described must be supplied with voltage in the range
8...24 VDC and the maximum output current is up to 2
A/channel (coil) with appropriate heat sink. Without
the heat sink, the controller can safely be used with
up to 250 mA per channel/coil. In addition, the
controller is equipped with a timer function (time is
continuously adjustable in the range of 0.5...70 s). The
START/STOP jumper configures the controller for
continuous or timed operation. Time is set using a
potentiometer and the countdown is triggered by
briefly short-circuiting the jumper pinsSTART/STOP.
Figure 1 shows the configuration of the controller
along with the most important elements of its design.
Schematic diagram of the circuit is shown in Figure 2.
Correct power supply is ensured by the 7805 stabiliser
together with capacitances C1-C4. Power stage is
implemented on the well-known L298 IC, which
incorporates two H-bridges. Its operation is
controlled by an ATtiny261 microcontroller, or more
precisely by a program in its memory. Micro-step
control is achieved by controlling the motor windings
with a PWM waveform. The PWM modulation
characteristics are triangular in shape. Such a solution
is uncomplicated and effective in most cases of motor
operation. Jumpers on the controller board are used
to configure the circuit. The jumper described as
HFRQ/L-FRQ is used to change the speed sub-band. If
fitted, a higher sequence frequency will be selected,
approximately 7...100 cycles per second (i.e., full
waveform periods per channel). The circuit operates
at a lower resolution of 1/8 step. Absence of a jumper
means a lower sequence frequency, i.e., approximately
1...10 cycles per second, and a higher microstep
resolution of 1/64. The STAT/DYN jumper determines
whether the motor will be de-energised during
standstill - static standstill (jumper on), or the power
supply will be maintained - dynamic standstill
(jumper off). At a static stop, almost free motor shaft
movement is possible, during dynamic stop, the
motor shaft is locked in its position, and here it must
be remembered that current flows through the coils,
which will cause the motor to heat up. This controller
has a timed operation function. It is switched on when
the START/STOP connector is short-circuited and lasts
for a time proportional to the position of
potentiometer PR1. Time is counted from the
moment the START/STOP jumper is removed. It is best
to replace the jumper with a reset-type monostable
button. If the jumper remains on, the controller will
operate at all times. A potentiometer attached to
screw connector X1 is used to adjust the direction and
speed - in the middle position the motor is stopped,
turning the potentiometer causes a gradual Increase
of its speed. Instead of this potentiometer, a
potentiometer joystick can be attached, in which case
the rotation of the motor will be proportional to the
direction and angle of the joystick.
Fig. 1.
STOP L-FRQDYN
US1
PR1
LED1
STAT H-FRQ
X1
START
X2 X3
US2
US3
STAT
H-FREQ
START
DYN
L-FREQ
STOP
SPEED AND DIRECTION
LR
2
