Delphi and Barcode scanning

Todays example uses a dll to access a Barcode Scanner. The used Barcode Scanner is the CS1504 (SDK available here).

The CS1504 has a buffer where it stores all scanned barcodes and this buffer can be accessed via a COM-Port. Luckily, the SDK has a dll which takes care of the communication. The only problem is, that the header is written in C/C++. I translated it (in parts) to Delphi, you can grab the file here.

Now we could just use it as is, but it would be much nicer if we had a class to wrap it all up.

We need some object to store the data, which is really simple:

TBarcode = class
  private
    fTimestamp : TDateTime;
    fCode : string;
  public
    constructor Create(aTimestamp : TDateTime; aCode : string);
    property TimeStamp : TDateTime read fTimestamp;
    property Code : string read fCode;
  end;

And now the class that does all the work:

TScanner = class
  private
    fPort : integer;
    fReady : boolean;
    fHasData: boolean;
    function TimestampToDateTime(aTimestamp : Ansistring) : TDateTime;
  public
    constructor Create(aPort : integer);
    destructor Destroy; override;
    function getBarcodes : TList<TBarcode>;
    procedure clearBarcodes;
    property IsReady : boolean read fReady;
    property HasData : boolean read fHasData;
    procedure setDateTime(aDateTime : TDateTime);
    function getDateTime : TDateTime;
  end;

The TScanner class returns a generic TList<TBarcode> with all the Barcodes from the device.

The most important function is of course getBarcodes.

function TScanner.getBarcodes: TList<TBarcode>;
var
  bc : TBarcode;
  i, count, pl : integer;
  buffer : array[0..63] of AnsiChar;
  dt : TDateTime;
  s : string;
begin
  result := TList<TBarcode>.Create;
  begin
    count := csp2ReadData;
    for i := 0 to count -1 do
    begin
      FillChar(buffer,64,#0);
      pl := csp2GetPacket(@buffer,i,63);

      // The Last 4 Bytes hold the timestamp
      dt := TimestampToDateTime(copy(buffer,pl-3,4));

      s := copy(buffer,3,pl-6);
      bc := TBarcode.Create(dt,s);
      result.Add(bc);
    end;
  end;
end;

The implementation is pretty much straight forward, the trickiest part was to convert the 4-byte timestamp from each barcode to TDateTime. They crammed the six values for year, month, day, hour, minute and second into 4 bytes. (seriously, a SD Card that has the size of my fingernail can hold easily 4 GB and they worry about 2 bytes per scanned barcode)

function TScanner.TimestampToDateTime(aTimestamp: Ansistring): TDateTime;
var
  i1,i2,i3,i4,i5,i6 : integer;
  qb : T4Bytes;
  y,m,d,h,n,s : word;
begin
  // CharToByte
  qb.Bytes[3] := Ord(aTimestamp[1]);
  qb.Bytes[2] := Ord(aTimestamp[2]);
  qb.Bytes[1] := Ord(aTimestamp[3]);
  qb.Bytes[0] := Ord(aTimestamp[4]);

  // split up the bits
  i1 := qb.Total and $fc000000; // 6 Bit
  i2 := qb.Total and $03f00000; // 6 Bit
  i3 := qb.Total and $000f8000; // 5 Bit
  i4 := qb.Total and $00007c00; // 5 Bit
  i5 := qb.Total and $000003c0; // 4 Bit
  i6 := qb.Total and $0000003f; // 6 Bit

  // Shift right to align the bits
  s := i1 shr 26;
  n := i2 shr 20;
  h := i3 shr 15;
  d := i4 shr 10;
  m := i5 shr 6;
  y := i6;

  result := EncodeDate(y+2000,m,d) + EncodeTime(h,n,s,0);
end;

This uses T4Bytes which is a packed record.

T4Bytes = packed record
   case Integer of
    0: (Bytes: array[0..3] of Byte);
    1: (Total: Cardinal);
  end;

The bytes are accessible indivudually and as the resulting 4-Byte Cardinal.

Full Sourcecode is available here.