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74194 Unipolar Stepper Motor Driver

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					74194 Unipolar Stepper Motor Driver                                                              http://home.cogeco.ca/~rpaisley4/Stepper.html




                          Unipolar Stepper Motor Driver (74194)




                                      A printed circuit board is available for this circuit.

                 This page features a simple and reasonably inexpensive unipolar stepper motor driver that can be used
                to drive low power, slow speed stepper motor applications.

                 The circuit is based on the SN74LS194 - Bidirectional Universal Shift Register. The circuit is
                designed to drive UNIPOLAR type stepper motors and provides only basic control functions -
                Forward, Reverse, Stop and Speed adjustment up to 100 steps per minute.

                 The only step angle for this driver is the design step angle of the motor itself.

                 The driver is not complex and is cheaper than many dedicated driver/controller devices and the parts
                are reasonably easy to find.

                 For the purposes of this page the direction control function is selected by an ON-OFF-ON type toggle
                switch. This could be easily replaced by another method such as transistors controlled by a PC's
                parallel output port.

                 Speed control is by means of a potentiometer but the circuit could accept pulses or controls from other
                sources such as a push button or a simple computer interface. The direction could also be controlled by
                a computer interface.

                NOTE: - Due to the lack of error detection or correction and limited step power, this circuit
                should not be used for applications that require accurate control or positioning accuracy. The
                driver is intended for hobby and learning uses only.


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74194 Unipolar Stepper Motor Driver                                                             http://home.cogeco.ca/~rpaisley4/Stepper.html



                 This web page uses integrated circuits from the SN74LS- family of TTL devices. It is not the purpose
                of this page to provide detailed explanations of how these devices work and an understanding of simple
                logic circuits would be helpful to the user.

                 Do not be discouraged by this however as the circuit's operation is quite simple.


                                        Basic Stepper Motor Driver Circuit
                 The following diagram is for the main circuit of the motor driver.

                 A testing version is shown later on this page. The testing circuit is laid out differently and shows the
                SN7474 in logic block form and LED's are used to indicate the motor coils being switched.




                                                  Stepper Motor Driver circuit

                 The blue line on the drawing is the path that the CLOCK pulses of the drive circuit follow.


                                      Basic Stepper Motor Driver Operation
                   1. The 555 astable oscillator produces a series of CLOCK pulses that are fed to PIN 11 of the
                      SN74194 integrated circuit.



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74194 Unipolar Stepper Motor Driver                                                             http://home.cogeco.ca/~rpaisley4/Stepper.html


                   2. Each time the CLOCK pulse goes HIGH (positive) the HIGH state at the SN74194's OUTPUT
                      terminals, (PIN's 12, 13, 14, 15), is shifted either UP or DOWN y one place. Refer to the
                      "Stepper Motor Driver Waveforms" diagram.

                        The direction of this shifting is controlled by switch S2. When S2 is in the center OFF position
                       the HIGH output state will remain in its last position and the motor will be stopped.

                        When the base of Q6 is LOW the shifting will be PIN 12 - 15 - 14 - 13 - 12 .etc.

                        When the base of Q7 is LOW the shifting will be PIN 12 - 13 - 14 - 15 - 12 .etc.

                        The direction of the pulse shifting determines the direction of motor rotation.

                   3. The pulses from the OUTPUT's of the SN74194 are fed to four segments of the ULN2003
                      Driver. When the input of a segment is HIGH, its darlington transistor will turn ON and its
                      OUTPUT will conduct current through one of the motors coils.

                   4. As the coils of the motor are turned ON in sequence the motor rotates to follow these steps.
                      Refer to following diagrams.


                                            Integrated Circuit Chips Used
                        The SN74LS194 - 4-Bit Bidirectional Universal Shift Register.

                        The SN74LS74 - Dual 'D' Type Positive-Edge-Triggered Flip-Flops with Preset and Clear.

                        The ULN2003 - 7 Segment, Darlington, High Current, High Voltage Peripheral Driver. Its
                       outputs can handle currents of up to 500 milliamps and voltages up to 50 volts.

                         The LM555 - Timer, normally configured as an astable oscillator but can be used a monostable
                       timer for 1 step at a time operation. (See later Diagrams.)

                NOTE: The 7400 series logic devices are largely considered to be obsolete. They are easy to use
                however and fairly inexpensive. For this reason they were chosen for this circuit over more
                sophisticated devices. Also, they provide the user with greater learning opportunities as various
                sections of the circuit can be tested on a breadboard before building the full driver circuit.


                 The following diagram shows the stepping order of the inputs to ULN2003 Peripheral Driver for
                forward and reverse motor directions. Pin numbers are not indicated as this depends on the PCB layout.

                 Each positive pulse at the SN74194's - OUTPUT terminals turns ON one of the stepper motor's coils.




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74194 Unipolar Stepper Motor Driver                                                             http://home.cogeco.ca/~rpaisley4/Stepper.html




                                            ULN2003 Motor Driver Stepping Order


                                         74194 Stepper Motor Driver Notes
                        There are some links to other stepper motor related web pages further down the page. These
                       may be helpful in understanding stepper motor operation and control.

                        With the parts values shown on the schematic and capacitor C1 being 1uF. If resistor R1 is set
                       to "ZERO" ohms the calculated CLOCK frequency will be approximately 100Hz and the motor
                       will make 100 steps per second. This CLOCK frequency will be slow enough for most motors to
                       operate properly.

                         The maximum RPM at which stepper motors will operate properly is quite low and the torque
                       the motor can produce drops of rapidly as motor speed increases. Testing may be needed to
                       determine the minimum values for R1 and C1 to produce the maximum CLOCK INPUT
                       frequency for any given motor. Data sheets, if available, will also help determine this frequency.

                        Some motors can handle higher CLOCK input frequencies. This depends largely on the
                       construction of the motor itself.

                        If R1 had a maximum resistance of 1 Megohm the calculated CLOCK frequency would be 1Hz
                       and the motor would make 1 step per second.

                        There is no minimum step speed at which stepper motors cannot operate. Therefore, in theory,
                       the values for R1 and C1 can be as large as desired. There are practical limitations to these values
                       though and the 555 timer data sheet should be consulted for more information.

                        Provision has been made on the printed circuit board to change the values of R1 and C1 through
                       external connections. It will also be possible to inject CLOCK pulses through these connections
                       for external step control.




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74194 Unipolar Stepper Motor Driver                                                             http://home.cogeco.ca/~rpaisley4/Stepper.html


                        In the above items the "calculated" minimum and maximum CLOCK frequencies are valid for
                       the actual parts values shown. Given the tolerances of real components and the leakage currents
                       of electrolytic capacitors the actual CLOCK rate could be lower or higher.

                        The Switch S1 is an option that could be used to stop the motor if desired. Closing S1 will stop
                       the 555 oscillator thereby stopping the CLOCK input pulses.

                        The switch was connected across the timing capacitor as this did not produce output noise
                       problems and was easier to externally connect to the circuit.

                        S1 could be replaced by an NPN transistor for electronic control of the CLOCK.

                        The CLOCK input pulses could be supplied from other sources but any "Noise" on the CLOCK
                       input could throw the SN74194 into a bad state. For this reason the pulses must be clean.

                        It would be best to pass any external input pulses through the 555 timer chip first. This
                       possibility has been provided for on the printed circuit board.

                        The SN7474 does not have a control function but is used to provide a sub routine when power is
                       applied to the circuit. This allows the SN74194 to "SET" its output states to PIN 15 - HIGH and
                       PINs 12, 13 and 14 - LOW before the DIRECTION control switching transistors, Q6 and Q7,
                       become active.

                         The First CLOCK pulse occurs when power is applied to the circuit (the OUTPUT of the 555
                       timer will go HIGH). DIRECTION control becomes active on the Second CLOCK input pulse. If
                       a direction is selected the motor will step on the Third CLOCK pulse.

                        The motor may step forward, backward or not at all on the second CLOCK pulse. This is part of
                       the output setting process.

                        Direction control is active when the OUTPUT at PIN 8 of the SN7474 has a HIGH state.

                        Logically speaking the SN7474 method used to initialize the circuit may not be the best but at
                       the relatively low frequencies use in this circuit, about 100Hz, it seems to work just fine. Without
                       this sub routine the SN74194 could have all, any or none of its outputs in a HIGH state after
                       power is applied to the circuit.

                        The 3.3K ohm resistor and the 4.7uF capacitor connected to the SET terminals, PINS 4 and 10,
                       of the SN7474 - FLIP-FLOP's ensures that the outputs at pins 6 and 8 go to a LOW state when
                       power is applied to the circuit.

                        When power is applied to the circuit it is possible that none, one or all of the outputs that
                       control the motor (Q1-5) could be ON for the first CLOCK cycle. For this reason the power
                       supply must be able to handle four times the rated motor current. If the motor step rate is very
                       slow this extra current draw may be lengthy.

                        The Direction of the motor could be controlled by another circuit or the parallel output port of a
                       PC. This will work as long as the voltage at the bases of Q6 and Q7 can be made lower than 0.7
                       volts. Additional NPN transistors may be required to achieve this result, depending on the
                       method used.

                        If the bases of both Q6 and Q7 are made LOW at the same time the SN74194 will go into a
                       RESET mode. This will cause the step sequence to stop and on the next clock pulse PIN 15 will
                       go to a HIGH state.

                        Making the bases of both Q6 and Q7 LOW at the same time can be used to reset the SN74194
                       to its proper starting position without having to remove the circuit power.


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74194 Unipolar Stepper Motor Driver                                                              http://home.cogeco.ca/~rpaisley4/Stepper.html


                        The controls and step generator portions of the motor driver circuit require a 5 volt regulated
                       power supply. This supply is shown on the schematic and is included on the printed circuit board.

                        The stepper motor will have its own power requirements and as there is a great variety of
                       motors available this page cannot hope to give information in this area. Users of this circuit will
                       have to determine motor phasing and power requirements for themselves.

                        Power for the motors can be regulated or filtered and may range from 12 to 24 volts with
                       currents of between 150 and 500 milliamps depending on the particular motor.

                        As shown on the schematic the CLOCK frequency has an output via Q5. There is no specific
                       purpose for this but because of the way the printed circuit board is layed out it was very easy to
                       provide this output. The clock output is not TTL compatible but is an open collector darlington
                       that can sink up to 500 milliamps.

                        This OUTPUT could be used if there was a need to drive two or more motors at the same
                       CLOCK speed. Another use could be as an feed back to a counter circuit if a specific number of
                       steps were desired.

                        A LED is connected to the output of the CLOCK that flashes at the CLOCK frequency. One
                       step of the motor for every time the led turns ON if a direction has been selected.


                                               Stepper Motor Driver Test Circuit




                                      Stepper Motor Driver circuit initial testing version.



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74194 Unipolar Stepper Motor Driver                                                            http://home.cogeco.ca/~rpaisley4/Stepper.html


                 This schematic shows the SN7474 in logic block form with its two "D" type FLIP-FLOP's. This
                circuit was used to test the stepper motor driver circuits operation.

                 Section FF1 acts as a binary divider while FF2 acts as a RS FLIP FLOP. After one division step the
                FLIP FLOP is SET to Q-high.

                 This allows the SN74194 to "SET" its output states to PIN 15 - HIGH and PINs 12, 13 and 14 - LOW
                before the DIRECTION control switching transistors, Q6 and Q7, become active.

                 Switch S1 allows the clock to be stopped or pulsed for single step control.

                 The POWER (14), COMMON (7) and CLEAR (CLR) (1,13) connections of the SN7474 are not
                shown on the schematic diagram to make the drawing less cluttered. The CLEAR terminals are
                connected to the +5 volt supply.


                 The next diagram shows the basic waveforms for the stepper motor driver circuit.




                                              Stepper Motor Driver Waveforms

                 The next diagram shows a simplified function diagram of the 74194 if it were built from 7474 - 'D'
                type Flip-Flops.




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74194 Unipolar Stepper Motor Driver                                                           http://home.cogeco.ca/~rpaisley4/Stepper.html




                                               Stepper Motor Driver Equivalent



                 The following picture is of a printed circuit board for the Stepper Motor Driver. The terminal block
                positions correspond with those on the schematic shown below.




                                            Stepper Motor Driver - Circuit Board

                 To reduce the overall height of the circuit the mounting tab has been trimmed from the 7805 regulator.


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74194 Unipolar Stepper Motor Driver                                                          http://home.cogeco.ca/~rpaisley4/Stepper.html


                (A TO-220 cased regulator was used as a TO-92 case would be too small for a 24 volt power supply.)
                With the tab trimmed off of the regulator it can easily handle 1 watt.




                                                    Regulator Tab Trimmed

                 The price for 1 circuit board is 11.00 dollars US plus postage.

                 The price for 1 kit of parts and a circuit board is 25.00 dollars US plus postage.

                 The price for 1 Assembled circuit board is 28.00 dollars US plus postage.

                 If you are interested in a circuit board and parts for this circuit please send a message to the
                following email address: rpaisley4@cogeco.ca


                                               Circuit Board Schematic
                 The following diagram shows the printed circuit board's Stepper Motor Driver circuit with the circuit
                boards basic external connection terminals. The motor coils have been omitted from this diagram but
                the external speed control potentiometer and direction switch have been included.




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74194 Unipolar Stepper Motor Driver                                              http://home.cogeco.ca/~rpaisley4/Stepper.html




                                      Stepper Motor Driver - Circuit Board Connections




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74194 Unipolar Stepper Motor Driver                                               http://home.cogeco.ca/~rpaisley4/Stepper.html




                                  Stepper Motor Driver - Circuit Board Parts Placement

                                        Stepper Circuit Board Parts List
                 Qty   -         CIRCUIT PART         -      MOUSER PART #   -                      MOUSER DE
                  1    -   74LS194                    -   526-NTE74LS194A    -   Replacement Digital ICs 4BIT B
                  1    -   74LS74                     -   595-SN74LS74ANE4   -   Dual Pos-Edge-Trig D-Type Flip
                  1    -   ULN2003AN                  -   595-ULN2003AN      -   Peripheral Drivers and Actuators
                  1    -   NE555N                     -   511-NE555N         -   Timers General Purp Single
                  1    -   L7805ACV                   -   511-L7805ACV       -   Voltage Regulators 5.0V 1.0A Po
                  2    -   2N3904                     -   512-2N3904D81Z     -   Small Signal Transistors NPN Tr


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74194 Unipolar Stepper Motor Driver                                                            http://home.cogeco.ca/~rpaisley4/Stepper.html



                  1    -   512-1N4001                       -   512-1N4001                 - Rectifiers Vr/50V Io/1A T/R
                  1    -   470uF/35V                        -   140-XRL35V470-RC           - Radial Electrolytic Capacitors 35
                  1    -   10uF/25V                         -   140-XRL25V10-RC            - Radial Electrolytic Capacitors 35
                  1    -   4.7uF/25V                        -   140-XRL25V4.7-RC           - Radial Electrolytic Capacitors 35
                  1    -   1uF/25V                          -   140-XRL25V1.0-RC           - Radial Electrolytic Capacitors 35
                  1    -   GREEN 3mm LED                    -   859-LTL-4231               - Standard LED Green Diffused
                  3    -   10K 1/4W                         -   291-10K-RC                 - 1/4W 5% Carbon Film Resistors
                  2    -   3.3K 1/4W                        -   291-3.3K-RC                - 1/4W 5% Carbon Film Resistors
                  1    -   470 OHM 1/4W                     -   291-470-RC                 - 1/4W 5% Carbon Film Resistors
                  2    -   2 POS. TERMINAL BLOCK            -   651-1729018                - PCB Terminal Blocks 2P 5mm 9
                  3    -   3 POS. TERMINAL BLOCK            -   651-1729021                - PCB Terminal Blocks 3P 5mm 9




                                        Other Information And Diagrams
                 The motor drive current capacity of the stepper driver circuit could be increased by placing a second
                ULN2003 IC on top of the first and then soldering their leads together. (I have not tried this but is
                should work fine if a only few hundred milliamps are needed.)


                                                  Wiring for longer distances.

                                                                   <

                 If the motor is some distance from the circuit board or powersupply, it might be best to separate the
                motor's power supply lead from the circuit board's supply as illustrated in the next diagram. The motor
                could be supplied with larger gauge wire as well.

                 This will keep most effects of the motors current pulses away from the supply to the circuit board.




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74194 Unipolar Stepper Motor Driver                                              http://home.cogeco.ca/~rpaisley4/Stepper.html




                                      Connecting A 6 Lead Motor to the Stepper Driver




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74194 Unipolar Stepper Motor Driver                                                          http://home.cogeco.ca/~rpaisley4/Stepper.html




                 It may be necessary to move the coil leads around to get the motor to turn properly. Leave one wire
                connected permenantly and change the other three coil leads as needed.


                                        Single-Step Configuration Of The Driver #1

                 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..




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74194 Unipolar Stepper Motor Driver                                                            http://home.cogeco.ca/~rpaisley4/Stepper.html




                 NOTE - In the above single-step mode the motor will not move correctly for the first two closes of the
                step switch after the power is applied to the circuit. This is because the 7474 IC will have disabled the
                direction control until the 74194 has set its outputs to the starting configuration.


                                        Single-Step Configuration Of The Driver #2

                 Another single step control method would be to replace the direction control switch with two
                pushbutton switches and operate the clock oscillator at a realtively slow rate.




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74194 Unipolar Stepper Motor Driver                                         http://home.cogeco.ca/~rpaisley4/Stepper.html




                                      External Controls Using Transistors




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74194 Unipolar Stepper Motor Driver                                                           http://home.cogeco.ca/~rpaisley4/Stepper.html


                                           External Controls Using Optoisolators




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


                                       Automated Motor Control Circuit - (Voltage)




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74194 Unipolar Stepper Motor Driver                                                           http://home.cogeco.ca/~rpaisley4/Stepper.html




                 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.

                        When the voltage at the centre tap of R IN is between the HIGH and LOW voltages set by
                       resistors R1, R2, and R3 the motor will be stopped.

                        When the voltage at the centre tap of R IN is above the HIGH voltage between R1and R2 the
                       motor will be step in the FWD direction.

                        When the voltage at the centre tap of R IN is below the LOW voltage between R2 and R3 the
                       motor will be step in the REV direction.

                 In a practical application the motion 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 would be used to stop the motor to prevent the
                damper from going beyond its minimum and maximum positions.

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



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74194 Unipolar Stepper Motor Driver                                                             http://home.cogeco.ca/~rpaisley4/Stepper.html




                                                         Slower Step Rates

                  Additional capacitance can be added to the 555 timer 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 leakage currents of the capacitors.




                                                         Other Information

                 Animated operation of unipolar stepper motors.

                http://nanotec.de/page_static__schrittmotor_animation__en.html

                 For the motor driver circuit on this wep page only 1 coil is ON at a time so the rotor of the motor
                would be aligned with one of the stator's poles and not half way between poles as shown in the
                animation.


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

                www.cs.uiowa.edu/~jones/step/circuits.html

                www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html


                The motors used to test this circuit were:
                  1.
                       JAPAN SERVO CO. (From an old floppy drive)
                       TYPE KP4M4-001
                       75 OHM / PHASE
                       0.15 AMP / PHASE




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74194 Unipolar Stepper Motor Driver                                                       http://home.cogeco.ca/~rpaisley4/Stepper.html


                   2. AIRPAX : LA82720-M1 (From a chart drive)
                       24 VOLT
                       60 OHMS / COIL
                       7.5 DEGREES / STEP



                Return to the Main Page



                                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.

                Return to the Main Page

                25 February, 2008




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