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Questions tagged [schmitt-trigger]

Anything related to Schmitt trigger circuits. Schmitt triggers are positive feedback comparator circuits exhibiting hysteresis.

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What is a Schmitt Trigger and its application exactly?

i would like to ask about what is a Schmitt Trigger and about its application. I searched a lot but still didn't understand it. Please explain step by step and hope you help me in its applications ...
user3213767's user avatar
9 votes
6 answers
922 views

Is a Schmitt-trigger output’s rise time affected by input pulse’s rise time?

I know that a Schmitt-trigger makes rising edge of an input pulse sharper. But is the rise time of the output pulse affected by the input’s rise time? How can this be shown by simulation or shown ...
GNZ's user avatar
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9 votes
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Does the 74LVC1GU04 actually have "Schmitt-trigger action" on its input?

The 74LVC1GU04 is an unbuffered inverter, which (according to the datasheet) is intended to be used in linear mode in applications, such as crystal oscillators and linear amplifiers with negative ...
johnfound's user avatar
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How do I make an opamp comparator work in schmitt-trigger mode?

I want to control a small 12V case fan. I will set values of R1, R2 and R3 so that the fan will work above temperatures 40oC. I understand that in these kind of systems, there will be an indecisive ...
hkBattousai's user avatar
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Disadvantages of Schmitt Trigger Inputs

I'm familiar with the utilization of Schmitt Triggers when interfacing with low slew rate signals / sinusoidal waveforms. In a recent design, I've been scrubbing our FPGA I/O configurations and ...
Krunal Desai's user avatar
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8 votes
5 answers
4k views

Hardware debouncing of key matrix with minimum passive components

I have recently bought this cheap 4x4 keypad matrix. It only has the push-buttons and nothing else therefore I want to add a proper debouncing to it. The debouncing in software is something I want to ...
DEKKER's user avatar
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8 votes
2 answers
3k views

Can multiple Schmitt triggers in series fully debounce a switch?

After dealing with software debouncing for a while, I find it takes a huge toll on the system, so I thought of initially making a hardware debouncer with one Schmitt trigger (74HC14), a capacitor, ...
Mike -- No longer here's user avatar
8 votes
4 answers
20k views

Using CMOS Schmitt trigger inverters in quartz crystal oscillator circuit

In all sources I've seen about quartz crystal oscillators using CMOS inverters there's a note like this: But why Schmitt inverter is needed? Won't classic 74HC04 work?
bokjezd's user avatar
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2 answers
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In a 74HC14 Schmitt trigger IC, unused inputs/outpus

I have a 74HC14 Schmitt trigger IC. I only use one of its I/O pairs, and everything else is not used. I understand that in TTL logic the unused inputs should be set to either high or low to prevent ...
futureshocked's user avatar
8 votes
1 answer
3k views

How does a "speed up capacitor" work in Schmitt trigger?

Hello I'm trying to understand how adding a capacitor across R2 in below circuit increases the switching speed. I don't see how C2 supplies charge to C1. With the additional capacitor C2, it seems ...
AgentS's user avatar
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Why is this derivation of Schmitt trigger circuit's output signal, incorrect?

This is the reference Schmitt trigger circuit. Using KVL, \$V_x\$ turns out to be \$\frac{R_1}{R_1+R_2}V_o\$. Also, $$V_o = A\left( V_x - V_i\right)$$ $$V_o = A\left( \frac{R_1}{R_1+R_2}V_o - V_i\...
Akash Karnatak's user avatar
6 votes
2 answers
356 views

Switching on an SSR on positive voltage and turn it off on negative voltage

I am currently trying to "hack" my way through a door lock, whose PCB cannot be changed. The task is to replace the motor for turning the cylinder with a Solid State Relay. However, the only ...
Sofia Braun's user avatar
6 votes
2 answers
13k views

Comparator with hysteresis equations

I'm trying to be sure I'm computing the values for this circuit right. Here's an example of the circuit I'm trying to build (it's going in a 12 V DC system, so I filled that in already). I have ...
Matthew's user avatar
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6 answers
4k views

Discrete Schmitt Trigger: make output logic level at 0V, not 3V

I designed a Schmitt Trigger with discrete components (using an emitter-coupled pair) that operates with a Low Disable Trigger of around 3.5V and a High Enable Trigger of around 4V on circuit ...
Pan Ziyue's user avatar
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5 votes
5 answers
2k views

Why do TTL pulse generators generate an asymmetrical square wave (unlike CMOS)?

I've read that the asymmetrical (about 1/3 mark-to-space) output waveform is due to input gate characteristics of a TTL inverter, but I want to know more about which characteristics of the TTL input ...
patthew77's user avatar
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3 answers
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Calculating R and C for schmitt trigger debouncer

I've been looking all over the internet to try to figure out the optimal values for R1, R2, and C but couldn't find info. I'm trying to ideally make a debouncer that will work with any button on the ...
Mike -- No longer here's user avatar
5 votes
6 answers
4k views

Positive feedback and unstability

In Wikipedia's positive feedback article it is stated that given the closed loop gain $$A=\frac{a}{1-af}$$ the system is unstable if \$af>1\$. I don't really get this. If \$a=10\$ and \$f=0.5\$ (...
Tendero's user avatar
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1 answer
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Working of Hex Schmitt−Trigger Inverter as a Sawtooth and Square Wave Producer

Can someone explain how a Schmitt Inverter can behave as a Sawtooth (on pin 1) and a Square wave (on pin 2) as produced in a circuit where we have a Capacitor between pin 1 and GND, and a resistor ...
Sherby's user avatar
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What is the purpose of the following inverter topology?

I stumbled upon an Schmitt-trigger oscillator circuit. I can fully understand the principles and its function, but what I cannot fully understand is the chain of inverters after it. In the above ...
Arkoudinos's user avatar
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1 answer
394 views

How do I prolong the reed switch output time

I put a reed switch ( https://en.wikipedia.org/wiki/Reed_switch ) on the handle of a measuring wheel (perambulator). The reed switch will be activated up to around 20 times per second (every 50 ms). ...
phell's user avatar
  • 53
4 votes
3 answers
782 views

Minimizing signal delay when debouncing

I have a mechanical switch that I'd like to use as a signal source for a digital input of a microcontroller. The switch is normally closed, and I'd like to detect the switch being opened as quickly as ...
Florian Ragwitz's user avatar
4 votes
3 answers
3k views

Schmitt trigger - why is there no current over the second transistor?

I'm reading through The Art of Electronics, and I'm trying to wrap my head around a Schmitt trigger. simulate this circuit – Schematic created using CircuitLab Why is there no current over Q2 ...
Maja Piechotka's user avatar
4 votes
4 answers
865 views

Op-amp with Schottky diode

I'm struggling to understand what the sense is of using the two Schottky diodes in this excerpt of a circuit: I understand how a Schmitt trigger works. The diodes ensure that the voltage difference ...
olympus_mons's user avatar
4 votes
4 answers
421 views

Comparator with hysteresis equation for Vmax Vmin

In a scientific paper (Design Considerations for Current Transformer Based Energy Harvesting for Electronics Attached to Electric Motor J. Ahola et. al.) I came across the comparator circuit with ...
Ziegi's user avatar
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4 votes
2 answers
925 views

Why doesn't this schmitt PWM circuit work as expected?

I've designed and built an adjustable PWM generator using schmitt trigger inverters. However, it doesn't seem to be working. Here is the circuit: The capacitors at the bottom are intended to be ...
Sod Almighty's user avatar
  • 1,465
4 votes
2 answers
446 views

In an astable multivibrator, why doesn't negative feedback prevent the output from ever saturating?

What I understand of an astable multivibrator so far is this: The output saturates to one of two extremes, which drives the capacitor in the negative feedback loop to either charge or discharge. Once ...
Anjali Kadambi's user avatar
4 votes
2 answers
421 views

I am facing a problem while designing a Schmitt trigger circuit

I am applying a Schmitt-trigger to the waveform given in the figure below. . This is a 3.5 volt signal and I want to perform thresholding so I use 1.58 volts as upper threshold and 1.17 volts as lower ...
Muhammad Usman 's user avatar
4 votes
1 answer
891 views

Questions on this high frequency sawtooth generator

So I found this very basic sawtooth generator: http://www.radiolocman.com/shem/schematics.html?di=143990 I have a few questions about it: I understand that when the capacitor C_T charges fully to a ...
Dehbop's user avatar
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1 answer
153 views

Improving waveform shape in discrete Pierce oscillator with Schmitt trigger output

I am making a simple clock source using discrete Pierce oscillator with its output attached to high speed Schmitt trigger buffer to get square wave in the final output. I got the circuit for the ...
Muhammad Nour's user avatar
4 votes
5 answers
1k views

How to fix oscillation of an 'over-discharge protection' circuit for a lead-acid battery

I've created a circuit to protect my lead-acid battery from over-discharging. I used the following circuit diagram. Over-discharge protection circuit for a lead acid battery: For understandable ...
sribasu's user avatar
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3 votes
3 answers
949 views

Why is a Schmitt trigger useful for SPI?

I understand Schmitt triggers are a great way to convert a floating or noisy signal to either HIGH or LOW depending on a threshold. It is mentioned in other threads that a Schmitt trigger can help ...
Tommy95's user avatar
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3 votes
4 answers
508 views

Schmitt trigger transistor duty cycle

I built this Schmitt trigger using transistors (2N3704). Input is a square wave coming from an OCXO, 1 MHz, 50% duty cycle. I obtain a square wave with 70% duty cycle. What can possibly be the cause?
Ken90's user avatar
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2 answers
1k views

LTspice simulation of LM311 comparator with hysteresis not behaving as expected

I am trying to simulate the following comparator circuit with LTspice: The LM311 comparator was intended to be used with hysteresis, same as the circuit shown in this graph (designators are the same):...
Zhi's user avatar
  • 41
3 votes
1 answer
1k views

Why is this BJT Schmitt trigger producing a sine wave?

I am trying to build a Schmitt trigger from a pair of BJTs to convert a sine to a square wave. The sine wave is from a Colpitts oscillator running at over 150 MHz. I want to measure the ...
brendans-bits's user avatar
3 votes
2 answers
4k views

How can I test a hex Schmitt trigger?

Yay, me...I just got done soldering my first surface mount IC. Because I know how volatile heat can be, and with how close the tip of my iron was to the IC (especially without a socket!), I'd like to ...
dwwilson66's user avatar
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3 votes
3 answers
2k views

How to determine the saturation level when an opamp schmitt trigger starts worknig?

The Opamp inverting schmitt trigger is constructed as shown. The output signal is: So I ask why is the output at the start of operation saturated to positive? Also, if the input voltage is moved ...
Raafat Abualazm's user avatar
3 votes
3 answers
615 views

Why doesn't the following circuit have negative feedback?

Consider: The Sedra book says that it's a Schmitt trigger, so there is positive feedback, but why doesn't it have negative feedback as well?
FY Gamer's user avatar
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2 answers
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How to build a Schmitt trigger using transistors?

I understand that Schmitt trigger is a comparator circuit with hystersis and that it is used to convert signals from analog to digital and to remove noise from a signal using positive feed back. ...
razzak's user avatar
  • 490
3 votes
1 answer
753 views

Transistor Schmitt trigger vs opAmp Schmitt trigger

Schmitt trigger was originally implemented by using two transistors long time ago. Are there any advantages using Transistor Schmitt trigger instead of using opAmps?
user16307's user avatar
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3 votes
2 answers
552 views

Trouble with Schimtt trigger settings for varying sinusoidal inputs

To make my problem easier to describe, I drew the above figures (abbreviated as Fig.). The sinusoidal input comes from a rotating device, from a small alternator(a permanent magnet AC generator). ...
user16307's user avatar
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3 votes
3 answers
2k views

Flip a Schmitt-Trigger when current flows through a Zener diode

I am trying to design a circuit using an intermitent power source (a bicycle hub generator), which is rectified and filtered, and regulated at 6,8V. Now I want to "detect" when the power source is ON ...
heltonbiker's user avatar
3 votes
1 answer
700 views

Solving Schmitt trigger circuit using the superposition theorem

In order to solve a Schmitt trigger circuit implemented with an op-amp (or a comparator) connected in positive feedback, this wikipedia page uses the superposition theorem. My question is : why can ...
anpar's user avatar
  • 135
3 votes
4 answers
5k views

555 Schmitt Trigger works well with CMOS LMC but not NE555?

I have an NE555 (the non-CMOS version) running in astable mode at 118Khz. I have the output pin3 connected to input for a second 555 running as a Schmitt Trigger to invert the signal. What I found is ...
JamesHoux's user avatar
  • 901
3 votes
1 answer
484 views

Some questions regarding the resistors and capacitors around an opamp

I have been dealing with the following part of a circuit for a while: But for the sake of curiosity I have some more questions left not specifically about this particular circuit but for all similar ...
user16307's user avatar
  • 12.2k
3 votes
1 answer
263 views

Relaxation oscillator with two time constants

I have the following circuit and I have to find the duty cycle of the output signal and its frequency: I figured out that if \$v_{cond} > 0\$, then D4 will be forward biased and D3 reverse biased, ...
Laura_F's user avatar
  • 33
3 votes
1 answer
518 views

Do Schmitt-trigger specs give requirements to avoid metastability?

Although Schmitt triggers are not usually regarded as latches with setup/hold constraints, a Schmitt trigger is functionally a sort of latch which is forced one way when the input is above a certain ...
supercat's user avatar
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2 votes
3 answers
1k views

A question about positive feedback resistor in a Schmitt trigger

In many tutorials when explaining hysteresis what I read that when the output is high R3 becomes in parallel with R1; and when the output is low R3 becomes in parallel with R2. Above is a depiction of ...
user16307's user avatar
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2 votes
3 answers
736 views

Why is my op-amp pulse generator (LF353) delivering way less voltage (±2 V) than the voltage supplies of the amplifier (±15 V)?

I had to design the following circuit as a pulse generator so that if I vary the resistance the frequency will vary as well. It's defined by the frequency expression: $$f=\frac{1}{2R_4C_1\ln(3)}$$ ...
ronny's user avatar
  • 83
2 votes
2 answers
987 views

CPLD based Pierce oscillator

I want to make a clock generator for Altera EPM240T100C5N using the CPLD itself as a Pierce oscillator. This CPLD has Schmitt trigger inputs so I guess this should be possible. What I`m not sure about ...
hidefromkgb's user avatar
2 votes
4 answers
469 views

Using a Schmitt trigger IC vs making one from op-amps or transistors

In a professional setting, what is the benefit of using a Schmitt trigger IC as opposed to making one from op-amps or transistors? In a high volume application, wouldn't an op-amp implementation be ...
Jason's user avatar
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