Driving a uni-polar stepper motor with the

SAA 1027 stepper motor driver

I found the SAA 1027 IC in my junk box and thought it would make an interesting project. It is a fairly early and hence simple chip. It drives the stopper motor in only one mode and the only control functions available are direction and reset.

This has of course some advantages, because it means that - ignoring the reset - the stepper motor can be driven using only two output lines. If one were to use the analogue outputs as well as the digital outputs, 5 stepper motors could be controlled using just one Velleman interface board. The circuit diagram below shows the simplicity of the set-up. Notice pin 4. The resistor connected to it determines the base current of the driver transistors and it should be adjusted to fit the type of motor you use. Be also aware that the SAA 1027 only starts working at around 8V, so 6V stepper motors are out of the question.

Additionally, the motor will always draw power - there is no way to shut the power off while the rotor is stationary. Apart from this, the circuit works well and uses only two output lines.

Suggested PCB layout. The Velleman side is on the left and motor and power connections on the right.

The program

Because the SAA1027 does most of the work, programming the project is simplicity itself. The motor is driven by lines 420 to 430 which are of course in a continous loop.

420    SYS K8055_SetDigitalChannel%,8
430     FOR J%=1 TO Sp%*Speed%:NEXT
440     SYS K8055_ClearDigitalChannel%,8

This sets Port 8 high, wastes some time and then sets the port low again. The SAA 1027 does all the rest. The length of time wasted determines the speed of rotation.

Change of direction is done by lines 300 and 310, which simply set output line either high or low.

300 IF Dir$="left" SYS K8055_SetDigitalChannel%,7
310 IF Dir$="right" SYS K8055_ClearDigitalChannel%,7

As usual, there is a zip file with the BASIC code and an executable file which allows you to use the program without installing BBC4W.

K8055_SAA1027_1_0.zip

10 REM K8055_SAA1027 20 REM Control one stepper motor with the Velleman K8055 interface board and a SAA1027 IC 30 REM Jochen Lueg 40 REM http://roevalley.com 50 REM Limavady, June 2012 60 REM Version 1.0 70 80 ON ERROR PROCerror 90 PROCK8055_init 100 PROCinit 110 ON CLOSE PROCclose 120 PROCwindow(680,300,"SAA 1027 driver") 130 OFF 140 SYS K8055_CloseDevice%,0 150 SYS K8055_OpenDevice%,0 160 170 PRINT 180 PRINT 190 PRINT " Left - Stop - Right . . . . . . Z X C" 200 PRINT " Fast - - - Slow . . . . . . 1 - 9" 210 PRINT 220 PRINT " Quit the progran . . . . . . Q" 230 240 REM Main loop 250 REPEAT 260 Key$=INKEY$(0):REPEAT UNTIL INKEY(0)=-1 270 IF Key$ = "z" OR Key$ = "Z" Dir$="left" :PROCreport 280 IF Key$ = "c" OR Key$ = "C" Dir$="right" :PROCreport 290 IF Key$ = "x" OR Key$ = "X" Dir$="not at all" : SYS K8055_ClearAllDigital%:PROCreport 300 IF Dir$="left" SYS K8055_SetDigitalChannel%,7 310 IF Dir$="right" SYS K8055_ClearDigitalChannel%,7 320 IF Key$="1" Speed%=10:PROCreport 330 IF Key$="2" Speed%=20 :PROCreport 340 IF Key$="3" Speed%=50 :PROCreport 350 IF Key$="4" Speed%=75 :PROCreport 360 IF Key$="5" Speed%=150 :PROCreport 370 IF Key$="6" Speed%=300 :PROCreport 380 IF Key$="7" Speed%=600 :PROCreport 390 IF Key$="8" Speed%=1000 :PROCreport 400 IF Key$="9" Speed%=1400 :PROCreport 410 IF Dir$<>"not at all" THEN 420 SYS K8055_SetDigitalChannel%,8 430 FOR J%=1 TO Sp%*Speed%:NEXT 440 SYS K8055_ClearDigitalChannel%,8 450 ENDIF 460 UNTIL Key$ = "q" OR Key$ = "Q" 470 PROCclose 480 END 490 500 510 520 DEFPROCclose 530 SYS K8055_ClearAllDigital% 540 SYS K8055_CloseDevice% 550 SYS "FreeLibrary",K8055_Board% 560 QUIT 570 ENDPROC 580 590 600 DEFPROCreport 610 LOCAL S% 620 S%=Speed% 630 IF Dir$="not at all" S%=0 640 PRINTTAB(1,11)"The motor is"; 650 IF Dir$="not at all" PRINT;" not turnig. "; 660 IF Dir$<>"not at all" PRINT;" turnig ";Dir$;" at speed ";S%;" " 670 ENDPROC 680 690 700 DEFPROCinit 710 Dir$="not at all" 720 Sp%=15000 730 Speed%=10 740 SYS K8055_WriteAllDigital%,0 750 ENDPROC 760 770 780 DEFPROCwindow(WindowWidth%,WindowHeight%,W$) 790 MODE 30 800 SYS "SetWindowPos",@hwnd%,0,0,0,WindowWidth%,WindowHeight%,6 810 SYS "SetWindowText",@hwnd%,W$ 820 VDU 26 830 COLOUR 15 840 *FONT Lucida Console,14,2 850 ENDPROC 860 870 880 DEFPROCerror 890 PRINT REPORT$;" at line ";ERL 900 SYS K8055_ClearAllDigital% 910 SYS K8055_ClearAllAnalog% 920 SYS K8055_CloseDevice% 930 SYS "FreeLibrary",K8055_Board% 940 END 950 ENDPROC 960 970 980 DEFPROCK8055_init 990 SYS"LoadLibrary","K8055D.dll" TO K8055_Board% 1000 SYS"GetProcAddress",K8055_Board%,"OpenDevice" TO K8055_OpenDevice% 1010 SYS"GetProcAddress",K8055_Board%,"CloseDevice" TO K8055_CloseDevice% 1020 SYS"GetProcAddress",K8055_Board%,"ReadAnalogChannel" TO K8055_ReadAnalogChannel% 1030 SYS"GetProcAddress",K8055_Board%,"ReadAllAnalog" TO K8055_ReadAllAnalog% 1040 SYS"GetProcAddress",K8055_Board%,"OutputAnalogChannel" TO K8055_OutputAnalogChannel% 1050 SYS"GetProcAddress",K8055_Board%,"OutputAllAnalog" TO K8055_OutputAllAnalog% 1060 SYS"GetProcAddress",K8055_Board%,"ClearAnalogChannel" TO K8055_ClearAnalogChannel% 1070 SYS"GetProcAddress",K8055_Board%,"ClearAllAnalog" TO K8055_ClearAllAnalog% 1080 SYS"GetProcAddress",K8055_Board%,"SetAnalogChannel" TO K8055_SetAnalogChannel% 1090 SYS"GetProcAddress",K8055_Board%,"SetAllAnalog" TO K8055_SetAllAnalog% 1100 SYS"GetProcAddress",K8055_Board%,"WriteAllDigital" TO K8055_WriteAllDigital% 1110 SYS"GetProcAddress",K8055_Board%,"ClearDigitalChannel" TO K8055_ClearDigitalChannel% 1120 SYS"GetProcAddress",K8055_Board%,"ClearAllDigital" TO K8055_ClearAllDigital% 1130 SYS"GetProcAddress",K8055_Board%,"SetDigitalChannel" TO K8055_SetDigitalChannel% 1140 SYS"GetProcAddress",K8055_Board%,"SetAllDigital" TO K8055_SetAllDigital% 1150 SYS"GetProcAddress",K8055_Board%,"ReadDigitalChannel" TO K8055_ReadDigitalChannel% 1160 SYS"GetProcAddress",K8055_Board%,"ReadAllDigital" TO K8055_ReadAllDigital% 1170 SYS"GetProcAddress",K8055_Board%,"ResetCounter" TO K8055_ResetCounter% 1180 SYS"GetProcAddress",K8055_Board%,"ReadCounter" TO K8055_ReadCounter% 1190 SYS"GetProcAddress",K8055_Board%,"SedtCounterDebouceTime" TO K8055_SetCounterDebounceTime% 1200 ENDPROC 1210

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