his project allows you to
control the speed, direction, and step size of a
unipolar four-phase stepper motor. The controller
is capable of handling
motor winding currents of up to 1.25
amps per phase and it operates from a
single supply voltage of 6-30 volts DC.
A unique feature of this project is
that thecircuit can operate in either
remote mode or stand-alone mode. In
the stand-alone mode, an on-board
pulse generator and a four-position DIP
switch allows you to demonstrate all of
the functions without any additional
connections. This mode is perfect for
demonstrating basic stepper motor
greater than the voltage rating of the
motor for improved performance.
Stable voltage for the restof the
circuit is obtained by regulating the
input voltage down to 5V with U4, a
LM78L05 voltage regulator IC.
Capacitors C7, C1, and C5 provide
additional voltage filtering. U1 is capable of supplying up to 100 mA of current.
The heart of the stepper controller
is U1, a UCN5804B stepper-motor
translator/driver IC. It contains a
CMOS logic section for the sequencing
logic and ahigh-voltage bipolar output
section to directly drive a unipolar stepper motor. U1 can generate waveforms
for three different sequence modes: (1)
If you’re interested in robotics, motion control,
or just want to learn about stepper motors, then
you should try building this versatile stepper
Pin Assignments GND
Pin Assignments -
control principles. The circuit even
has LEDs that show the energized
phases for each step.
In remote mode, all motor functions can be interfaced to external
logic or a microcontroller. This
allows the controller to be incorporated
into a robot, an X-Y plotter, or any
motion control project you have in
Referto the schematic of the stepper driver shown in Figure 1. Power is
supplied by a DC wall transformer or
DC power supply at P1.
The voltage can be anything from
6 to 30 volts, depending upon the rating of the stepper motor. The stepper
motor uses most of the current in this
circuit, so it is powered directly from
the transformer output through resistors R1 & R2.
These resistors limit thecurrent to
the motor and allow the motor to be
operated with a power supply voltage
TRANSLATOR/DRIVERFULL-STEP with two phases energized, (2) FULL-STEP WAVE and (3)
HALF-STEP. The waveforms for
these three sequence modes are
shown in Figure 5.
Diodes D1-4 are clamps to prevent damage to U1 if the outputs
swing below ground when driving the
inductive load of the motor.
Each of the LEDs L1-4 light
when the corresponding output goes
LOW and are useful for observing
the output waveforms. ResistorR3
provides current limiting to the
Pins 9, 10, 14, and 15 of U1
are control inputs for phase, halfstep, direction, and output-enable.
These signals are pulled-down to a
logic LOW level by resistors R7-11.
The control signals go to both
Resistors (Except where noted, resistors are 5%, 1/4 Watt)
R1,2 ....... 50 Ohm, 5 Watt
R3 ........ 330 Ohm (Orange, Orange, Brown, Gold)
R4........ 10 K Ohm (Brown, Black, Orange, Gold)
R5 ........ 22 K Ohm (Red, Red, Orange, Gold)
R6 ........ 220 K Ohm (Red, Red, Yellow, Gold)
R7-12 ..... 100 K Ohm (Brown, Black, Yellow, Gold)
R13 ....... 100 K Ohm Potentiometer
C1-3 ......... 0.1 uF, Ceramic, marked: 
C4-6 .......... 1.0 uF, 16V Tantalum or Electrolytic
C7 ........... 470 uF, 35V Electrolytic