program to drive 3 phase hard drive stepper

[Chris]

here is something ive been working on that i think some people may find useful. this program will drive a 3 phase stepper motor (the one i used was from a laptop hard drive) without the use of hall effect sensors (it starts in a blind open loop, until its fast enough to read the back electromotive force). ive gotten this program to drive the motor at least 7,000 rpm in open loop mode, and is very stable in closed loop, it will reset back to open loop if the motor stalls. if anyone has any questions, such as where the pins go to what ( i think ive labeled them as constants and comments pretty well) just ask and ill answer. this is a contribution to give back for all the help ive gotten on this forum before, hope you enjoy.
oh and by the way this code is meant to run on an 11input/output (7 used 3 of which are ANALOG and 4 are OUTPUTS) 16f616

;Chip Settings
#chip 16F616,8
#config BOD=OFF, BOR=OFF, OSC=INTRC_OSC_NOCLKOUT, MCLRE=OFF
;Defines (Constants)
#define phase_a portc.5
#define phase_b portc.4
#define phase_c portc.3
#define phase_locked_led porta.2
;Variables
Dim milli_seconds As byte
Dim locked As bit
Dim step_sequence As byte
Dim phase_in As byte
Dim timer_temp As word
Dim micro_seconds As word
;Interrupt Handlers
On Interrupt Timer0Overflow Call timer0_overflow
On Interrupt Timer1Overflow Call open_loop_ramp
InitTimer1 Osc, PS1_1/8
StopTimer 1
ClearTimer 1
InitTimer0 Osc, PS0_1/64
open_loop_ramp
Dir PORTC.0 In
Dir PORTC.1 In
Dir PORTC.2 In
Do Forever
    step_sequence = 1
    Dir phase_b Out
    Dir phase_a In
    Set phase_b Off
    Set phase_c On
    check_cross
    step_sequence = 2
    Dir phase_a Out
    Set phase_a On
    Set phase_b Off
    Dir phase_c In
    check_cross
    step_sequence = 3
    Dir phase_c Out
    Set phase_a On
    Dir phase_b In
    Set phase_c Off
    check_cross
    step_sequence = 4
    Dir phase_b Out
    Dir phase_a In
    Set phase_b On
    Set phase_c Off
    check_cross
    step_sequence = 5
    Dir phase_a Out
    Set phase_a Off
    Set phase_b On
    Dir phase_c In
    check_cross
    step_sequence = 6
    Dir phase_c Out
    Set phase_a Off
    Dir phase_b In
    Set phase_c On
    check_cross
Loop
Sub timer0_overflow
    If milli_seconds=0 Then
        locked = 1
        Exit Sub
    End If
    micro_seconds = micro_seconds-1
    If micro_seconds=0 Then
        If milli_seconds>0 Then
            micro_seconds = 99
            milli_seconds = milli_seconds-1
        End If
    End If
End Sub
Sub check_cross
    phase_in = 250
    If locked=1 Then
        Set phase_locked_led On
        ClearTimer 1
        startTimer 1
        Do Until phase_in<200 or locked=0
            'the part of the sequence where B is input
            If step_sequence=3 or step_sequence=6 Then
                'read phase A
                phase_in = readAD(an4)
            End If
            'the part of the sequence where C is input
            If step_sequence=2 or step_sequence=5 Then
                'read phase B
                phase_in = readAD(an5)
            End If
            'the part of the sequence where A is input
            If step_sequence=1 or step_sequence=4 Then
                'read phase C
                phase_in = readAD(an6)
            End If
        Loop
        StopTimer 1
        timer_temp = Timer1
        ClearTimer 1
        startTimer 1
        Wait Until Timer1<=timer_temp or locked=0
        StopTimer 1
    End If
    If locked=0 Then
        Wait milli_seconds ms
        Wait micro_seconds 10us
    End If
End Sub
Sub open_loop_ramp
    Set phase_locked_led Off
    micro_seconds = 99
    milli_seconds = 20
    locked = 0
End Sub

[Nobody/Anonymous]

Fascinating! 
I have a couple of questions…
How would you set it to give a fixed rpm?
Are you driving the motor direct from the 16F616 pins?
I thought that these motors require 12V and quite a bit of current. 
I have been using a L6232B to bump up the current and voltage, but it complicates things quite a bit and it gets alarmingly hot at high rpm.