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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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?
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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 ...
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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 ...
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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 ...
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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\...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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). ...
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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 ...
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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 ...
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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 ...
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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 ...
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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.
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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 ...
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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 ...
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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\$ (...
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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 ...
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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 ...
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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):...
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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 ...
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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 ...
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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 ...
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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?
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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).
...
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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 ...
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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?
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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 ...
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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. ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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)}$$
...
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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 ...
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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 ...
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How to implement programmable Schmitt trigger?
I am trying to build a Schmitt trigger that would allow adjusting High and Low threshold values with a microcontroller.
simulate this circuit – Schematic created using CircuitLab
I could ...
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How to understanding min/max input values of Schmitt Trigger from datasheet
I am having some difficultly understanding the values described in this product sheet for the SN74AHCT14 Schmitt Trigger Inverter:
http://www.ti.com/lit/ds/symlink/sn74ahct14.pdf
Given a Vcc of 4.5V,...
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TTL Schmitt trigger vs TTL in relaxation oscillator
as far I know, the schematic works also with a simple TTL NOT gate.
Is there any special reason to use the Schmitt Triggers?
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A question about a debouncing circuit
I was reading a tutorial on debouncing the outputs of a rotary-encoder which are read by a micro-controller.
Below is the circuit given:
The writer of the tutorial claims the following:
"In the ...
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Ideal v. Non-Ideal (?) Schmitt Trigger Transfer Curve
I was doing an assignment about op amps and I had to simulate a Schmitt Trigger and plot its transfer curve. The assignment handout gave me a plot to compare the curve with. Here are both the plots, ...
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How to derive the node voltage for this comparator with hysteresis?
I have the following circuit. U26 is a simple unity buffer and U15 is just a dual comparator.
I want the top comparator to compare the battery voltage (VBAT/2) on the inverting input with 2.0V ...
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