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Designing the software data logger for MASTECH MS8229

Let's talk in "object oriented" way but we apply a non class based approach in order to be easier to understand.
Let's call our approach "object based" even if this is not 100% correct.
We will write our code in Object Pascal using Lazarus, later we will try to port the project in Linux and MacOSX.

A multimeter has a code and a status.

The code has a 14 byte value and can be valid or not.

From the table of our multimeter we can find the attributes which characterize it's status.

  • IsRS232:boolean;  //The multimeter can have RS232 on or off
  • IsAuto:boolean;   //auto can be on or off
  • AC_DC_None : TAC_DC_None;  //this can have values AC, DC and None
  • ValueNoPrefix : string; //Value without prefix
  • UnitValue : string; //Unit value : Ohm Hz V A F
  • UnitPrefix : string; //Prefix : K,M,n,u,m
  • ValuePrefix : string; //Value with prefix
  • IsDiode : boolean; //The diode mode is on or off
  • IsSound: boolean; //The continuity mode is on or off
  • IsRelative : boolean; //The relative sign is on or off
  • IsHold : boolean;  //The hold sign is on or off
  • IsBattery : boolean;   //The battery sign is on or off


So the code below is fully understandable :

  TAC_DC_None = (AC, DC, None);

  TStatus = record
    AC_DC_None : TAC_DC_None;
    ValueNoPrefix : string; //Value without prefix
    UnitValue : string; //Ohm Hz V A F
    UnitPrefix : string; //K,M,n,u,m
    ValuePrefix : string; //Value with prefix
    IsDiode : boolean;
    IsSound: boolean;
    IsRelative : boolean;
    IsHold : boolean;
    IsBattery : boolean;

type TCode = record
  Value : array [0..13] of byte; //14 bytes
  IsValid : boolean;

  TMultimeter = record
    Code : TCode;
    Status : TStatus;

Notice how easily can program if you define well your working environment !
Pretty easy don't you think ?
Always ask yourself ... does my structure define all of my working environment ?
The answer here is yes this structure defines completely the status of our multimeter.

Notice that when the multimeter shows 2KOhms we have

    ValueNoPrefix = 2000
    UnitValue = Ohm
    UnitPrefix = K
    ValuePrefix = 2

So in order to write correctly the value we can do ValueNoPrefix + UnitValue = 2000Ohm
Or alternatively ValuePrefix + UnitPrefix + UnitValue = 2KOhm

We define as : My_Multimeter : TMultimeter;

Once defined our structure we pass at the code validation.
A valid code is 1X 2X 3X 4X 5X 6X 7X 8X 9X AX BX CX DX EX so we ignore the 4 last bits of each byte.
To do so we use the shift right technique : XXXXYYYY shr 4 -> 0000XXXX

function TFormMain.IsValidCode():boolean;

  result := false;
  if (My_Multimeter.Code.Value[0] shr 4 = 1) and
     (My_Multimeter.Code.Value[1] shr 4 = 2) and
     (My_Multimeter.Code.Value[2] shr 4 = 3) and
     (My_Multimeter.Code.Value[3] shr 4 = 4) and
     (My_Multimeter.Code.Value[4] shr 4 = 5) and
     (My_Multimeter.Code.Value[5] shr 4 = 6) and
     (My_Multimeter.Code.Value[6] shr 4 = 7) and
     (My_Multimeter.Code.Value[7] shr 4 = 8) and
     (My_Multimeter.Code.Value[8] shr 4 = 9) and
     (My_Multimeter.Code.Value[9] shr 4 = 10) and
     (My_Multimeter.Code.Value[10] shr 4 = 11) and
     (My_Multimeter.Code.Value[11] shr 4 = 12) and
     (My_Multimeter.Code.Value[12] shr 4 = 13) and
     (My_Multimeter.Code.Value[13] shr 4 = 14) then
       result := true;