One way to achieve a smooth needle movement is to
continuously modify the velocity based on the
distance the needle has to move. The larger the
distance, the shorter the time interval between
steps.

You would constantly compare the present position
with the desired position. The absolute value of the
difference would be used to govern the current
step rate. The sign of the difference would be used
to determine the direction of the step.

In pseudo-code the procedure would be something like this:

Initialization:
   Home stepper motor to 0 position
   Clear CurrentValue to 0
   Set Direction to UP
   Set TargetValue to 0
   Set Difference to 0

StepperMeter: (Main Routine)
   Call GetTargetValue. <TargetValue now has 8 bit value>.
   Call FindDifference. <Difference and Direction are now loaded>
   Call OneStep. <Step ONCE UP/DOWN and update CurrentValue>
   Call FindDifference. <New Difference and Direction now loaded>
   Call DelayDifference. <Delay based on remaining difference>
   Goto StepperMeter. <Loop>

GetTargetValue: (Subroutine)
   Check availability of new value.
   IF nothing new to be acquired THEN Return. ENDIF
   Acquire TargetValue via ADC/SerialPort, or via
    other means.
   Convert TargetValue into 8 bit form if not already
    received in this form. <8 bit unsigned binary.>
   Return with 8 bit value in TargetValue.

FindDifference: (Subroutine)
   Compare TargetValue and CurrentValue

   IF TargetValue=CurrentValue
    THEN set Difference to 0
         set Direction to UP
         Return.
   ENDIF

   IF TargetValue>CurrentValue
    THEN set Difference to TargetValue-CurrentValue
         set Direction to UP
         Return
   ENDIF

   IF CurrentValue>TargetValue
    THEN set Difference to CurrentValue-TargetValue
         set Direction to DOWN
         Return
   ENDIF

OneStep: (Subroutine)
   IF Difference=0 THEN Return. ENDIF

   IF Direction=UP
    THEN step up once
         decrement Difference
         Return
   ENDIF

   IF Direction=DOWN
    THEN step down once
         decrement Difference
         Return
   ENDIF

DelayDifference: (Subroutine)
   IF Difference=0 THEN Return. ENDIF

  Compute number of extra delay units: Units=255-Difference
  IF Units=0 THEN Set Units to 1 ENDIF

  Call StepTime (minimum step time)
DelayLoop:
  Call IttyBittyTime
  Decrement Units
  IF Units>0 THEN Goto DelayLoop ENDIF

  Return

StepTime: (Subroutine)
  Delay for 5 milliseconds (or whatever min step time is)
  Return

IttyBittyTime: (Subroutine)
  Delay for 100 microseconds (experiment with this value)
  Return

**************

Fr. Tom McGahee