Questions tagged [schmitt-trigger]

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

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77 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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25 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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85 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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32 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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71 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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39 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
124 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
40 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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44 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
78 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
122 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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311 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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165 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
88 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
116 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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57 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
144 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
94 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
732 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
69 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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75 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
197 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
419 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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51 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
116 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
142 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
187 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
321 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
64 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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105 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
248 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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0answers
186 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
122 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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40 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 ...
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1answer
655 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 ...
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1answer
42 views

Determining U_ref on Schmitt Trigger

If I have only starting values a U_high=3V and U_low=2V (pulse signal on V3 on schematics), can I determine a U reference, that's given us on the inverting input of the op. amp.? My calculations were:...
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1answer
88 views

Op. amp. with integrator - enough values to start?

All the red-circled values (Uref, C2, R31 and R36) are missing. I'm supposed to calculate them, but I think there's at least one value missing. Shouldn't Uref be known to calculate the rest of the ...
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3answers
453 views

Schmitt Trigger not reaching full saturation

I'm trying to develop a sensor based on the optoelectronic device CNY70. I want to filter the signal in order to be read by a microprocessor, where the threshold to change between logic levels could ...
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2answers
191 views

Need help to increase schmitt trigger sensivity in a circuit

I need help on a circuit I've designed to detect hits on a piezo sensor on a drum. It uses an opamp with 2 channel, on goes to a schmitt trigger, the other to the ADC input on the XMEGA ...
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2answers
132 views

Schmitt trigger inverters or regular inverters for clean high speed data processing

I made a circuit in which data is passed in from phototransistors (part# PT334-6C) into a microcontroller (part# AT89C4051) serial port via schmitt trigger inverters (part# 74HC14) and a demultiplexer ...
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1answer
625 views

Schmitt trigger with 741 op-amp not behaving as in simulation

I am implementing a Schmitt trigger using the circuit shown below. This circuit consists of one LM741 op-amp, which acts as an asymmetrical Schmitt trigger with a single power supply. According to ...
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301 views

cd40106 Problems

so im trying to make this simple oscillator using ic cd40106 without any succsess. it's the usual astable multivibrator configuration using a 9v pwr supply, 220k resistor and a 2.2uf capacitor, the ...
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2answers
390 views

Why do I get a triangle wave in this Schmitt trigger oscillator?

I'm trying to design a function generator that can generate square, triangle and sine waves, with frequency varying between 100Hz and 100kHz. The circuit in the blue box is supposed to be a schmitt ...
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2answers
718 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 ...
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1answer
1k 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 ...
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136 views

Analytically obtaining the hysteresis of an opamp Schmitt trigger with RC network in its inverting input

This is a follow-up from here. I have got the following Schmitt trigger circuit implemented already on a breadboard. As seen, the input signal at the non-inverting and inverting terminals of the op ...
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1answer
50 views

Strange state in input at the amplifier

I have this schematic, an invert Schmitt trigger attached to the RC component to create a triangle wave. It's an oscillator. The two oscillators go in to the amplifier, but I don't understand why I ...
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1answer
294 views

Comparing two variable voltages with hysteresis

All of the designs I have seen for adding hysteresis to a comparator (Schmitt triggers) assume that one of the two inputs to the comparator is set at a fixed reference voltage (typically with a ...
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1answer
228 views

Are Schmitt trigger and peak detector comparator the same?

Here is a peak detector comparator schematic ,its symbol,and its simulation.I have some question about them. First,we all know the Schmitt trigger symbol is the same as the second picture,so are ...
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3answers
495 views

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 ...