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Circuits Designed by Dave Johnson, P.E.

60hz Clock Generator is Line PoweredThis circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit.  The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit . . . Hobby Circuit designed by David A. Johnson P.E.-February, 1999

Circuit Protects from Battery Polarity ReversalThis simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was. . . Circuit by David Johnson P.E.-March, 2002

CMOS Schmitt Trigger IC Makes VCOBy changing the supply voltage fed to a classic 4584 Schmitt trigger type oscillator, the oscillator frequency can be changed over a range of 50:1.  A 74HCU04 inverter is used at the output of the 4584 to maintain a constant TTL logic level signal. . . Circuit by David Johnson P.E.-December, 2002

Line Powered 60hz Clock GeneratorThis circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit.  The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit. . . Circuit by David Johnson P.E.-February, 1999

Protects from Battery Polarity ReversalThis simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was . . . Hobby Circuit designed by David A. Johnson P.E.-March, 2002




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60hz Clock Generator is Line Powered -  This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit.  The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit . . . Hobby Circuit designed by David A. Johnson P.E.-February, 1999

A for mains synchronization has two separate outputs for each half-period -  EDN-Design Ideas 03/22/2013    Generate independent short pulses at positive- and negative-going AC mains zero crossings.__ Circuit Design by Dusan Ponikvar

A Sine/Square Wave Oscillator for Your Workbench -  It uses a switched capacitor filter IC to give a very good envelope stability.___ SiliconChip

Adaptive Schmitt trigger tames unruly signals -  08/12/13  EDN-Design Ideas Some biomedical, sensor, and other signals can be almost impossible to derive a clean trigger from.  This circuit could help.  In biomedical instrumentation   (for example), we're sometimes faced with very noisy or badly-behaved signals from which we need to derive information.  In this example, I needed to "square up" a respiration signal, which can exhibit wide variations in amplitude and frequency, along with a wandering baseline.  Presented here is an adaptive "super-Schmitt, " with many adjustable parameters, that did an extremely good job of taming the input signal.  __ Circuit Design by Michael Dunn

Add a Schmitt-trigger function to CPLDs, FPGAs & applications -  10/13/05 EDN-Design Ideas For slow-slewing signals, hysteresis solves trigger problem__ Circuit Design by Stephan Roche, Santa Rosa, CA

AMI-to-NRZI-Direct-Conversion Tolerates Unequalized Pulse Tails -  03/06/08  EDN-Design Ideas Using a simple ECL Schmitt trigger, you can convert three-level AMI signals to NRZI.   AMI   (alternate-mark inversion) is a three-levelópositive, zero, negativeócopper-cable transmission code with the useful property of having no dc component for ease of ac coupling using capacitors or line-coupling transformers and a spectral peak at one-half the symbol rate.  The zeros symbols transmit as 0V; the ones symbols transmit at half-unit intervals with alternating-line polarity to maintain the dc balance.__ Circuit Design by Glen Chenier

Changes Improve Schmitt Trigger -  05/13/99 EDN-Design Ideas The classical Schmitt trigger circuit that youíll find in textbooks provIdeas some noise immunity, such as for the front end of magnetic pickup in position-sensor circuits(Figure 1a].  You adjust the two threshold levelsePDF contains many circuits, scroll to find this one.   __ Circuit Design by Ron Patrick

Circuit Protects from Battery Polarity Reversal -  This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was. . . Circuit by David Johnson P.E.-March, 2002

Circuit Yields Accurate Absolute Values -  07/05/01  EDN-Design Ideas The circuit in Figure 1 delivers the absolute value of the input signal with an accuracy better than 10 ppm of the full-scale range.  The circuit has low zero-crossing error.  You can use it as an asynchronous demodulator, as a source__ Circuit Design by Marco Pisani, Istituto di Metrologia G Colonnetti, Turin, Italy

CMOS Schmitt Trigger IC Makes VCO -  By changing the supply voltage fed to a classic 4584 Schmitt trigger type oscillator, the oscillator frequency can be changed over a range of 50:1.  A 74HCU04 inverter is used at the output of the 4584 to maintain a constant TTL logic level signal. . . Circuit by David Johnson P.E.-December, 2002

Configurable logic gates' Schmitt inputs make versatile Monostables -  05/25/06  EDN-Design Ideas You can assemble a pulse-generation circuit from a simple Schmitt-input AND gate plus a resistor-capacitor timing network.  However, if you need a logic function thatís not a standard catalog item, you need a Schmitt-input gate or __ Circuit Design by Glenn Chenier, Allen, TX

Contact-debouncing algorithm emulates Schmitt trigger -  7-Jul-05 EDN-Design Ideas Another approach to solving the ubiquitous contact debounce problem__ Circuit Design by Elio Mazzocca, Technical Consultant, Adelaide, South Australia

DPP adds versatility to VFC -  14-Nov-02 EDN-Design Ideas The basic VFC(voltage-to-frequency converter] in Figure 1 comprises an integrator(IC1] and a Schmitt-trigger circuit(IC2].  The integrator converts the dc input voltage, VIN , to a linear voltage ramp, and the Schmitt trigger sets the limits of the integrator's output voltage.  Feedback around both circuits provIdeas the condition for oscillation__ Circuit Design by Chuck Wojslaw, Catalyst Semiconductor, Sunnyvale, CA

Greatly improve dV/dt immunity of SCRs -  12/09/13  EDN-Design Ideas Improve dV/dt immunity of SCRs by three orders of magnitudeThe SCR is a switching semiconductor device, whose theoretical basics were published by Moll et al.  in 19561.  __ Circuit Design by Marian Stofka

Line Powered 60hz Clock Generator -  This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit.  The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit. . . Circuit by David Johnson P.E.-February, 1999

Low-Component-Count Zero-Crossing Detector is Low Power -  03/14/13  EDN-Design Ideas A simple opto-coupled circuit produces a logic level output signal synchronized to the power line.  There are many circuits published showing zero-crossing detectors for use with 50- and 60-Hz power lines.  Though the circuit variations are plentiful, many have shortcomings.  This Design Idea shows a circuit that uses only a few commonly available parts and provIdeas good performance with low power consumption.  In the circuit shown in Figure 1, a waveform is produced at VO with rising edges that are synchronized with the zero crossings of the line voltage, VAC.  The circuit can be easily modified so that it produces a falling-edge waveform that is synchronized with VAC.  __ Circuit Design by Carlos Castro-Miguens

Mains Synchronization Has Two Separate Outputs for Each Half-Period -  03/22/13  EDN-Design Ideas Generate independent short pulses at positive- and negative-going AC mains zero crossings.  Often a measurement of weak signals has to be performed in the presence of strong interference from the ac power mains.  If the interfering signal cannot be filtered out, then you can still obtain a clean result by making two consecutive measurements separated in time by an odd number of half-periods of the mains and calculating the average of the two measurements.  The interfering signals have opposite polarities in consecutive measurements, and averaging cancels them out.  If you average several consecutive pairs of measurements, the results will improve still further.  __ Circuit Design by Dusan Ponikvar

Mains-Driven Zero-Crossing Detector Uses Only a Few High-Voltage Parts -  12/01/11  EDN-Design Ideas You can get isolation with low power consumption using this simple circuit.  The circuit in this Design Idea generates a zero-crossing pulse off the ac mains and provIdeas galvanic isolation.  The falling edge of the output pulse happens at approximately 200 μsec before the zero crossing.  You can use the circuit to safely stop the triggering of a thyristor gate, giving it time to properly turn off.  The circuit generates short pulses only when the mains voltage is approximately 0V, thereby dissipating only 200 mW at 230V and a 50-Hz input.__ Circuit Design by Luca Matteini, Agliana, Italy

MOS transistors form current-mode Schmitt trigger -  12/03/98 EDN-Design Ideas Schmitt triggers are useful in both analog and digital circuits for reducing sensitivity to noise and disturbances.  Current-mode Schmitt triggers are particularly useful in photodetectors, bar-code readers, and optical remote controls.  The resistorless current-mode SchmittSchmitt triggers are useful in both analog and digital circuits for reducing sensitivity to noise and disturbances.  Current-mode Schmitt triggers are particularly useful in photodetectors, bar-code readers, and optical remote controls.  The resistorless current-mode Schmitt.   File has several circuits, scroll to this one__ Circuit Design by Tai-Shan Liao, Chun-Ming Chang, and Wen-Yaw Chung, Chung-Yuan, Christian University, Taiwan, China

Oscillator extends Schmitt triggers' reach -  EDN-Design Ideas 01/19/95    Fig 1a shows input filters and Schmitt triggers wired to square up tachometer signals.  However, given normal var-iations in IC lots and operating environments, Fig 1a's fixed-bias scheme (comprising RV and RG) stands little chance of holding the dc level at the Schmitt triggers' inputs anywhere near halfway between their thresholds.  Because the strength of tachometer signals is proportional to speed, below a certain speed, this circuit does not respond properly to the resulting low-level signals.   __ Circuit Design by Phil Harvey, Technology Integration Inc, Bedford, MA

Paralleling Decreases autozero-amplifier noise by a factor of two -  06/07/07  EDN-Design Ideas By simply paralleling four amplifiers of a quad auto-zero amplifier, you can decrease output noise by a factor of two__ Circuit Design by MariŠn ätofka, Slovak University of Technology, Bratislava, Slovakia

Protects from Battery Polarity Reversal -  This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was . . . Hobby Circuit designed by David A. Johnson P.E.-March, 2002

Resistor network extends Schmitt trigger's reach -  09/13/01 EDN-Design Ideas The circuit in Figure 1 shows a familiar technique for converting a low-level analog signal to digital form.  Resistors R1 and R2 set the quiescent dc level at the Schmitt inverter's input to a value roughly equal to the midpoint of the hysteresis band.  Capacitor C1 removes dc content from VIN, such that the Schmitt trigger's input signal, VI, centers itself on the midhysteresis level__ Circuit Design by Anthony Smith, Scitech, Biddenham, UK

Sample/ Hold Has Zero Droop & Infinite Hold -  App Note/ 12 / Jul-08___ Maxim Integrated

Sample-And-Hold Amplifier Holds the Difference Of Two Inputs -  07/24/08  EDN-Design Ideas You can fulfill a requirement for sampling the difference of two signals in two classic ways.  You can subtract the two input signals with an instrumentation amplifier whose output connects to an input of a classic sample-and-hold amplifier .   PDF has several circuits, scroll to find this design.   __ Circuit Design by MariŠn ätofka, Slovak University of Technology, Bratislava, Slovakia

SC Schmitt Comparator HeA - D -  A simple little Design by Martin Keen and Wilf Rigter __ Designed by Wilf Rigter

Schmidt trigger -  Article is in Dutch __ Designed by Jan Hammer

Schmitt Trigger -  Can also be called AN INVERTER or a SCHMITT INVERTER.  We have animated the circuit to show how the output goes high or low according to the input level.  The animation shows a wide gap between the input levels.  __ 555-Timer

Schmitt Trigger -  This circuit uses a single op-amp and the output is triggered by two different voltage levels.   __ Designed by Andy Collison

Schmitt trigger adapts its own thresholds -  EDN-Design Ideas 03/16/2015    If you need to condition a widely-varying signal, a simple Schmitt wonít work, but this DI will__ Circuit Design by Anthony Smith

Schmitt trigger has dynamic threshold -  06/05/97 EDN-Design Ideas Schmitt triggers usually switch only at predefined static setpoints.  For example, to allow user-defined setpoints, you can use a comparator in a standard hysteresis configuration (Figure 1).  However, the design in Figure 2 allows dynamic setpoints, which are beneficial for variable-noise applications.  This circuit is useful for rejecting noise that fluctuates in amplitude.__ Circuit Design by Isaac Eng, GSI Inc, Ottawa, ON, Canada

Schmitt trigger uses two transistors -  Hereís a DI circuit that displays Schmitt-trigger action and can work at high current or voltage.Circuit Design   Einar Abell

Schmitt Trigger: an unusual -  This is a Schmidt unlike any you have seen before.  It has some unusual propertiessome of which are distinct advantages, some are disadvantages.  There is no 'best circuit'different ways of doing a particular function have different uses.   __ Designed by Richard Torrens

SCR-Controlled Eht Power Supply -  Presented here is an extra-high-tension (EHT) power supply capable of delivering variable DC voltage from about 100 V to 5 kV with load current up to 500 mA.  One way of...___ Electronics Projects for You

Self Powered Sine to Square Wave Converter -  Converts sine to square waves without a power-source Useful as a test instrument for audio purposes __ Contact: Flavio Dellepiane, fladello @ tin.it

Simple Circuit changes improve Schmitt trigger -  05/13/99 EDN-Design Ideas The classical Schmitt trigger circuit that youíll find in textbooks provIdeas some noise immunity, such as for the front end of magnetic pickup in position-sensor circuits(Figure 1a].  You adjust the two threshold levelsePDF contains many circuits, scroll to find this one.   __ Circuit Design by Ron Patrick, ECM, Los Altos, CA

Sine/Square Wave Oscillator for Your Workbench -  It uses a switched capacitor filter IC to give a very good envelope stability.___ SiliconChip

Time-tag impulses with zero-crossing -  24-Jan-02 EDN-Design Ideas A "constant-fraction discriminator" usually performs the time-tagging of impulsive events, which have a peaking time of the signal amplitude.  The implementation of this technique requires a delay in the input signal of approximately the same amount as the signal's rise time.  You can attain this delay by using a coaxial cable of an appropriate length__ Circuit Design by Elio Rossi, Itesre-CNR, Bologna, Italy

Transistor Schmitt Trigger Oscillator -  The Schmitt Trigger oscillator below employs 3 transistors, 6 resistors and a capacitor to generate a square waveform.  Pulse waveforms can be generated with an additional diode and resistor (R6).  Q1 and Q2 are connected with a common emitter resistor (R1) so that the conduction of one transistor causes the other to turn off.  Q3 is controlled.   __ Designed by Bill Bowden

Yield Accurate Absolute Values -  07/05/01  EDN-Design Ideas The circuit in Figure 1 delivers the absolute value of the input signal with an accuracy better than 10 ppm of the full-scale range.  The circuit has low zero-crossing error.  You can use it as an asynchronous demodulator, as a source__ Circuit Design by Marco Pisani, Istituto di Metrologia G Colonnetti, Turin, Italy

Zero-Crossing AC switch oscillator -  The circuit shown will switch on and off a resistive or inductive load up to 800VA with the possibility to adjust both the on and off period.  Switching takes place during the zero crossing of the sine wave.  The switch on point is around the zero crossing but __ Contact: d.dimario @ iol . It

Zero-Crossing Avoids AC Noise -  To properly control AC sources using solid-state devices, you need a pulse to signal the start of the ACís rising edge.  Most of the time, however, tremendous noise levels plague power lines.  There needs to __ Designed by Nick Ierfino, Concordia University

Zero-Crossing Detector -  Circuit Ideas for Designers App Note___ Advanced Linear Devices, Inc

Zero-Crossing Detector Uses Only a FeW High-Voltage Parts -  12/01/11  EDN-Design Ideas You can get isolation with low power consumption using this simple circuit.  The circuit in this Design Idea generates a zero-crossing pulse off the ac mains and provIdeas galvanic isolation.  The falling edge of the output pulse happens at approximately 200 μsec before the zero crossing.  You can use the circuit to safely stop the triggering of a thyristor gate, giving it time to properly turn off.  The circuit generates short pulses only when the mains voltage is approximately 0V, thereby dissipating only 200 mW at 230V and a 50-Hz input.__ Circuit Design by Luca Matteini, Agliana, Italy


Converters: Sine to Square Wave


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