Questions tagged [schmitt-trigger]

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

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34 views

Schmitt Trigger voltage divider

Could someone please explain to me when and why should we add a voltage divider at the inverting input of a Schmidtt Trigger?
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5answers
178 views

High Frequency Square Wave Generator

I want to generate square wave but there are some challenges. Rise time should be less than 2ns as well as fall time (for 0V to 5V). Duty cycle is not so important it should stay high like 40 ns. I am ...
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2answers
55 views

Hardware debouncing using 74LS14 - inverter input does not drop below 800 mV

I just recently started dabbling with electronics, so probably I just made some beginner's mistake. Here's my problem: I want to debounce a switch in hardware. During my internet research, I found ...
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1answer
49 views

How to use op-amp circuit as a threshold trigger

I recently built the following circuit: In case you can't tell, it has 23 volts on the power rail and VEE is connected to ground. I don't have any feedback on the output. I have a simple voltage ...
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4answers
699 views

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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0answers
61 views

Schmitt trigger output waveform coming as sinewave

I am new to Proteus. I tried simulating an easy circuit which was a Schmitt trigger using an op-amp. After simulation, the output waveform was an sinewave instead of rectangular wave. Any idea where I ...
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4answers
199 views

Push button de-bouncing, nothing works. [Please, only answer if you have actually done it (recently or often enough) to know for sure!]

I see a lot of text on the internet and here telling us how to de-bounce a switch, in my case a push button. But I have tried all these circuits and I find that nothing other than a 555 monostable ...
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3answers
88 views

Positive edge detection triggers on negative edge too

I have 74LS170s and 74LS670 register files which have the trouble that they are not edge triggered but like SRAM accept data for the entire duration of the write gate being low. So, I have the ...
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0answers
28 views

DC Supply voltage drop in a Schmitt trigger circuit

I developed a Schmitt trigger using IC NE555P. I supplied a Vcc of +6v from a DC source. My input is a sinusoidal wave (peak-peak = 4V). First I set the voltage in DC source (+6v) and when I connect ...
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0answers
50 views

Schmitt trigger using NE555P gives wrong output

I am trying to create a Schmitt trigger using NE555P to generate square pulses from some periodically changing signals. I used the following circuit diagram and applied some sinusoidal waves (3.3v). ...
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1answer
67 views

Anyway to reduce pulse trigger time width without using ne555timer [closed]

Is there any other way to reduce the time width of the trigger pulse wave without using 555timer?
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4answers
133 views

Is this input-output relation correct? Schmitt trigger

OK, operational amplifier will want to keep node A at GND level. It will try to set its output so that the condition (inverting input potential = non-inverting input potential) is satisfied all the ...
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0answers
73 views

Is this an elegant approach for a simple, debounced tank level controller?

I am interfacing some industrial (24v) process control equipment to some new projects in the embedded realm of electronics (3.3/5V small signal) and am coming up with some simple solutions for ...
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2answers
98 views

Schmitt trigger offset voltage

I found this circuit which generates an offset voltage to the hystersis (so the threshold voltages are for example not -3V and 3V but -2V and 4V). It would be the same as if you remove R1 and put a ...
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0answers
26 views

Temperature Effect on Schmitt Trigger Threshold Levels

I have found minimal information on the internet, as well as in multiple data sheets I have looked at. I'm designing for a large temperature range of 150°C. I require a fairly consistent voltage ...
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1answer
87 views

Open collector / drain question

I'm trying to to find the best way to force an inverting amplifier to postive saturation with a gate input, but otherwise leave the function of the op-amp intact. I've come up with a few ways to do ...
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1answer
91 views

Op amp as a Schmitt trigger

I am working on a project which needs a Schmitt trigger. I designed it using IC UA741. I am using a single power supply of 9V. I am grounding the V-. Here is my design. The circuit works perfectly ...
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1answer
67 views

schmitt trigger and noise

I know that a Schmitt trigger is used to reduce noise in a circuit, but why does noise need to be reduced. How does noise effect the overall circuit and what benefits do you achieve by reducing noise ...
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2answers
111 views

74HC14 waveform question

I am trying to get more familiar with using a 74HC14, as an experiment I have an ldr set up in a voltage divider configuration and the center tap goes to the input of the 74HC14 input 1. I have all ...
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1answer
41 views

Concept of Hysteresis and Threshold point in Schmitt Trigger

I understand the concept of Schmitt Trigger where there is 2 transition threshold points so that input changing between the hysteresis would not create output transitions . The very first observation ...
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1answer
210 views

74HC14 for debouncing: output is too low with Vcc=3.3V

I'm trying to make a keypad for STM32 MCU using a 74HC14D.653 for debouncing. Datasheet says that it can be fed with 3.3V Vcc so I will not have to make level-shifting between it and MCU. The circuit ...
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1answer
49 views

Calculation of a feedback resistor in an inverting shmitt trigger

This is taken from a frequency counter circuit based on a schmitt trigger comparator . The frequency counter has a noisy immunity threshold of 100mV. How would you calculate the Rfeedback resistor ...
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4answers
131 views

Can't get this schmitt oscillator to work…did I goof somewhere?

Below is my attempt at a schmitt oscillator circuit that uses a 74HC14 and lights up three LEDs in sequence. I built it on some breadboard, but nothing lights up. I'm really at my wits end...can ...
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3answers
62 views

Initial pluse from schmitt trigger switch debouncer

I want to use a momentary, normally open, SPST switch to act as a clock pulse on 16x2 character display. Of course, my switch has some bounce so I was looking at debouncing circuits and I always see ...
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1answer
100 views

Why there is RC filter between optocoupler and schmitt trigger?

I want to use schmitt trigger after optocoupler to have clean signal and connect it to MCU.why there is RC filter between optocoupler and schmitt trigger in many designs? How should i connect ...
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2answers
156 views

Purpose of the Schmitt trigger in this midi circuit

I came across an instructable about using midi with a raspberry pi and I was a bit confused about the first circuit from step 2. What are those Schmitt triggers for and are they really necessary? . ...
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2answers
179 views

Schmitt Trigger Level Translation from Encoder

This is my first time using an encoder as well as a Schmitt trigger. Typically, I would do debouncing in software, but I want a hardware solution for the sake of learning how to do so. The encoder I ...
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1answer
888 views

How to power schmitt trigger in LTspice with negative voltage?

I use CD40106 model in LTspice for schmitt trigger, but the circuit I want to simulate has -5 and 0 V levels, CD40106 only accept positive value for VDD and there is no other param to change the value ...
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3answers
214 views

Generating square wave to be inputted into a MCU

There are signals like below picture inputted to MCU STM32f103: (Offset DC about 800mV, Vmax = 2.4V, f = 66 Hz) I want to change it to a squar wave from 0V to 3.3V being accepted voltage range for my ...
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1answer
98 views

Understanding this comparator circuit

This is what I understand about the circuit: It's not a window comparator exactly as the outputs are not connected together and the inverting inputs are actually connected together. They look like ...
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1answer
124 views

Op-amp circuit hysteresis calculation

Given this circuit, I have to find \$\frac{V_2}{V_1}\$ as well as the magnitude of hysteresis. I don't need a full solution. Any hints to approach this problem would suffice. So far, I know the left ...
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1answer
99 views

Pulse width stretching of the 0 pulse with a constant T [closed]

I have a digital output with varying pulse sizes and I want to design an IC to stretch the 0 output for a constant T+ "0" pulse time (as in attached picture). I have tried using a monostable ...
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3answers
234 views

Schmitt triggers hysteresis symbols

So we're studying Schmitt triggers at university and we got these representations. Searched them on google for more info and got other representations. Now I'm confused. Can anyone help me with some ...
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1answer
137 views

schmitt trigger causes noise

I am trying to get a 74HC14 hex inverting schmitt trigger to work. First thing I did was connect it to a power supply. When I connect the Vin and Ground ports to my bench power supply (5V), some ...
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2answers
772 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 ...
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1answer
96 views

Noisy rising and falling edges at the output of a schmitt trigger circuit

I wanted to replicate a comparator circuit to PCB and I later noticed that I mistakenly swapped the inverting and non-inverting inputs. The comparator used is LM2903. Surprisingly the board was still ...
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1answer
93 views

Function generator design

So i was asked to design a function generator that eventually produces a sine wave at the output of the circuit and this is what i have come up with so far. A Schmitt trigger and then an integrator ...
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1answer
242 views

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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2answers
1k views

Calculating resistor values for a Schmitt Trigger and LDR circuit

I am trying to make a light sensing circuit which has hysteresis. I want an op-amp (LM358) to output logic 1 (12v) when the light level rises above 250 lux, and output logic 0 (0v) when the light ...
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0answers
53 views

Driving transistors without using MCUs

I'm trying to drive transistors with just a push of a button without using a MCU. The circuit I drawn drives different transistor on every button push and resets back. First part is a debounce circuit ...
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3answers
162 views

Really occasional malfunction of the Schmitt-trigger input

I'm using some Schmitt-trigger inputs for debouncing the interrupt problems. Referring to above circuit, the circuit has a RC circuit and the output of the RC circuit goes to the Schmitt-trigger IC(...
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2answers
158 views

Was my circuit victim of capacitor self-resonance?

In order to generate a short pulse off a permanent constant current signal, I made this circuit. It works well except that it created a very high frequency ripple which wreaked havoc all over the ...
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1answer
269 views

STM32L0: Fast processing of an analog sinusoidal signal

I have an embedded system based on a STM32 ARM Cortex M0+ microcontroller (STM32L051K6) and want to use it to convert an analog sinusoidal input signal into a digital pulse signal and do some SW ...
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5answers
445 views

Schmitt Trigger hysteresis

I am studying comparators and Schmitt triggers. And I did not find anywhere how to choose the value of hysteresis. I understand its purpose and I know how to calculate it. But what value is needed for ...
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2answers
95 views

Voltage appears on comparator input

I have made a pcb . A part of the circuit is the Schmitt trigger comparator seen above . The positive feedback resistors are chosen to give the noniverting input values from zero to 0.5 volts . ...
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0answers
187 views

Flashing an LED with Schmitt trigger

I'm trying to build the above circuit, which is supposed to flash an LED with a schmitt trigger (with the possibility to vary the frequency with the knob of the 47kOhm potentiometer). I don't have a ...
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1answer
342 views

Schmitt Trigger: Problems between theory and reality

I want to say that I am not a native English speaker so you may find some writing errors. Also, I am just learning electronics, so sorry if some questions are poorly formulated. I am trying to build ...
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282 views

Schmitt trigger oscillators interfere with eachother (74HC14)

I am using a single 74HC14 (hex schmitt trigger) to implement three oscillators. I now have a test build ready and encounter problems. See schematic, it shows component values. Also proper 5V power ...
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2answers
155 views

Need help understanding an electronic oscillator (Schmitt trigger + capacitor) [duplicate]

When we use this circuit, the LED blinks. I know an inverter transforms high to low voltage and low to high voltage, but here the voltage source is connected to the inverter all the time so the ...
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0answers
43 views

Simplest schmitt trigger with fewest part count for microcontroller

I own several AT89C4051 microcontrollers and I'm currently trying to read signature bytes of the micros that I probably broke (by applying 7.2V to the VCC pin before noticing the 5V regulator became a ...