There are several methods of controlling a stepper motor from a computer. The simplest method is to use a direct connection to the parallel port, as shown in the schematic to the right.
Each of the four lines from the parallel port (pins 2, 3, 4 and 5) are used to switch an NPN power transistor that controls a coil in the motor. The transistors are protected from excessive current flow by the 1k resistors, and they are protected from the coils' backlash current by the shorting diodes.
All the parts needed to build this simple circuit are available at Radio Shack, but be aware that Radio Shack's prices for components are literally quadruple that of other electronics stores.
|NPN pwr. transistor||10W||4||4 x 276-2017|
|Diode||1A||4||2 x 276-1102|
The following BASIC program demonstrates how to drive the motor from the computer. It will run a stepper motor at any speed in either direction.
10 REM Stepper Motor Controller 20 PORT = &H3BC 30 STATE = STATE + DIRECTION 40 IF STATE > 4 THEN STATE = 1 50 IF STATE < 1 THEN STATE = 4 60 PRINT STATE, 70 IF STATE = 1 THEN OUT PORT, 3: REM 1100 80 IF STATE = 2 THEN OUT PORT, 6: REM 0110 90 IF STATE = 3 THEN OUT PORT, 12: REM 0011 100 IF STATE = 4 THEN OUT PORT, 9: REM 1001 110 FOR W = 1 TO DELAY: NEXT W 120 X$ = INKEY$ 130 IF X$ = "<" THEN DIRECTION = -1: REM Backwards 140 IF X$ = ">" THEN DIRECTION = 1: REM Forwards 150 IF X$ = "?" THEN DIRECTION = 0: REM Stop-locked 160 IF X$ = "-" THEN DELAY = DELAY + 100: REM Slow down 170 IF X$ = "+" THEN DELAY = DELAY - 100: REM Speed up 180 IF X$ <> CHR$(27) THEN GOTO 30 190 OUT PORT, 0: REM 0000 (Stop-free)
Up to three stepper motors may be attached to one parallel port in this manner. The second motor would be connected to the other half of the data register (pins 6, 7, 8 and 9). The third motor would use the parallel port's control register (pins 1, 14, 16 and 17).