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Step driver

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Il circuito per pilotare due motori passo-passo unipolari

On this circuit there are eight DC power switch you can open or close through PC parallel port: you can use it to drive two unipolar stepper motor or eight electric light bulb or DC motors.

Digital interface to PC uses optocouplers for safety reasons and you can connect up to six circuits to a single LPT, driving up to twelve step motors or 48 bulb: see iso-buffer for an in deep description.

You can find in this page a sample code for Windows based on VVIO project

Circuit components

Circuit power supply should be from 14 to 50V. Maximum single switch current is five ampere if you use IRF540 but circuit can handle 10 A maximum for all switch.  If you use logic level MOS, you can use power supply down to 7 V.

If your load is highly inductive, like motors, care should be used in diodes choice: they should be "fast recovery time" type and capable to sink load peak current. If you haven't any high speed diode, best to use slow 1N4001 then none.

C5 best choice is low ESR type but generic type should be right. Note you need high voltage type!

C1 22 uF - 63 Vl - Electrolytic
C2,C3 220 nF
C4 10 uF - Electrolytic or tantalum
C5 1000 uF - 63 Vl - Electrolytic
D1,D2,D3,D4,D5,D6,D7,D8 High speed diode (see text)
ISO1,ISO2,ISO3 6N135 - Optocoupler
JP1,JP2 5 poles connector, 5mm
JP3 5x2 poles connector, 5mm 2.54 mm
J1 2 poles connector, 5mm
Q1,Q2,Q3,Q4,Q5,Q6,Q7,Q8 IRF540 - Power MOS
R1,R3,R5 180 ohm
R2,R4,R6 4k7
R7 100 ohm 
R8 220 ohm
R9 1k8
U1 CD4094B - 8-bit shift register/latch
U2 LM317HV - Linear high voltage regulator

If power supply is under 30V, capacitor voltage should be lowered and you can use a "normal" LM317.


The pcb is a double layer but I have not used any plated holes; it is necessary to insert some small wire in order to connect the two sides of the printed circuit and, for some components, use the "double-layer soldering" technique.

In order to avoid difficulty soldering on top layer, best way is to use the following order:

If you see PCB top layer, you can't see a lot of connection... so you can do a single layer PCB and add some "flying" wire

Software, schematic and PCB will be found in unipolar.tgz file

licenza License
schematic.pdf Circuit schematic, in pdf format 
top.pdf Component pcb side, in pdf format
bottom.pdf Solder pcb side, in pdf format
assembly.pdf Components layout, in pdf format
LW_CVI Software for windows: LabWindows/CVI

To build this circuits you need:

If you need to drive a bipolar step motor, you can see Micro-step driver design.