The 2008 Bipolar Stepper Motor Driver circuit has been replaced by a newer version.

2012 - Stepper Motor Driver Circuit

BIPOLAR Stepper Motor Driver (2008)

  This page features simple and inexpensive, stand alone BIPOLAR stepper motor driver using parts that are available from many sources.

  The driver is designed for medium and low speed applications with motors that draw up to 1.0 ampere per phase.

  This driver provides only basic control functions such as: Forward, Reverse, Stop and has a calculated Step rate adjustment range of 0.72 (1.39 sec) to 145 steps per second. (Slower and faster step rates are also possible. - See notes.)

  The only step angle for this driver is the design step angle of the motor itself. 'Half-stepping' is not possible.

  A 74194 - Bidirectional Universal Shift Register from the 74LS or 74HC - TTL families of logic devices to produce the stepping pattern.

Stepper Motor Driver PCB Circuit

  The following schematic is for the printed circuitboard version of the 2008 stepper motor driver.

Basic Controls For The Stepper Driver

  The direction is selected by an ON-OFF-ON toggle switch.

  The stepping rate is shown being set by a 1 Megohm potentiometer (RT). Using the component values shown for R1, RT, R2 and C1, the calculated step rate range is between 0.72 steps per second (1.39 seconds) to 145 steps per second.

Basic Stepper Motor Driver Operation
  1.   The LM555 (IC 1) astable oscillator produces CLOCK pulses that are fed to PIN 11 of the 74194 (IC 2) shift register.

  2.   Each time the output of the LM555 timer goes HIGH (positive) the HIGH state at the OUTPUT terminals of the 74194 (PIN's 12, 13, 14, 15) is shifted either UP or DOWN by one place.

      For the bipolar motor driver, two of the outputs are HIGH and two of the outputs are LOW at all times. The driver circuit produces four reversible combinations at the 'X' and 'Y' outputs:

    1 - 0 & 1 - 0,   0 - 1 & 1 - 0,   0 - 1 & 0 - 1 and 1 - 0 & 0 - 1

      Each clock pulse cause the sequences to shift one place to the right or left, depending on the direction control's setting.

  3.   The direction of the output shifting is controlled by switch S1. When S1 is in the OFF position (centre) the HIGH output state will remain at its last position and the motor will be stopped.

      Switch S1 controls the direction indirectly through transistors Q2 and Q3.

      When the base of Q2 is LOW the output shifting of IC 2 will be pins 15 - 14 - 13 - 12 - 15; .etc.

      When the base of Q3 is LOW the output shifting of IC 2 will be pins 12 - 13 - 14 - 15 - 12; .etc.

      The direction of the output's shifting determines the direction of the motor's rotation.

  4.   The four outputs of the 74194 are fed to one of the driver segments of a SN754410NE - H Bridge driver IC (IC 3).

      When an input of a SN754410NE segment is HIGH, its output will be HIGH.

      When an input of a SN754410NE segment is LOW, its output will be LOW.

  5.   The outputs of the SN754410NE are used in pairs that change their polarities on alternate clock pulses.

Inputs Vs. Outputs Waveforms

  The following diagram shows the stepping order for the outputs of the SN754410NE (IC 3) as compared to the input and output of the 74194 (IC 2). The output is shown stepping in one direction only.

  NOTE: In the diagram above, the order of the outputs of the 74194 does not correspond directly to the outputs of the SN754410NE. This is because two of the connections between these ICs are crossed on the circuitboard so that the circuitboards output terminals are arranged in an X1 - X2 - Y1 - Y2 order.

Integrated Circuit Chips Used

  It is not the purpose of this page to provide full explanations of how these devices work. Detailed explanations can be found through datatsheets that are available from many source on the internet.

74194 Stepper Motor Driver Notes

74194 Stepper Driver Initialization Notes

  The stepper motor driver is ready to start operation as soon as the the initialization delay is complete.

Please Read Before Ordering

  Due to delays in acquiring 74LS194 type ICs, the assembled circuitboards and kits will use the 74HC194 - CMOS type IC. The 74HC194 will be mounted in a socket to eliminate soldering this device during assembly.

  Although the 74HC194 is sensitive to damage from static discharge, once it is installed in its socket the IC is very safe as all of its pins are connected to the 5 volt supply or to common through low impedance paths.

  A good practice is to touch the work surface before touching the circuitboard.

PCB Parts Placement Diagram

Other Information And Diagrams
Step And Direction Controls

  The step and direction controls for the Bipolar motor driver are the same as those for the Unipolar motor driver. To avoid duplication, the diagrams from the Unipolar driver web page have been reused on the Bipolar driver page.

Single-Step Input

  The connections in the following diagram will allow the motor to make single steps. A toggle switch could be used to select between single and continuous steps if the 1 Megohm potentiometer was included in the circuit.

Stepper Driver Controlled By Computer Parallel Ports

  In most cases the 74194 stepper driver circuits can be directly controlled from the parallel ports of computers that have 0 and 5 volt output states.

  This also applies to other logic devices with 0 and 5 volt output states. Consult the particular device's datasheet for their specifications.

External Controls Using Transistors

External Controls Using Optoisolators

  The use of optoisolators provides complete isolation between the driver and the external control circuit.

Automated Motor Control Circuit - (Voltage Comparators)

  The circuit above replaces the direction control switch with a "window" type voltage comparator circuit. Potentiometer "R IN" could be a temperature or light sensing circuit.

  In a practical application the direction of the motors load, a heating duct damper for example, would bring the temperature represented by the voltage at R IN back to the range between the HIGH and LOW voltage setpoints.

  The limit switches at the outputs of the comparators are used to prevent the damper from going beyond its minimum and maximum positions by to stopping the motor.

  Also see Voltage Comparator Information And Circuits - Voltage Window Detector Circuit.

Slower Step Rates

  Additional capacitance can be added to the IC 1 circuit to provide slower motor step rates. There is a limit to this approach as control of the step rate becomes less accurate as the capacitance increases and at some point the timer will stop working due to the leakage currents of the capacitors.

Fast External Clock

  An external clock with a step rate greater than 145 steps per second can be connected to the driver circuit by removing capacitor C1. There is no limit on how slow the clock input can be.

Single Input Direction Control

  The following circuits allow the direction of the motor to be controlled by as single, ON-OFF input. The maximum input voltage is 5 Volts.

Disabling The L293's Outputs

  The L293 motor driver IC has outputs that can be disabled by connecting pins 1 and 9 to ground. Disabling the outputs will allow the motor to turn freely and can be used conserve power if the motor is not needed for a period of time.

  The SN754410NE's drivers are enabled in pairs, the 'Y' coil's drivers enabled via pin 1 and 'X' coil's drivers enabled via pin 9.

  When an enable input is high, the associated drivers are active and their outputs are in phase with their inputs. When the enable input is low, the associated drivers are inactive, their outputs are off and in a high-impedance or open-circuit state.

  When the drivers are disabled, only the power to the motor is turned off, the rest of the circuit remains active.

  The disable connections for IC 3 have not been brought out to a terminal block but provision has been made on the circuit board to allow connections directly to the board without having to drill new holes.

  To use the 'disable' inputs of the L293 , the section of copper trace between pins 1 and 16 of IC 3 must be cut and a jumper connected between pins 1 and 9. Pads have been provide have been provided on the circuitboard for the jumper.

  A wire is then connected to the board that is used to connect pins 1 and 9 to the circuits common through a switch, transistor or optoisolator. A pad is provided for this connection as well.

  The disable control can be a switch, transistor of optoisolator just the same as in the control circuits shown in the sections above.

  The following schematic shows how the basic circuit is modified to allow the outputs of the IC 3 to be disabled.

  The following diagram shows how the disable jumper between pins 1 and 9 of IC 3 and the lead to the disable switch (S2) are connected to the circuitboard. Also shown is the cut trace between pins 1 and 16 of IC 3.

Using Higher Current Motors

  The next circuit uses TIP125 and TIP126 Darlington type transistors to increase the current capacity of the 74194 driver circuit to 5 amps per winding.

  Depending on the current required for the motor, small heatsinks may be needed for the transistors.

Other Information

  Animated operation of stepper motors.

  The following links are for stepper motor related pages that have information on other types of driver circuits and motors.

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

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09 February, 2013