpTimerProc(object status)
   {
      Timer periodTimer = (Timer)status;

      Debug.Print( DateTime.UtcNow.ToString("hh:mm:ss") + " -Startup complete");

      buttonLastPressedAtUtc = DateTime.UtcNow;
      periodTimer.Change(measurementDueTime, measurementperiodTime);
   }

   static void periodTimerProc(object status)
   {
      InterruptPort button = (InterruptPort)status;
      Debug.Print(DateTime.UtcNow.ToString("hh:mm:ss") + " -Period timer");

      if (button.Read())
      {
         TimeSpan duration = DateTime.UtcNow - buttonLastPressedAtUtc;

         buttonPressedDurationTotal += duration;
      }

      Debug.Print(buttonPressedDurationTotal.ToString());

      buttonPressedDurationTotal = new TimeSpan(0, 0, 0);
      buttonLastPressedAtUtc = DateTime.UtcNow;
   }

   static void button_OnInterrupt(uint data1, uint data2, DateTime time)
   {
      Debug.Print(DateTime.UtcNow.ToString("hh:mm:ss") + " -OnInterrupt");

      if (data2 == 0)
      {
         TimeSpan duration = time - buttonLastPressedAtUtc;

         buttonPressedDurationTotal += duration;

         Debug.Print(duration.ToString() + " " + buttonPressedDurationTotal.ToString());
      }
      else
      {
         buttonLastPressedAtUtc = time;
      }
   }
}

The debugging output looked positive, but more testing is required.

The thread ” (0x2) has exited with code 0 (0x0).
12:00:13 -Startup complete
12:01:13 -Period timer
00:00:00
12:01:43 -Period timer
00:00:00
12:01:46 -OnInterrupt
12:01:48 -OnInterrupt
00:00:01.2132510 00:00:01.2132510
12:01:49 -OnInterrupt
12:01:50 -OnInterrupt
00:00:01.3001240 00:00:02.5133750
12:01:53 -OnInterrupt
12:01:54 -OnInterrupt
00:00:01.1216510 00:00:03.6350260
12:02:13 -Period timer
00:00:03.6350260

Next steps – multi threading, extract code into a device driver and extend to support sensors like the SeeedStudio Smart dust Sensor which has two digital outputs, one for small particles (e.g. smoke) the other for larger particles (e.g. dust).

Netduino pollution Monitor V0.1

As part of a project for Sensing City I had been helping with the evaluation of  PM2.5/PM10 sensors for monitoring atmospheric pollution levels. For my DIY IoT projects I use the SeeedStudio Grove system which has a couple of dust sensors. The Grove Dust Sensor which is based on a Shinyei Model PPD42 Particle Sensor looked like a cost effective option.

Seeedstudio Grove Dust Sensor

Seeedstudio Grove Dust Sensor

Bill of Materials for my engineering proof of concept (Prices as at June 2015)

I initially got the sensor running with one of my Arduino Uno R3  devices using the software from the seeedstudio wiki and the ratio values returned by my Netduino Plus 2 code (see below) look comparable. I have purchased a couple of extra dust sensors so I can run the Arduino & Netduino devices side by side. I am also trying to source a professional air quality monitor so I can see how reliable my results are

The thread ” (0x2) has exited with code 0 (0x0).

Ratio 0.012

Ratio 0.012

Ratio 0.020

Ratio 0.008

Ratio 0.031

Ratio 0.014

Ratio 0.028

Ratio 0.012

Ratio 0.013

Ratio 0.018

public class Program
{
private static long pulseStartTicks = 0;
private static long durationPulseTicksTotal = 0;
readonly static TimeSpan durationSample = new TimeSpan(0, 0, 0, 30);
readonly static TimeSpan durationWaitForBeforeFirstSample = new TimeSpan(0, 0, 0, 30);

public static void Main()
{
InterruptPort sensor = new InterruptPort(Pins.GPIO_PIN_D8, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
sensor.OnInterrupt += sensor_OnInterrupt;

Timer sampleTimer = new Timer(SampleTimerProc, null, durationWaitForBeforeFirstSample, durationSample);

Thread.Sleep(Timeout.Infinite);
}

static void sensor_OnInterrupt(uint data1, uint data2, DateTime time)
{
if (data2 == 1)
{
long pulseDuration = time.Ticks - pulseStartTicks;

durationPulseTicksTotal += pulseDuration;
}
else
{
pulseStartTicks = time.Ticks;
}
}

static void SampleTimerProc(object status)
{
double ratio = durationPulseTicksTotal / (double)durationSample.Ticks ;
durationPulseTicksTotal = 0;

Debug.Print("Ratio " + ratio.ToString("F3"));
}
}

Next steps will be, adding handling for edges cases, converting the ratio into a particle concentration per litre or 0.1 cubic feet, selecting a weather proof enclosure, smoothing/filtering the raw measurements, and uploading the values to Xively for presentation and storage.