An AVR-Based Microstepping Bipolar Chopper Stepper Motor
- Open Source - The schematic, parts list, and
software are all freely downloadable!
- Hobbyist-friendly - No surface mount parts means allows
this drive to be easily repaired!
- DMOS driver chips rated at 55V and 3 Amps.
- Easy parts availability - Electronic parts are all
available at Digikey. Just add your own heat sink and mounting
- DIP Switch selectable modes of stepping:
- Full Step, Both Phases On
- Full Step, Wave Drive
- Half Step
- Quarter Step
- Sixth Step
- Eighth Step
- Tenth Step
- Twelfth Step
- Sixteenth Step (available on special request in place
of Twelfth Step mode with a special version of firmware)
- Optically isolated step, direction, & enable
These signals are ground referenced so no +5VDC is required - hook
directly to your parallel port.
- Selectable automatic idle current reduction to reduce motor
Motor current can be reduced if no steps are received for 3 seconds.
Oscilloscope Image, 202 kb
- DIP switch selectable motor test mode.
Allows for testing of motor/drive/wiring without an externally
generated step signal.
- Motor braking can be activated when drive is disabled.
Alternatively, motor braking can also be disabled such that the motor
will freewheel when drive is disabled.
- Motor current is adjustable by two potentiometers. (One for
each motor phase)
Fixed resistors may be substituted in place of the potentiometers for
cost savings or increased reliability.
- Removable screw terminals for all wiring connections.
- Status LED flashes during normal operation to let the user
know the microcontroller is running.
Illuminates solid during a fault condition.
- Quality double-sided printed circuit board with ground
plane and silkscreen legend.
Board size is 3.25" x 4.30" with mounting holes for #6 screws in each
Design & Configuration
- Motor connections (including motor voltage) are made on
the removable screw terminals on right side of the board.
- V+ is the Motor Power and must be externally fused.
(TP4) The driver chip can is rated up to +55 VDC, but allowance should
be made for back emf from the motor.
As such, I recommend a maximum of +45 VDC.
- V- is the Motor Power common (TP5)
- Motor Winding, B+
- Motor Winding, B-
- Motor Winding, A+
- Motor Winding, A-
- Logic power connections are also made on removable screw
terminals on the right side of the board.
- Vout is the +5 VDC output from the on-board LM7805
voltage regulator. (TP1)
- Vin is the +8-20 VDC input to the on-board voltage
regulator. At higher input voltages, the LM7805, heat sinking will be
- Com is the DC Common for the two previously mentioned
- Connections for the optically isolated signals are made on
the removable screw terminals on the bottom edge of the board.
- Opto Com is the DC Common for the optically isolated
signals. This is not connected to the the logic DC
- Direction - The motor will reverse directions when a
signal is applied. This signal must be set 2 us prior to the step
- Step - The motor will take a step on the rising edge
of a +5
VDC signal when it is applied to this terminal. Maximum step frequency
is 100 kHz. The Direction signal must be set for 2 us prior to the step
signal becoming active.
- Enable - The motor will be disabled unless a +5 VDC
signal is applied to this terminal.
If you do not have an enable signal and want your drive to always be
enabled... do not populate OP1 and where OP1 would have been installed,
short the pads corresponding to pins 4 and 5.
A photo of this modification can be found
here. (206 kb)
Please note that the motor shaft may 'jerk' when the drive is
enabled/disabled; exact position is not maintained.
Be sure to double and triple check all connections
before power is applied!!
This site contains all the information you need to build your own STMD.
If you'd like to purchase a tested product, kit, bare PCB, or other
components, details can be found here.
Last Updated: February 10th, 2013
Questions or Comments? (email)
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