Netduino and VB are cool... as shown in this Tempature Monitoring project

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Today's Hardware Friday post provides a working example of using Visual Basic in a Netduino based project.

Temperature Monitoring using VB.Net, Micro-framework and a Netduino


That’s when I saw this little device called the Netduino which runs something called the .NET Micro-framework. This seems just what I’ve been looking for. A microcontroller device that I can put together a few electronics items which are available off-the-shelf and write some .NET code in my language of choice (VB) to implement some basic functionality.

So the next question is what did I think would be a good first project?

My wife is studying to be a sommelier which means we have quite a few bottles of wine in the house. Sometimes we open one up an it’s developed a fault. Now there are numerous reasons for wines developing faults but incorrect storage is one possible cause. Wine is very temperamental and is best stored in a cool dark climate that doesn’t change much through the seasons which is why cellars or caves are great for storage but unfortunately in normal modern houses a cave or wine cellar is not a standard item. So we use our pantry to store our wine.

With this in mind I wanted to be able to know if the pantry conditions were really fluctuating that much. So I had my project but where to start? A simple device to monitor the wine cellar (eer pantry!!!) and provide warning indications of hi or low temperature conditions


The applicable needs to do a number of tasks

  • · Read the sensors
  • · Write the data to the SD Card
  • · Detect any temperature warning conditions.
  • · Provide visual indications of working and warning conditions
  • · Provide a reset capability

My approach was to take each task and build an evolving system. So the first thing was to wire up the sensor and the LED’s. Using a breadboard makes it real easy and is really a case of plugging wires in to make the connections.

The design looked like the following. It looks a bit crazy when prototyping but I’ll eventually clean this up before putting the item in the pantry and having a worried wife come tell me there is a mysterious device with wires coming out of it in the pantry.




Reading the sensor

The code for this application is a simple Console application which is running indefinitely. As I’m powering the final device by means of a 9v battery I want to do enough to get the job done but want to make sure that I have sufficient battery life. So I will be taking a reading every 10 minutes which means that most of the time the device is really asleep.

There are both analogue and digital temperature sensors. Mine original sensor is a simple thermistor (Temperature dependent resistor) which means that the resistance varies with temperature changes. Using the Analogue input ports on the Netduino in conjunction with this allows me to determine a temperature. There are two revisions of the Netduino (Rev A and Rev B). The significant difference between the two is related to Analogue references and the need to provide an extra link between the 3.3v pin and the Aref0 pin – without this the values read on the Analogue port will be inconsistent. Luckily almost all boards out there are Rev B boards with this already internally connected on the board preventing you from having to remember this.

The formula for calculating a temperature is as follows….

Imports Microsoft.SPOT
Imports Microsoft.SPOT.Hardware
Imports SecretLabs.NETMF.Hardware
Imports SecretLabs.NETMF.Hardware.Netduino

Public Module Module1
    Dim PollingDelay As Integer = 2
    Dim tempSensor As New AnalogInput(Pins.GPIO_PIN_A5)
    Dim CurrentTemperature As Double = 0

    Public Sub Main()
        Dim Temperature As Double = 0

        '//Setup Event Handlers

        '//Get the initial temperature
        CurrentTemperature = GetAverageTemperatureReading()
        While True
        End While
    End Sub

   Function GetCurrentTemperature() As Double
        ''Read the raw sensor value
        Return tempSensor.Read()
    End Function

    'Get the average temperature of 101 readings over a second
    Function GetAverageTemperatureReading() As Double
        Dim totalTemp As Double
        Dim averagetemp As Double = 0

        For i = 0 To 99
            totalTemp += GetCurrentTemperature()
        averagetemp = totalTemp / 100

        Dim Kelvin As Double = (((averagetemp / 1023) * 3.3) * 100)
        Dim Celsius As Double = (Kelvin - 273) - 17.8
        Dim Fahrenheit = (Celsius) * (9 / 5) + 32

        Debug.Print(WarningStatus.ToString & " " & averagetemp.ToString() & " " & Fahrenheit.ToString & " / " & Celsius.ToString & " ")

        Return Celsius
    End Function

    Private PollingTimer As Timer

    Private Sub PollingTemperatureMethod()
        Dim PollingDelegate As New TimerCallback(AddressOf PollForTemperature)
        PollingTimer = New Timer(PollingDelegate, Nothing, 1000, PollingDelay * 1000)
    End Sub

    Public Sub PollForTemperature(stateInfo As Object)
        Module1.CurrentTemperature = GetAverageTemperatureReading()
    End Sub

End Module

Detecting Warning Conditions

I wanted my code to be able to detect hot and cold warning conditions as both of these can cause problems with wine storage. During development I wanted a much narrower temperature range allowing me to trigger it easily but chose to read these settings into the application from a file on the SD Card to make it flexible. Allowing me modify the settings without having to redeploy the application. Once I have these Maximum and Minimum values I can then use these to determine if the sensor reading is a Warning Condition and if this has occurred turn on one of the two warning LED to provide a clear indication that we have had an temperature event occur.

Dim HiWarningLED As New OutputPort(Pins.GPIO_PIN_D9, False)
Dim LowWarningLED As New OutputPort(Pins.GPIO_PIN_D11, False)

Public Enum LevelCheck
End Enum

    Dim LowWarningStatus As Boolean = False
    Dim WarningStatus As Boolean = False
    Dim MinTemp As Single = 20
    Dim MaxTemp As Single = 26

    Function CheckTemperatureForWarning(Temp As Double, Optional Level As LevelCheck = LevelCheck.HiTemp) As Boolean
        Dim WarnStateOccured As Boolean = False
        If Level = LevelCheck.LowTemp Then
            'Is Temperature Exceeding MaxTemp
            If Temp <= MinTemp Then
                Debug.Print("Low Warning Triggered")
                Debug.Print("Temp: " & Temp.ToString)
                Debug.Print("maxTemp: " & MaxTemp.ToString)
                Debug.Print("minTemp: " & MinTemp.ToString)
                WarnStateOccured = True
            End If
        ElseIf Level = LevelCheck.HiTemp Then
            'Is Temperature Exceeding MaxTemp
            If Temp >= MaxTemp Then
                Debug.Print("Hi Warning Triggered")
                Debug.Print("Temp: " & Temp.ToString)
                Debug.Print("maxTemp: " & MaxTemp.ToString)
                Debug.Print("minTemp: " & MinTemp.ToString)
                WarnStateOccured = True
            End If
        End If
        Return WarnStateOccured
    End Function

    Sub WarningStatusLight(State As Boolean, Optional Level As LevelCheck = LevelCheck.HiTemp)
        'Code to turn on/off LED
        If Level = LevelCheck.LowTemp Then LowWarningLED.Write(State)
        If Level = LevelCheck.HiTemp Then HiWarningLED.Write(State)
    End Sub

Public Sub PollForTemperature(stateInfo As Object)
        Module1.CurrentTemperature = GetAverageTemperatureReading()

        'If the warning status light is off and a warning temperature occurs then 
        'set Warning Light State to True and don't bother checking any more as the 
        'alarm condition has been met
        If LowWarningStatus = False AndAlso CheckTemperatureForWarning(CurrentTemperature, LevelCheck.LowTemp) = True Then
            LowWarningStatus = True
            WarningStatusLight(LowWarningStatus, LevelCheck.LowTemp)
        End If

        If WarningStatus = False AndAlso CheckTemperatureForWarning(CurrentTemperature, LevelCheck.HiTemp) = True Then
            WarningStatus = True
            WarningStatusLight(WarningStatus, LevelCheck.HiTemp)
        End If
End Sub


I now have a basic functioning sensor that I can used to retrieve sensor readings from my Wine Cellar which will give me a visual indication of spoilage temperature conditions. I’ve managed to read a build a circuit, read a sensor, use timers to poll for reading, turn on/off LED’s for Visual Indication, Interact with device via a button input and write data to a Micro SD Card. These are basic functions which can be used over and over again in many different applications.

The idea is that it's not hard to get started playing with Netduino, and if you're a C#'er or a VB, the .Net Micro Framework is speaks in your language...


Here’s a few more links you might find interesting:


Page image,arct0405, courtesy of NOAA Photo Library

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