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Introduction

In my first article using the Arduino 2009 board, I described a simple temperature sensor interfaced using Visual Basic.

I have developed the board and Visual Basic code to give a fairly usable indoor weather station.

Overall Operation

The Arduino 2009 acts as a standalone weather station. It does not display the data. It can operate independently for months. It samples the sensors until the RAM is full. The RAM samples are stored on a sector of an SD card. Eventually, a year's weather samples could be stored on the SD card.

Each time the PC is connected, any unstored sectors are uploaded to files on the PC's hard drive. It can then be displayed using all the facilities of the PC's display.

The central idea is that the PCc has a file copy of each SD card sector stamped with the date time it was recorded.

Arduino Indoor Weather Station

The activity diagram for the program:

The Arduino IDE uses C++, and the actual program for this activity diagram is straightforward.

The SD card current sector is held in EEPROM so that during power off or reset, it can be reused. The Arduino has a class EEPROM which only allows read and write of bytes. To read a long (32 bytes in Arduino) requires some work:

inline void ready()
{
  unsigned long lastblock = 0;  //the last block number saved in the sd card
  unsigned long tempblock = 0;
  tempblock = EEPROM.read(0);  // remember the LSB of the last saved block
  lastblock |= tempblock;
  tempblock = EEPROM.read(1);  // remember the next LSB of the last saved block
  lastblock |= tempblock << 8;
  tempblock = EEPROM.read(2);  // remember the next LSB of the last saved block
  lastblock |= tempblock << 16;
  tempblock = EEPROM.read(3);  // remember the next MSB of the last saved block
  lastblock |= tempblock << 24;
  Serial.println("ready");  //send computer the ready to reset message
  Serial.println(lastblock);  //send computer the last saved block number
  delay(10000);  //every 10 seconds 
}//end of ready

The Arduino does not have a class to read and write to SD cards, so I wrote my own. This is the .h file:

/* Card type: Ver2.00 or later Standard Capacity SD Memory Card
              1.0 and 2.0 GB cards purchased in 2009 work well.
   Usage:  Must have global variable. 
              volatile unsigned char buffer[512];
           Function calls.
              unsigned char error = SDCARD.readblock(unsigned long n);
              unsigned char error = SDCARD.writeblock(unsigned long n);
            error is 0 for correct operation
            read copies the 512 bytes from sector n to buffer.
            write copies the 512 bytes from buffer to the sector n.
   References: SD Specifications. Part 1. Physical Layer Simplified Specification
               Version 2.00 September 25, 2006 SD Group.
               http://www.sdcard.org
   Code examples:  http://www.sensor-networks.org/index.php?page=0827727742
                   http://www.avrfreaks.net   search "sd card"
   Operation:  The code reads/writes direct to the sectors on the sd card.
               It does not use a FAT. If the card has been formatted the
               FAT at the lowest sectors and files at the higher sectors
               can be written over.
               The card is not damaged but will need to be reformatted at 
               the lowest level to be used by windows/linux.
   Timing:  readblock or writeblock takes 44 msec.
   Improvement: Could initialize so that can use version 1 sd and hc sd.
                Instead of CMD1 need to use CMD8, CMD58 and CMD41.
*/
#ifndef SDCARD_h
#define SDCARD_h
#define setupSPI SPCR = 0x53; //Master mode, MSB first,
                              //SCK phase low, SCK idle low, clock/64
#define deselectSPI SPCR = 0x00;  //deselect SPI after read write block
#define clearSPI  SPSR = 0x00; // clear SPI interrupt bit
#define setupDDRB DDRB |= 0x2c;  //set SS as output for cs
#define selectSDCARD PORTB &= ~0x04;  //set the SS to 0 to select the sd card 
#define deselectSDCARD PORTB |= 0x04;  //set the SS to 1 to deselect the sd card 
#include "WProgram.h"
class SDCARDclass
{
public:
    unsigned char readblock(unsigned long Rstartblock);
    unsigned char writeblock(unsigned long Wstartblock);
private:
    unsigned char SD_reset(void);
    unsigned char SD_sendCommand(unsigned char cmd, unsigned long arg);
    unsigned char SPI_transmit(unsigned char data);
};//end of class SDCARDclass
extern SDCARDclass SDCARD;
#endif

So, when we need to save a sector of data, we do:

inline void lastblocksave()
{
   unsigned int e = 0;  //the error code from the sd card
   e = SDCARD.writeblock(currentblock);  //save this 256 block of integer data 
   while (e != 0)   //cant continue if sd card not working
   {
       Serial.println("writesderror");  //send computer sd card error
       Serial.println(e);  //send computer the error number
       digitalWrite(8, HIGH);  //turn led on to show sd card error
       delay(10000);  //every 10 seconds
   }//end of sd card not working
   currentblock +=1;  //go to the next block in sd card
   EEPROM.write(0,currentblock);  //write the LSB of saved block to EEPROM
   EEPROM.write(1,currentblock >> 8);  //write the next LSB of saved block to EEPROM
   EEPROM.write(2,currentblock >> 16);  //write the next LSB of saved block to EEPROM
   EEPROM.write(3,currentblock >> 24);  //write the MSB of saved block to EEPROM      
   ramaddress = 0;   //we can now start again to save samples in RAM        
}//end of sd save

PC Program Startup

The PC program was written using Microsoft's Visual Basic Express IDE.

When the display program loads and before it is activated, we create a startup form which has all the routines to upload the data samples.

Private Sub ArduinoWeather_Load(ByVal sender As System.Object, _
            ByVal e As System.EventArgs) Handles MyBase.Load
    Dim f As New showstart
    f.ShowDialog()  'startup form to connect to arduino
    While My.Computer.FileSystem.FileExists(cd & "\" & last_sector)
        last_sector += 1 'find the next block
    End While   
    If My.Computer.FileSystem.FileExists(cd & "\archive") Then
        Dim st As Stream = File.Open(cd & "\archive", FileMode.Open, FileAccess.Read)
        Dim br As New BinaryReader(st)  'to get samples from stream
        Try
            Dim n As Integer = 0  'a counter
            Do
                archived(n) = br.ReadInt64()
                archivedisplay.Items.Add(archived(n))
                If archived(n) > lastblock Then lastblock = archived(n)
                n += 1  'we get the largest archive block
                If n = 100 Then Exit Do 'no more room
            Loop
        Catch ex As Exception  'exception of none left
        Finally
            br.Close()   'must close
            st.Close()
        End Try  'exit try when all read
    End If
    fill_buffers() 'get all the samples into thir buffers
    If overflow.Text = "" Then  'enable displays
        Try
            com8 = My.Computer.Ports.OpenSerialPort("com8", 9600)
            readthread = New Threading.Thread(AddressOf read)
            readthread.Start()  'thread runs for whole program 
                                'to get samples every 10 sec
        Catch ex As Exception
            comdisplay.Text = "no connection" & vbNewLine & _
                              "or" & vbNewLine & "no communication"
            display_noconnect.Enabled = True  'just use a timer to display
        End Try
    End If
End Sub

The activity diagram for the start form is shown here:

The whole purpose of this startup is to ensure that every sector on the SD card is recorded on the hard drive with its real sample time. I start a thread which is used to upload any required data. This following code is the core of the procedure:

Dim st As Stream = File.Open(save_sd, FileMode.Create, FileAccess.Write)
Dim bw As New BinaryWriter(st)  'to send samples to stream
For i = 0 To 255  'all old samples
    bw.Write(sd_samples(i))  'send all the samples
Next  'sector stored in file
bw.Write(date_stamp.ToString("F"))  'add date to file
date_stamp = date_stamp.Add(TimeSpan.FromSeconds(850))
bw.Close()   'sends all samples to file
st.Close()
lastblock = j 'we have uploaded one sector
upload = "uploading"
Invoke(New messdelegate(AddressOf showmessage)) 'show the progress

The user will see a form center screen:

Next, in the user form load, we determine the number of sector files. Then, the archived files are stored in their own file. We then fill the display buffers from the relevant sector files.

Finally, we start a thread which will read the new data samples that will be displayed in the current display.

At last, the user form is displayed:

PC Program User Form

The display images are generated in its own class. The data is passed to the class and then the image is added to the user form. If the display is as detailed as possible, i.e., each 10 second sample has its own pixel, the full display span will be for 4 hours. The data can be averaged to give a maximum of 4 weeks per display span.

The start time of the display can be offset to allow a view of any section of the 4 weeks data. This can be at the maximum resolution (10 sec. per sample).

This code implements the operation:

Private Sub display_all()
    Try
        Dim Tinterrim_buffer(241919) As Int32  'interim buffer for temperature display
        Dim Hinterrim_buffer(241919) As Int32  'interim buffer for humidity display
        Dim Ainterrim_buffer(241919) As Int32  'interim buffer for air pressure display
        Dim Cdisplay_start_time As DateTime  'the current display start time
        Select Case True
            Case RadioButton1.Checked
                display_span = span_define(0)  '4 hours
            Case RadioButton2.Checked
                display_span = span_define(1)  '8 hours
            Case RadioButton3.Checked
                display_span = span_define(2)  '12 hours
            Case RadioButton4.Checked
                display_span = span_define(3)  '24 hours
            Case RadioButton5.Checked
                display_span = span_define(4) '2 days
            Case RadioButton6.Checked
                display_span = span_define(5)  '4 days
            Case RadioButton7.Checked
                display_span = span_define(6) '7 days
            Case RadioButton8.Checked
                display_span = span_define(7)  '2 weeks
            Case RadioButton9.Checked
                display_span = span_define(8)  '4 weeks
        End Select
        For i = 0 To 241919
            If i < last_pointer + 1 Then
                Tinterrim_buffer(241919 - i) = temp_buffer(last_pointer - i)
                Hinterrim_buffer(241919 - i) = humid_buffer(last_pointer - i)
                Ainterrim_buffer(241919 - i) = air_buffer(last_pointer - i)
            Else
                Tinterrim_buffer(241919 - i) = 999999
                Hinterrim_buffer(241919 - i) = 999999
                Ainterrim_buffer(241919 - i) = 999999
            End If
        Next
        d.display_span_time = TimeSpan.FromMinutes(240 * display_span)
        Dim number_display As Integer = _
        1440 * display_span - 1  'the width of current span
        If cursor_time + number_display < 241920 Then
            Cdisplay_start_time = display_start_time.AddDays(-28 * cursor_time / 241919)
            Dim counter As Integer = 0
            For i = 241919 - cursor_time To 0 _
            Step -display_span  'copy working to display
                Dim average = 0
                For j = 0 To display_span - 1
                    average += Tinterrim_buffer(i - j)
                Next  'straight average of the number of samples required
                d.temperature(1439 - counter) = average / display_span
                average = 0
                For j = 0 To display_span - 1
                    average += Hinterrim_buffer(i - j)
                Next  'straight average of the number of samples required
                d.humidity(1439 - counter) = average / display_span
                average = 0
                For j = 0 To display_span - 1
                    average += Ainterrim_buffer(i - j)
                Next  'straight average of the number of samples required
                d.airpressure(1439 - counter) = average / display_span
                counter += 1 'we have done one
                If counter = 1440 Then Exit For
            Next
        Else
            hasbeenoffset.Text = "selected offset out of range"
            cursor_time = 0 'reset the value
        End If
        d.display_start_time = Cdisplay_start_time
        If zoom_TH Or zoom_AR Then
            If zoom_TH Then
                d.full_temp_hum() 'expand temp humid
            Else
                d.full_air_rain()   'expand air rain
            End If
        Else  'normal display
            d.scale_temp_hum()
            d.scale_air_rain()
        End If
    Catch ex As Exception
    End Try
End Sub

The user form can start a file management form:

Here is the code to archive a file:

Private Sub archivefile_Click(ByVal sender As System.Object, _
            ByVal e As System.EventArgs) Handles Button5.Click
    If My.Computer.FileSystem.FileExists(cd & "\archive") Then
        Dim words() As String = archived.Text.Split(vbNewLine)
        Dim x = CLng((words.Length - 1))
        If archiveblock > CLng(words(words.Length - 2)) + 100 Then
            Dim str As Stream = File.Open(cd & "\archive", _
                                          FileMode.Append, FileAccess.Write)
            Dim bwr As New BinaryWriter(str)  'to send samples to stream
            bwr.Write(archiveblock)  'send all the samples to disk
            bwr.Close()   'sends all samples to file
            str.Close()
        Else
            MsgBox("The archived block must be at least" & vbNewLine & _
                   "one day -that is 100 bigger than last")
        End If
        Dim st As Stream = File.Open(cd & "\archive", FileMode.Open, FileAccess.Read)
        Dim br As New BinaryReader(st)  'to get samples
        archived.Text = ""
        Try
            Do
                archived.Text = archived.Text & (br.ReadInt64()) & vbNewLine
            Loop
        Catch ex As Exception  'exception of none left
        Finally
            br.Close()   'must close
            st.Close()
       End Try  'exit try when all read
    End If
End Sub

Circuit diagram for weather station:

Indoor Weather Station using Arduino