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Friday, 13 March 2009

Digital Speed Control

My design is based around three parts:

1. The controller board. This is a fully digital circuit that takes the 1ms to 2ms pulse from the receiver and converts it into a pwm train at 1Khz. It uses six cmos ics (74hc and 40 series) and a 4Mhz crystal clock. The only other components are one resistor and two capacitors to complete the crystal clock and a capacitor across the supply for smoothing. This was built on a printed board measuring 2 x 2.25 inches using standard components (on the boat there was no shortage of space). If surface mounted devices are used, the lot can be crammed into a much smaller space. The circuit can give a resolution of 128 steps (7bits). Some day I will expand it to have reverse function, but this is better done by a switcher circuit supplied from another channel (my reciever can give 7 channels and I am using only two at present).

2. The power board. This is the collection of mosfets and driver. It was built on a separate board so that I could experiment with different configurations and power densities, without touching the controller. My initial circuit used eight BUZ11 mosfets (4 each motor). The choice was because these transistors were easier to obtain. The circuit remains the same for transtors with higher current ratings.

3. A BEC circuit so that only the main battery is used. This is a switched mode power supply to supply the 5V to 6V needed by the receiver and servos, thereby eliminating the reciever battry. The circuit is based around the LM2576 and uses the minimum component count. This circuit can supply much larger current than ones based around linear devices, without getting hot, even on 14 cells.

Plans

Schematics and pulse diagrams in Adobe Acrobat (PDF) format

Schematics and pulse diagrams in PowerPoint 4 format

PCB layout in AutoTrax format

Temperature-controlled Fan

Circuit diagram:

Temperature-controlled Fan

Parts:

P1_____________22K   Linear Potentiometer (See Notes)

R1_____________15K @ 20°C n.t.c. Thermistor (See Notes)
R2____________100K 1/4W Resistor
R3,R6__________10K 1/4W Resistors
R4,R5__________22K 1/4W Resistors
R7____________100R 1/4W Resistor
R8____________470R 1/4W Resistor
R9_____________33K 4W Resistor

C1_____________10nF 63V Polyester Capacitor

D1________BZX79C18 18V 500mW Zener Diode
D2_________TIC106D 400V 5A SCR
D3-D6_______1N4007 1000V 1A Diodes

Q1,Q2________BC327 45V 800mA PNP Transistors
Q3___________BC337 45V 800mA NPN Transistor

SK1__________Female Mains socket

PL1__________Male Mains plug & cable

Device purpose:

This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain.

Circuit operation:

R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generate a fixed two-thirds-supply "reference" voltage, P1-R1 generate a temperature-sensitive "variable" voltage, and Q1 is used as a bridge balance detector.
P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.
This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.

Notes:

  • The circuit is designed for 230Vac operation. If your ac mains is rated at about 115V, you can change R9 value to 15K 2W. No other changes are required.
  • Circuit operation can be reversed, i.e. the fan increases its speed as temperature decreases, by simply transposing R1 and P1 positions. This mode of operation is useful in controlling a hot air flux, e.g. using heaters.
  • Thermistor value is not critical: I tried also 10K and 22K with good results.
  • In this circuit, if R1 and Q1 are not mounted in the same environment, the precise trigger points are subject to slight variation with changes in Q1 temperature, due to the temperature dependence of its Base-Emitter junction characteristics. This circuit is thus not suitable for use in precision applications, unless Q1 and R1 operate at equal temperatures.
  • The temperature / speed-increase ratio can be varied changing C1 value. The lower the C1 value the steeper the temperature / speed-increase ratio curve and vice-versa.
  • Warning! The circuit is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Wireless RF PWM dual motor controller

The transmitter circuit consists of WZ-X01 RF module, Holtek HT-640 encoder and 8-bit A/D converter. U1 ADC0804 converts the analog voltage to digital data; U2 encodes that data (D0~D6) along with D6, D7 and transmitting through the RF transmitter module. The potentiometer VR1 varies the voltage to the A/D U1 pin6, since only the lower 6 bits are used; the trim pot VR2 has to adjust so that the maximum input to the U1 will not exceed 1.25V. The S2 (D6) and S3 (D7) are used for controlling the rotation direction of the motors. S1 set the transmitter address; this address has to match with the address of the decoder circuit.


The receiver module WZ-R01 receives the data from the transmitter and feeds that data to the decoder U1 (HT-648L); the 8bit data will then be decoded. The first two significant bits D7 and D6 control the motor rotation direction. The lower 6 bits vary the duty cycle of the output pulse. U2 is a 12bit counter; it is configured so that it will reset itself every 64 counts. The oscillation circuit forms by U4c, U4d and U4e providing approximately 1MHz clock to the counter U2.

The 8-bit magnitude comparator U3 (74HCT688) compares the data from the counter U2 with the data of the decoder U1; when data from both are match, it will output a pulse to cause the D-flip flop U5 changing it's state.

By varying the data output of the decoder from 0-64, the duty cycle of the output pulse at U5 pin5 can also change from 0-100%. This output pulse will then be used to control the speed of the motor.

With 1MHz clock input the PWM frequency output is about 15.6KHz. The motor has less audible noise when run at a frequency higher than 10KHz.You may need to change the frequency depending on the motor you're going to use.

The motor driver section is very straightforward; the LMD18200 can handle 3A continuous motor current and 6A peak. In this circuit the sign/magnitude mode of operation is implemented. The current sensing circuit provides protection to both the driver and the motor; it set at 2A max. You can change the current limit by using a different current sensing resistor value (see LMD18200 data sheet for details) or the voltage reference at pin6 of the U7Op-Amp

The above picture is the prototype, It works great! We had been able to control the motors at more than 100 feet away.

You may download this whole page in MS word format.

Three Phase Voltage Regulator - SFR

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Photographs

Wednesday, 11 March 2009

Fast Acting Electronic Circuit Breakers

Fast Acting Electronic Circuit Breakers

The circuit breakers on this page make use of the Zetex - ZXCT1009 "High Side Current Monitor' integrated circuit. The circuits have variable trip current settings and are designed for low current applications.

Zetex - ZXCT1009 "High Side Current Monitor'

The current sensing IC is placed in the supply side of the circuit ahead of the isolation device. This allows the common line of the circuit to remain free of voltage dropping resistances.

For information on the operation of the ZXCT1009 current monitor itself, please refer to the manufacturers data sheet at - ZETEX - ZXCT1009 Data Sheet (PDF)


Two circuit breaker designs are shown; The first has its power isolation device on the Low or common side of the circuit while the second has it isolation device on the High or supply side of the circuit. Both designs use MOSFET devices to isolate the suppiy from the load.

The overload detection and trip system is completely electronic and therefore has a very fast response time (1/120th of a second or less for a full wave DC supply). This allows the load to be disconnected almost instantaneously when an over current condition is detected.



- Low Side Isolation Circuit Breaker -

This circuit has its isolation device, Q1, on the Low or common side of the circuit. The disadvantage of this method is that the breaker cannot easily be used in typical circuit configurations that share a low side or negative common.

The method is simple to implement however and a wide range of output devices are available. The transistor used to test this circuit was a IRL520 MOSFET


Low Side Circuit Breaker

Circuit Controls and Indicators

  • S1 resets the circuit after and overload trip has occurred.

  • ROUT - ADJ adjusts the tripping current level.

  • LED - D2 will turn OFF when an overload has occurred and the circuit has tripped.





- High Side Isolation Circuit Breaker -

This circuit has its isolation device, IC 3, on the High or Supply side of the circuit. This allows the circuit breaker to be more easily used in typical circuit configurations that share a low side or negative common.

IC 3 is a PROFET® BTS409L1 - 'Smart High Side power Switch' from INFINEON.


High Side Circuit Breaker

Circuit Controls and Indicators

  • S1 resets the circuit after and overload trip has occurred.

  • ROUT - ADJ adjusts the tripping current level.

  • LED - D2 will turn OFF when an overload has occurred and the circuit has tripped.

LED - D3 is optional and is connected to the internal diagnostics system of the BTS409L1 and will turn ON to indicate various fault conditions. These are listed in the BTS409L1 data sheet.



Very - Basic Operation Of Both Circuit Breakers

  1. As the current through RSENSE increases the voltage across resistors ROUT - MAX and ROUT - ADJ increases proportionally.

  2. When the voltage at the MINUS input of IC 2A rises above the voltage at the PLUS input its OUTPUT will go LOW.

  3. When the OUTPUT of IC 2A goes LOW it causes the Flip-Flop formed IC 2B to change states, producing a LOW condition at it's OUTPUT.

  4. Depending on the circuit used, a LOW at the output of IC 2B causes the Gate of Q1 or the Input Terminal of IC 3 to go LOW. This will cause Q1 or IC 3 to turn OFF and open the circuit.



Circuit Breaker Page Notes

  • The maximum Input to Output voltage of the ZXCT1009 is 20 Volts. There are ways to increase this voltage but these are not shown on this page.

  • With the component values shown the calculated adjustable trip current range is between 0.23 and 3 amps.

  • A heat sink may be required for transistor Q1 or IC 3 at higher current levels.

  • Capacitor C3 provides a short delay time so that the circuit automatically resets itself when power is applied.

  • Capacitor C4 prevents the circuit's protection from being disabled if S1 is held closed. This means that when S1 is held closed the circuit will reset and then will quickly trip again if an overload is present. If C4 is not used the circuit breaker cannot trip as long as S1 is held closed. This may be desirable in certain situations and might be considered as an option.

  • Both Q1 and IC 3 have internal diodes to protect them from being reversed biased. This could happen if the power transformer's fuse failed while the breaker was connected to a circuit with a large filter capacitor. In this case reverse current would be shunted around the isolation devices and into the circuit breaker's power supply until the circuit had been discharged.

  • Diode D1 and capacitor C1 provide a short term sub-power supply for the control circuitry in case there is a drop in the voltage of the main supplies voltage during a dead short at the output of the breaker.

  • For more information on voltage comparators please refer to this page; Voltage Comparator Information And Circuits.

  • There are other devices from Zetex and other manufactures that could also be used in this type of circuit.

  • The ZXCT1009 used has a SOT-23 surface mount style case that is quite small. To aid in using this device a "PROTO-BOARD ADAPTER FOR SOT-23-5" listed as DigiKey part number 33205CA-ND. is recommended. (The distance between the pins is 0.100in or 2.54mm.)

PROTO-BOARD ADAPTER FOR SOT-23



BIPOLAR Stepper Motor Driver (74194)

BIPOLAR

Stepper Motor Driver (74194)

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 0.6 amperes 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.

A printed circuitboard is available for this circuit.


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 L293D - H Bridge driver IC (IC 3).

    When an input of a L293D segment is HIGH, its output will be HIGH.

    When an input of a L293D segment is LOW, its output will be LOW.

  5. The outputs of the L293D 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 L293D (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 L293D. 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

  • IC 1 - LM555 Timer - Normally configured as an astable oscillator but can be used a monostable timer for 1 step at a time operation or can be used as a buffer between external inputs and IC 2. (See later Diagrams.)

  • IC 2 - 74194 - 4-Bit Bidirectional Universal Shift Register. The shift register provides the logic that controls the direction of the drivers output steps.

    This circuit can use either the 74LS194 or the 74HC194 shift register IC. Their logic functions are identical but the 74HC194 IC is a CMOS type that can be damaged by static electricity discharges. Antistatic precautions should be used when handling the 74HC194 to avoid damage.

    If you are purchasing your own parts use the 74LS194 IC if it is available.

  • IC 3 - L293D - Quad - Half H bridge, motor driver IC. Each segment can handle currents of up to 600 milliamps and voltages up to 36 volts. In this circuit 2 output segments are used for each motor phase to form a full H bridge for each coil of the motor.

  • IC 4 - LM7805 - Positive 5 Volt Regulator. Provides low voltage power to the driving circuitry and can also power external control circuits.

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

  • Due to the lack of error detection and limited step power, this circuit should not be used for applications that require accurate positioning. (The driver is designed for hobby and learning uses.)

  • There are links to other stepper motor related web pages further down the page. These may be helpful in understanding stepper motor operation and control.

  • For the parts values shown on the schematic, if the external potentiometer (RT) is set to "ZERO" ohms, the calculated CLOCK frequency will be approximately 145 Hz and a motor will make 145 steps per second. This step rate should be slow enough for most motors to operate properly.

    The maximum RPM at which stepper motors will operate properly is low when compared to other motor types and the torque the motor produces drops rapidly as its speed increases. Testing may be needed to determine the minimum values for RT and C1 to produce the maximum CLOCK frequency for any given motor. Data sheets, if available, will also help determine this frequency.

  • If RT is set to 1 Megohm, the calculated step rate will be 0.73 Hz and the motor would make 1 step every 1.39 seconds.

    There is no minimum step speed at which stepper motors cannot operate. Therefore, in theory, the values for RT and C1 can be as large as desired but there are practical limitations to these values. The main limitation is the 'leakage' current of electrolytic capacitors.

  • External CLOCK pulses can also be used to control the driver by passing them through IC 1 via the "T2" terminal of the circuitboard. Using IC 1 as an input buffer should eliminate "noise" that could cause the 74194's output to go into a state where more than one output is HIGH.

  • If stepping rates greater than 145 per second are needed, capacitor C1 can be replaced with one of lower value.

    A 0.47uF capacitor would give a calculated range of 1.5 to 310 steps per second.

    A 0.33uF capacitor would give a calculated range of 2.2 to 441 steps per second.

    Alternately, capacitor C1 can be removed from the circuitboard and an external clock source connected at terminal 'T2'. With C1 removed, the practical limit on the step rate is the motor itself.

  • In the above items the "calculated" minimum and maximum CLOCK frequencies are valid for the nominal part values shown. Given the tolerances of actual components and the leakage currents of electrolytic capacitors the actual CLOCK rates may be lower or higher.

  • The direction of the motor can 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 Q2 and Q3 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 Q2 and Q3 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 pins 15 and 14 will go to a HIGH state.

    Making the bases of both Q2 and Q3 LOW at the same time can be used to reset the SN74194 to its starting position without having to remove the circuit power.

  • The outputs of the L293 driver (IC 3) can be disabled if desired. For more information; see the section further down this page.

  • Each stepper motor will have its own power requirements and as there is a great variety of motors available. This page cannot 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 up to 600 milliamps per phase, depending on the particular motor.

    Motors that operate at voltages lower than 12 volts can also be used with this driver but a separate supply of of 9 to 12 volts will be needed for the control portion of the circuit in addition to the low voltage supply for the motor.

  • A LED connected to the output of the LM555 timer (IC 1) flashes at the CLOCK frequency. If a direction has been selected, The motor will move one step every time the led turns ON.

  • There is no CLOCK output terminal on the circuitboard but there is a pad to the right of the LED that can be used if a clock output signal is required. This pad is connected to pin 3 of the LM555 IC.

  • The LM7805, positive 5 volt regulator used on the circuitboard can also be used to provide power for external control circuits. The regulator can easily dissipate up to 1 watt.

    For a 12 volt supply, external circuits can draw up to 100 milliamps.

    For a 24 volt supply, external circuits can draw up to 25 milliamps.

  • The photo of the circuitboard shows the tab of the 7805 regulator cut off, this is an option that is available on request.


74194 Stepper Driver Initialization Notes

  • When power is applied to the 74194 Stepper Driver circuit there is a very short delay before stepping of the outputs can begin. The delay is controlled by Capacitor C2, resistor R4 and transistor Q1.

  • The function of the delay is to allow the outputs of IC 2 to be set with pins 12 and 13 in a HIGH state and pins 14 and 15 in a LOW state before direction control becomes active. The delay also prevents IC 1 from oscillating until IC 2 has been set.

  • If the power to the circuit is turned off, there should be a pause of at least 10 seconds before it is reapplied. The pause is to allow capacitor C2 to discharge through R4 and D2.

  • If the initialization delay were not used, IC 3 could have: none, any or all of its outputs in a high state when stepping is started. This would cause the motor to move incorrectly or not at all during normal operation.

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


Stepper Circuit Board Parts List

Qty. Part # DigiKey Part # Description
1 - IC 1 - LM555CNFS-ND - 555 TIMER SINGLE 0-70DEG C 8-DIP
1 - IC 2* - 296-9183-5-ND - 74194 - BI-DIR SHIFT REGISTER 16-DIP
1 - IC 3 - 296-9518-5-ND - L293D - QUAD HALF-H DRVR 16-DIP
1 - IC 4 - LM7805ACT-ND - 7805 REG POS 1A 5V +/-2% TOL TO-220
- - -
3 - Q1, 2, 3 - 2N3904FS-ND - 2N3904 - NPN SS GP 200MA TO-92
1 - D1 - 160-1712-ND - LED 3MM GREEN DIFFUSED
1 - D2 - 1N4148FS-ND - DIODE SGL JUNC 100V 4.0NS DO-35
1 - D3 - 1N4001FSCT-ND - DIODE GEN PURPOSE 50V 1A DO41
- - -
4 - R1, 2, 8, 9 - 3.3KQBK-ND - RES 3.3K OHM 1/4W 5% CARBON FILM
3 - R4, 6, 7 - 10KQBK-ND - RES 10K OHM 1/4W 5% CARBON FILM
1 - R3, 5 - 470QBK-ND - RES 470 OHM 1/4W 5% CARBON FILM
- - -
1 - C1 - P5174-ND - CAP 1.0UF 50V ALUM LYTIC RADIAL
2 - C2, 3 - P5177-ND - CAP 4.7UF 50V ALUM LYTIC RADIAL
1 - C4 - P5168-ND - CAP 470UF 35V ALUM LYTIC RADIAL
- - -
4 - - ED1602-ND - TERMINAL BLOCK 5MM VERT 3POS










Circuitboards And Parts

The following picture is of an assembled circuitboard for the Bipolar Stepper Motor Driver. The board measures 2 inches by 3.8 inches and has been commercially made. The board is not tinned or silkscreened.

The relative positions of the terminal blocks at the sides and ends of the circuitboard correspond with those in the schematic diagram and the control circuit examples.

The photo of the circuitboard shows the tab of the 7805 regulator cut off, this is an option that is available on request.

The price for 1 circuitboard is 10.50 dollars US plus postage.

The price for 1 kit of parts and a circuit board is 21.00 dollars US plus postage.

The price for 1 Assembled circuitboard is 24.00 dollars US plus postage.

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

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.

When handling the board, avoid nonconductive surfaces such as plastics or glass. If the circuit board is to be placed in a plastic case, do the assembly work on a wood or metal surface that is connected to earth. Also avoid carpeted areas during assembly.

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.


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.

  • 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 R1 and 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 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 L293D'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.



Other Information

Animated operation of stepper motors.

http://de.nanotec.com/schrittmotor_animation.html


The following links are for stepper motor related pages that have 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


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.

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03 February, 09

UNIPOLAR Stepper Motor Driver (74194)

UNIPOLAR

Stepper Motor Driver (74194)

This page features simple and inexpensive, stand alone UNIPOLAR 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 amperes 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.

The stepper motor driver on this page replaces the Unipolar Stepper Motor Driver (74194) 2007 That was previously available through this web site.

A printed circuit board is available for this circuit.


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 74194's OUTPUT terminals, (PIN's 12, 13, 14, 15), is shifted either UP or DOWN by one place.

    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.

  3. The outputs of the 74194 are fed to four sets of paralleled segments of a ULN2803 Darlington driver (IC 3).

    When an input of a ULN2803 segment is HIGH, its darlington transistor will turn ON and that OUTPUT will conduct current through one of the motors coils.

  4. As the coils of the motor are turned ON in sequence the motor's armature rotates to follow these changes. Refer to following diagram.


Inputs Vs. Outputs Waveforms

The following diagram shows the stepping order for the outputs of the ULN2803 (IC 3) as compared to the input and output of the 74194 (IC 2). The output is shown stepping in one direction only.


Integrated Circuit Chips Used

  • IC 1 - LM555 - Timer, normally configured as an astable oscillator but can be used a monostable timer for 1 step at a time operation or can be used as a buffer between external inputs and IC2. (See later Diagrams.)

  • IC 2 - 74194 - 4-Bit Bidirectional Universal Shift Register. The shift register provides the logic that controls the direction of the drivers output steps.

    This circuit can use either the 74LS194 or the 74HC194 shift register IC. Their logic functions are identical but the 74HC194 IC is a CMOS type that can be damaged by static electricity discharges. Antistatic precautions should be used when handling the 74HC194 to avoid damage.

    If you are purchasing your own parts use the 74LS194 IC if it is available.

  • IC 3 - ULN2803 - 8 Segment, Darlington, High Current, High Voltage Peripheral Driver. Each segment can handle currents of up to 500 milliamps and voltages up to 50 volts. In this circuit 2 output segments are connected in parallel, this allows a maximum output current of 1 amp per phase.

  • IC 4 - LM7805 - Positive 5 Volt Regulator. Provides low voltage power to the driving circuitry and can also power external control circuits.

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

  • Due to the lack of error detection and limited step power, this circuit should not be used for applications that require accurate positioning. (The driver is designed for hobby and learning uses.)

  • There are links to other stepper motor related web pages further down the page. These may be helpful in understanding stepper motor operation and control.

  • For the parts values shown on the schematic, if the external potentiometer (RT) is set to "ZERO" ohms, the calculated CLOCK frequency will be approximately 145 Hz and a motor will make 145 steps per second. This step rate should be slow enough for most motors to operate properly.

    The maximum RPM at which stepper motors will operate properly is low when compared to other motor types and the torque the motor produces drops rapidly as its speed increases. Testing may be needed to determine the minimum values for RT and C1 to produce the maximum CLOCK frequency for any given motor. Data sheets, if available, will also help determine this frequency.

  • If RT is set to 1 Megohm, the calculated step rate will be 0.73 Hz and the motor would make 1 step every 1.39 seconds.

    There is no minimum step speed at which stepper motors cannot operate. Therefore, in theory, the values for RT and C1 can be as large as desired but there are practical limitations to these values. The main limitation is the 'leakage' current of electrolytic capacitors.

  • External CLOCK pulses can also be used to control the driver by passing them through IC 1 via the "T2" terminal of the circuitboard. Using IC 1 as an input buffer should eliminate "noise" that could cause the 74194's output to go into a state where more than one output is HIGH.

  • If stepping rates greater than 145 per second are needed, capacitor C1 can be replaced with one of lower value.

    A 0.47uF capacitor would give a calculated range of 1.5 to 310 steps per second.

    A 0.33uF capacitor would give a calculated range of 2.2 to 441 steps per second.

    Alternately, capacitor C1 can be removed from the circuitboard and an external clock source connected at terminal 'T2'. With C1 removed, the practical limit on the step rate is the motor itself.

  • In the above items the "calculated" minimum and maximum CLOCK frequencies are valid for the nominal part values shown. Given the tolerances of actual components and the leakage currents of electrolytic capacitors the actual CLOCK rates may be lower or higher.

  • The direction of the motor can 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 Q2 and Q3 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 Q2 and Q3 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 pins 15 and 14 will go to a HIGH state.

    Making the bases of both Q2 and Q3 LOW at the same time can be used to reset the SN74194 to its starting position without having to remove the circuit power.

  • Each stepper motor will have its own power requirements and as there is a great variety of motors available. This page cannot 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 up to 1,000 milliamps depending on the particular motor.

    Motors that operate at voltages lower than 12 volts can also be used with this driver but a separate supply of of 9 to 12 volts will be needed for the control portion of the circuit in addition to the low voltage supply for the motor.

  • A LED connected to the output of the LM555 timer (IC 1) flashes at the CLOCK frequency. If a direction has been selected, The motor will move one step every time the led turns ON.

  • There is no CLOCK output terminal on the circuitboard but there is a pad to the right of the LED that can be used if a clock output signal is required. This pad is connected to pin 3 of the LM555 IC.

  • The LM7805, positive 5 volt regulator used on the circuitboard can also be used to provide power for external control circuits. With its tab trimmed off, the regulator can easily dissipate up to 1 watt.

    For a 12 volt supply, external circuits can draw up to 100 milliamps.

    For a 24 volt supply, external circuits can draw up to 25 milliamps.

  • The photo of the circuitboard shows the tab of the 7805 regulator cut off, this is an option that is available on request.


74194 Stepper Driver Initialization Notes

  • When power is applied to the 74194 Stepper Driver circuit there is a very short delay before stepping of the outputs can begin. The delay is controlled by Capacitor C2, resistor R4 and transistor Q1.

  • The function of the delay is to allow the outputs of IC 2 to be set with pin 12 in a HIGH state and pins 13, 14 and 15 in a LOW state before direction control becomes active. The delay also prevents IC 1 from oscillating until IC 2 has been set.

  • If the power to the circuit is turned off, there should be a pause of at least 10 seconds before it is reapplied. The pause is to allow capacitor C2 to discharge through R4 and D2.

  • If the initialization delay were not used, IC 3 could have: none, any or all of its outputs in a high state when stepping is started. This would cause the motor to move incorrectly or not at all during normal operation.

The 2008 version of the stepper motor driver is ready to start operation as soon as the the initialization delay is complete.


Stepper Circuit Board Parts List

Qty. Part # DigiKey Part # DigiKey Description
1 - IC 1 - LM555CNFS-ND - IC TIMER SINGLE 0-70DEG C 8-DIP
1 - IC 2* - 296-9183-5-ND - IC BI-DIR SHIFT REGISTER 16-DIP
1 - IC 3 - 497-2356-5-ND - IC ARRAY EIGHT DARLINGTON 18 DIP
1 - IC 4 - LM7805ACT-ND - IC REG POS 1A 5V +/-2% TOL TO-220
- - -
3 - Q1, 2, 3 - 2N3904FS-ND - IC TRANS NPN SS GP 200MA TO-92
1 - D1 - 160-1712-ND - LED 3MM GREEN DIFFUSED
1 - D2 - 1N4148FS-ND - DIODE SGL JUNC 100V 4.0NS DO-35
1 - D3 - 1N4001FSCT-ND - DIODE GEN PURPOSE 50V 1A DO41
- - -
4 - R1, 2, 8, 9 - 3.3KQBK-ND - RES 3.3K OHM 1/4W 5% CARBON FILM
3 - R4, 6, 7 - 10KQBK-ND - RES 10K OHM 1/4W 5% CARBON FILM
1 - R3, 5 - 470QBK-ND - RES 470 OHM 1/4W 5% CARBON FILM
- - -
1 - C1 - P5174-ND - CAP 1.0UF 50V ALUM LYTIC RADIAL
2 - C2, 3 - P5177-ND - CAP 4.7UF 50V ALUM LYTIC RADIAL
1 - C4 - P5168-ND - CAP 470UF 35V ALUM LYTIC RADIAL
- - -
4 - - ED1602-ND - TERMINAL BLOCK 5MM VERT 3POS







* - The DigiKey part number for IC 2 is for the 74HC194 - CMOS IC. This IC is a CMOS type that can be damaged by static electricity discharge.

DigiKey does not carry the 74LS194 in small quantities. It is available for other sources such as Mouser Electronics - stock number 47053 and Jameco Electronics - stock number 59574LS194AN as well as many other sources. Be sure that the IC's have the DIP package.

* - The Part Number for Q1, Q2 and Q3 is for 2N3904s. Almost any NPN, Switching or Small signal type will work, the 2N4400 is one example.




Circuitboards And Parts

The following picture is of an assembled circuitboard for the Unipolar Stepper Motor Driver. The board measures 2 inches by 3 inches and has been commercially made. The board is not tinned or silkscreened.

The relative positions of the terminal blocks at the sides and ends of the circuitboard correspond with those in the schematic diagram and the control circuit examples.

The photo of the circuitboard shows the tab of the 7805 regulator cut off, this is an option that is available on request.

The price for 1 circuitboard is 9.50 dollars US plus postage.

The price for 1 kit of parts and a circuit board is 19.00 dollars US plus postage.

The price for 1 Assembled circuitboard is 22.00 dollars US plus postage.

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

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.

When handling the board, avoid nonconductive surfaces such as plastics or glass. If the circuit board is to be placed in a plastic case, do the assembly work on a wood or metal surface that is connected to earth. Also avoid carpeted areas during assembly.

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


PCB Parts Placement Diagram




Other Information And Diagrams


Wiring for longer distances.

If the motor is some distance from the circuit board or power supply, 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 connected using larger gauge wire.

This will keep most effects of the motors current pulses away from the supply to the circuit board. A filter capacitor could be placed in the motor's supply circuit as well.


Connecting A 6 Lead Motor to the Stepper Driver

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


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.


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.

  • 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 R1 and 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 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.


Using Low Voltage Motors

Stepper motors that require less than 12 volts can be controlled by the driver by removing diode D3 from the circuitboard and connecting a external power supply to the control section of the driver.

Also, IC 4 could be removed from the circuitboard and a regulated 5 volt supply connected at the '+5V' terminal.


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.


Using Higher Current Motors

The next circuit uses TIP125 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.

http://de.nanotec.com/schrittmotor_animation.html

For the motor driver circuit on this web 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 that have 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




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.


Laser Pointer - Across and Along The Track Detection.

Laser Pointer - Across and Along The Track Detection.


This train detector makes use of hand held laser pointer devices that are widely available to detect trains over long distances.

WARNING Laser Pointers must be used with great caution as they may cause eye damage. Follow the directions that are supplied with these devices carefully or permanent injury could result.


The following diagram shows the basic laser pointer circuit. It is identical to the infrared circuit except that the infrared LED's have been replaced by the laser pointer unit.

Due to the long range of these devices this detector method can easily span great distances and could be used to detect trains in a long section of straight track such as in a lader yard or across the throat of a very wide yard.

Very Long Range Laser Pointer Detector


Determining the value of R1 for laser pointer diodes.

Laser pointers are not designed for this type of application and careful selection of R1 is required. testing should be carried out to determine the best resistance value for a particular pointer.

It is best to start with a high resistance for R1, 500 ohms for example, and decrease it in steps until the pointer will produce enough light energy to saturate the detector.

If you can see the light hitting the phototransistor this should be more than enough for the circuit. The pointer used for testing this detector needed about 38 milliamps for it to give off enough light to be easily seen by the naked eye.

Not enough current and the pointer will not 'lase'. - Too much current and the diode can be damaged.


Wiring The Pointer For Testing

Laser pointers are not designed to be taken apart, so for testing purposes the following method might be used to connect an external supply to the laser diode without damaging the pointer itself.

In this way if the detector is not to your liking you still have a functional laser pointer and not an expensive junk box oddity.

  • Use a mini test lead clip such as Radio Shack part number 270-372B to reach inside the body of the pointer and connect to the spring terminal.

  • If the laser pointers body is made of metal a small alligator clip can be used to connect to the body where the end cap screws into the body.

  • To hold the switch closed, clamp the pointer in its mount so that the button is depressed or hold the switch closed with a small wire tie.

  • Be careful to determine the correct polarity of the terminals or the laser diode could be ruined.

  • The leads from the clips can then be connected, through R1, to the power source.


The next diagram shows a possible mounting that could be used for testing a laser pointer detector.

Laser Pointer Mounting Method


Emitter/Detector Alignment

Aligning the emitter and detector should be straight forward as the the light can be seen hitting the detector. For best results the height of the beam should be at coupler height.


For information on Voltage Comparators please see the Voltage Comparator Information page at this site.


LM339 Data sheet - National Semiconductor (.pdf)

LM393 Data sheet - National Semiconductor (.pdf)

Pinout Diagram For Various Devices.



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.


Stall Motor Switch Machine Circuits

Stall Motor Switch Machine Circuits

Multiple Location Control of Stall Motor Switch Machines


Alternate Location Control of Stall Motor Switch Machines


Full And Half wave DC power supplies and other control options for Stall-Motor switch machines.

Full Wave DC - Stall Motor Switch Machine Power Supply


Half Wave DC - Stall Motor Switch Machine Power Supply


Very Simple SPDT of Stall Motor Switch Machines

The next schematic shows three methods of controlling Stall Motor Switch Machines with an SPDT toggle switch and two resistors. This method wastes most of the current.

SPDT Control of Stall Motor Switch Machines


Push Button Control of Stall Motor Switch Machines

The next schematic shows three methods of controlling Stall Motor Switch Machines with momentary contact push button switches.

These circuits might be of use if slow motion type switch motors were to be installed on a layout that already had push buttons mounted on the control panels. This would then allow a transistion to the new switch machines with out having to change the control panel's buttons.

Push Button Control of Stall Motor Switch Machines

In circuits 1 and 2 the buttons must be held closed until the turnout throw arm of the switch machine has stopped moving.

Circuit 3 will keep power supplied to the motor for a few seconds after the push button has been released, allowing the turnout to finish its throw.




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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