A high I Stepper driver

This small project is designed to drive a stepper motor which needs a higher current than a single digital output of the Velleman board can supply. The ULN 2803 chip used by Velleman to drive the digital outputs has a factory rating of 0.5A per channel, though Velleman recommend a smaller current. The ports of the ULN 2803 can be switched in parallel, hence doubling the current that can be sunk. The small pcb shown below achieves this by connecting four pairs of outputs in parallel.

The motor shown is a 6V stepper motor which draws 1.2A per coil. By reducing the input voltage to 4.5V the circuit had no trouble driving this motor without causing an overload. But please take care - the ULN 2803 chip has a habit of quietly dying if it is asked to sink too much current.

The program

I have used the program to demonstrate the two driving modes of a unipolar stepping motor. Full step and half step. The full step method energizes the four coils in sequence, one at a time. Like this: A B C D A B C D A B C D and so on. Each pulse turns the motor by one step.

The half step method energizes first one coil, then the same coil plus the next in the series. This forces the rotor to a position half way between the two coils. The sequence looks like this: A AB B BC C CD D DA and so on.

The result is a much smoother action, though the speed is reduced by half.

Below is a link to a zip archive of the BBC BASIC for Windows program file and the executable of the same program, in case you don't have BB4W

K8055_high-I-stepper-files.zip

Here is a YouTube video of the project

Should you prefer using the K8061 interface board you may find the archive below quite useful:

K8061_high-I-stepper-files-1.zip

10 REM Single stepper motor driver 20 REM Version 1 30 REM For The Velleman K8055 USB interface # 40 REM Jochen Lueg 50 REM http://roevalley.com/newsbrowser/v-projects/v-index.htm 60 REM Limavady, January 2012 70 80 ON ERROR PRINT ERL;" ";REPORT$:END 90 PROCK8055_init 100 PROCinit 110 SYS K8055_CloseDevice% 120 SYS K8055_OpenDevice%,0 130 PRINT 140 PRINT " Motor controls" 150 PRINT 160 PRINT " Left . . . . . . Z" 170 PRINT " Right . . . . . . C" 180 PRINT " Stop . . . . . . X" 190 PRINT " Full step . . . . . . F" 200 PRINT " Half step . . . . . . H" 210 PRINT 220 PRINT 230 PRINT " Number keys above QWERTY Press for 1 second" 240 PRINT 250 PRINT " Fastest . . . . . . 1" 260 PRINT " Slowest . . . . . . 9" 270 PRINT 280 PRINT " Press 'S' to leave the program" 290 300 REPEAT 310 Key$=INKEY$(0) : REPEAT UNTIL INKEY(0)=-1 320 IF Key$="c" OR Key$="C" Direction$="Right" 330 IF Key$="z" OR Key$="Z" Direction$="Left" 340 IF Key$="s" OR Key$="S" Direction$="Finished" 350 IF Key$="x" OR Key$="X" Direction$="Stop" 360 IF Key$="h" OR Key$="H" Mode$="Half" 370 IF Key$="f" OR Key$="F" Mode$="Full" 380 IF Key$="1" T%=35S% :Speed$="Fast" 390 IF Key$="2" T%=70S% :Speed$="Fast-1" 400 IF Key$="3" T%=140S% :Speed$="Fast-2" 410 IF Key$="4" T%=280S% :Speed$="Fast-3" 420 IF Key$="5" T%=560S% :Speed$="Half" 430 IF Key$="6" T%=1120S% :Speed$="Slow+3" 440 IF Key$="7" T%=2240S% :Speed$="Slow+2" 450 IF Key$="8" T%=4480S% :Speed$="Slow+1" 460 IF Key$="9" T%=8960S% :Speed$="Slow" 470 IF Direction$="Right" AND Mode$="Full" THEN PROCfull_step_right 480 IF Direction$="Right" AND Mode$="Half" THEN PROChalf_step_right 490 IF Direction$="Left" AND Mode$="Full" THEN PROCfull_step_left 500 IF Direction$="Left" AND Mode$="Half" THEN PROChalf_step_left 510 IF Direction$ <> "Wait" PRINTTAB(1,16);Mode$;" step. Turning ";Direction$;" with speed ";Speed$;" " 520 IF Direction$="Stop" PRINTTAB(1,16)"Motor stopped " 530 IF Direction$="Stop" SYS K8055_ClearAllDigital%:Direction$="Wait" 540 UNTIL Direction$="Finished" 550 560 PRINTTAB(1,16)"All good things come to an end. " 570 SYS K8055_ClearAllDigital% 580 SYS K8055_CloseDevice% 590 QUIT 600 END 610 620 630 640 DEFPROChalf_step_right 650 FOR J%=1 TO 8 660 SYS K8055_WriteAllDigital%,HalfStep%(J%): FOR I%=1 TO T%:NEXT 670 NEXT 680 ENDPROC 690 700 `710 DEFPROChalf_step_left 720 FOR J%=8 TO 1 STEP -1 730 SYS K8055_WriteAllDigital%,HalfStep%(J%): FOR I%=1 TO T%:NEXT 740 NEXT 750 ENDPROC 760 770 780 DEFPROCfull_step_right 790 FOR J%=1 TO 4 800 SYS K8055_WriteAllDigital%,FullStep%(J%): FOR I%=1 TO T%:NEXT 810 NEXT 820 ENDPRO`

830 840 850 DEFPROCfull_step_left 860 FOR J%=4 TO 1 STEP -1 870 SYS K8055_WriteAllDigital%,FullStep%(J%): FOR I%=1 TO T%:NEXT 880 NEXT 890 ENDPROC 900 910 920 DEFPROCinit 930 COLOUR 128 940 CLS 950 COLOUR 15 960 W%=0 970 Direction$="Stop" 980 S%=5000 990 T%=S%*35 1000 Speed$="Fast" 1010 Mode$="Full" 1020 1030 DIM HalfStep%(8) 1040 HalfStep%(1)=&11 1050 HalfStep%(2)=&33 1060 HalfStep%(3)=&22 1070 HalfStep%(4)=&66 1080 HalfStep%(5)=&44 1090 HalfStep%(6)=&CC 1100 HalfStep%(7)=&88 1110 HalfStep%(8)=&99 1120 1130 DIM FullStep%(4) 1140 FullStep%(1)=%00010001 1150 FullStep%(2)=%00100010 1160 FullStep%(3)=%01000100 1170 FullStep%(4)=%10001000 1180 1190 ENDPROC 1200 1210 1220 DEFPROCK8055_init 1230 REM Typing errors in routine name do not generate an error message - they just hang up the program. 1240 REM These are all the system calls in the order found in the manual 1250 SYS"LoadLibrary","K8055D.dll" TO K8055_Board% 1260 SYS"GetProcAddress",K8055_Board%,"OpenDevice" TO K8055_OpenDevice% 1270 SYS"GetProcAddress",K8055_Board%,"CloseDevice" TO K8055_CloseDevice% 1280 SYS"GetProcAddress",K8055_Board%,"ReadAnalogChannel" TO K8055_ReadAnalogChannel% 1290 SYS"GetProcAddress",K8055_Board%,"ReadAllAnalog" TO K8055_ReadAllAnalog% 1300 SYS"GetProcAddress",K8055_Board%,"OutputAnalogChannel" TO K8055_OutputAnalogChannel% 1310 SYS"GetProcAddress",K8055_Board%,"OutputAllAnalog" TO K8055_OutputAllAnalog% 1320 SYS"GetProcAddress",K8055_Board%,"ClearAnalogChannel" TO K8055_ClearAnalogChannel% 1330 SYS"GetProcAddress",K8055_Board%,"ClearAllAnalog" TO K8055_ClearAllAnalog% 1340 SYS"GetProcAddress",K8055_Board%,"SetAnalogChannel" TO K8055_SetAnalogChannel% 1350 SYS"GetProcAddress",K8055_Board%,"SetAllAnalog" TO K8055_SetAllAnalog% 1360 SYS"GetProcAddress",K8055_Board%,"WriteAllDigital" TO K8055_WriteAllDigital% 1370 SYS"GetProcAddress",K8055_Board%,"ClearDigitalChannel" TO K8055_ClearDigitalChannel% 1380 SYS"GetProcAddress",K8055_Board%,"ClearAllDigital" TO K8055_ClearAllDigital% 1390 SYS"GetProcAddress",K8055_Board%,"SetDigitalChannel" TO K8055_SetDigitalChannel% 1400 SYS"GetProcAddress",K8055_Board%,"SetAllDigital" TO K8055_SetAllDigital% 1410 SYS"GetProcAddress",K8055_Board%,"ReadDigitalChannel" TO K8055_ReadDigitalChannel% 1420 SYS"GetProcAddress",K8055_Board%,"ReadAllDigital" TO K8055_ReadAllDigital% 1430 SYS"GetProcAddress",K8055_Board%,"ResetCounter" TO K8055_ResetCounter% 1440 SYS"GetProcAddress",K8055_Board%,"ReadCounter" TO K8055_ReadCounter% 1450 SYS"GetProcAddress",K8055_Board%,"SedtCounterDebouceTime" TO K8055_SetCounterDebounceTime% 1460 ENDPROC

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