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25 votes
Accepted

Hardware debouncing of key matrix with minimum passive components

Let's be clear about this. If you have a keypad matrix you are already using processing power to apply sequential logic voltages to the rows or columns then reading the columns or rows back in order ...
Andy aka's user avatar
  • 464k
16 votes

Can multiple Schmitt triggers in series fully debounce a switch?

Can multiple Schmitt triggers in series fully debounce a switch? A single Schmitt trigger with a analog filter in front of it can be used for debouncing. However, after that Schmitt trigger, the ...
Olin Lathrop's user avatar
16 votes
Accepted

Does the 74LVC1GU04 actually have "Schmitt-trigger action" on its input?

This is a copy-paste error. All other (buffered) parts in the 74LVC series have schmitt-trigger inputs, but the 74LVC1GU04 in particular does not. They simply forgot to delete that line from the ...
Jonathan S.'s user avatar
13 votes
Accepted

Can multiple Schmitt triggers in series fully debounce a switch?

Using Schmitt triggers in series would not further reduce bounce. Consider the filter: The input is (U). The red line is a 50% threshold, the output of which is seen as signal (A). It bounces each ...
Bort's user avatar
  • 5,172
12 votes

Can we declare Schmitt triggers to have memory? Can we call their output levels states?

Yes, "memory" in the sense of "this system is not memoryless" is any difference in behaviour that depends on previous internal or external state. Since the exact idea of a Schmitt ...
Marcus Müller's user avatar
10 votes

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

DISCUSSION I don't know if this will help you at all, but if you are reading The Art of Electronics, then you will also almost certainly read (in about 20 pages yet) about the long-tailed pair ...
jonk's user avatar
  • 78.3k
9 votes

Minimizing signal delay when debouncing

The best way to handle this is to debounce the signal in software with your microcontroller. This is cheap, simple, and gives you maximum versatility in terms of your debounce algorithm. Here's an ...
Drew's user avatar
  • 7,119
8 votes
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Why doesn't this schmitt PWM circuit work as expected?

I'm afraid your simulator is lying to you, by failing to take into account the actual input characteristics of the 74LS14. According to the datasheet (Section 6.5 on page 5), note the values for IIH (...
Dave Tweed's user avatar
  • 175k
8 votes

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

The positive feedback path provides the hysteresis that makes it a Schmitt trigger. However, it also forms an RC filter between the parasitic capacitance C1 and the resistor R1||R2. It's possible ...
Cristobol Polychronopolis's user avatar
8 votes
Accepted

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

I'm aware that something might be wrong with my circuit but I don't know what that is A 100 Ω load (R4) will scupper the output signal levels for an LF353: - The same is true for the LF353-N: - ...
Andy aka's user avatar
  • 464k
7 votes

CPLD based Pierce oscillator

This CPLD has Schmitt trigger inputs so I guess this should be possible. Actually, if it has Schmitt trigger inputs it makes it impossible. A Schmitt trigger would just about guarantee that the ...
TimWescott's user avatar
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7 votes
Accepted

Why is this derivation of Schmitt trigger circuit's output signal, incorrect?

Point 1 The Schmitt trigger has hysteresis. Hysteresis implies that the circuit has memory. It remembers it last state. For a system with memory, you cannot write \$V_o = f(V_{in})\$. It should be of ...
AJN's user avatar
  • 3,891
7 votes

Can we declare Schmitt triggers to have memory? Can we call their output levels states?

A latch is like the simplest form of memory. If you configure a Schmitt trigger as a latch, it is not a stretch to call it one bit of memory. But any buffer can be set up as a latch. I guess I am ...
user57037's user avatar
  • 29.4k
7 votes
Accepted

Minimizing signal delay when debouncing

If you insist on a H/W solution, a diode will make the charging/discharging of the cap asymmetrical. The delay will be a few microseconds. The recovery time will be a few milliseconds. simulate this ...
Mattman944's user avatar
  • 16.4k
7 votes

Opamp-based Schmitt trigger

The output of inverting Schmitt trigger has 180 degree phase shift when compared to non-inverting Schmitt trigger. No, it inverts. That's not a phase shift, unless your signal is a square wave with ...
Marcus Müller's user avatar
7 votes

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

Yes, it will likely be affected somewhat. Intuitively you would expect that because at slow input change rate you are depending on the positive feedback to drive the output slew rate. For a fast input ...
Spehro Pefhany's user avatar
7 votes
Accepted

Why is a Schmitt trigger useful for SPI?

SPI is a synchronous bus, which means that the number of clock cycles generated by the controller needs to exactly match the number seen by the device. Running a 20-MHz square wave over a meter of ...
Dave Tweed's user avatar
  • 175k
6 votes

Schmitt Trigger Comparator 0 - 5V

The LM358 op-amp will not swing it's output to the positive supply rail. The top "transistor" in the package is configured as a Darlington-pair and this is your problem: - Even if the base of Q5 ...
Andy aka's user avatar
  • 464k
6 votes
Accepted

How is a latch different from Schmitt Trigger?

They differ in the level of the signal that is required to change their state. In a Schmidt trigger, a relatively small, well-controlled change of signal level is needed. The input is designed to ...
Neil_UK's user avatar
  • 169k
6 votes

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

Two reasons. First, a TTL input is actually an output. It sources a current that must be shunted to ground to be seen as a logic 0. This current affects the charging rate of the timing capacitor, ...
AnalogKid's user avatar
  • 21.2k
6 votes

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

CMOS Schmitt triggers have the two threshold voltages at \$\frac 1 3 V_{DD}\$ and \$\frac 2 3 V_{DD}\$. Furthemore \$V_{OH}=V_{DD}\$ and \$V_{OL}=0\$. Since this is symmetric with respect to \$V_{DD}/...
next-hack's user avatar
  • 5,367
6 votes

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

The National (now TI) LM741 really is not well characterized to run off of a single \$5\:\text{V}\$ supply rail. The LM741 datasheet suggests that with your loading, you are guaranteed to get within ...
jonk's user avatar
  • 78.3k
6 votes
Accepted

CPLD based Pierce oscillator

I do not recommend this approach. You may get some circuit to oscillate under some conditions but you may very well have problems with jitter, unreliable startup and off frequency operation. You ...
Michael Karas's user avatar
6 votes
Accepted

Anyway to reduce pulse trigger time width without using ne555timer

Your comparator circuit is flawed because of this: - I've marked a red arrow showing what you have done wrong when using an op-amp with an AC signal source. You are attempting to feed in an input ...
Andy aka's user avatar
  • 464k
6 votes
Accepted

Suitable IC for 3.3 V to 5 V level conversion with a Schmitt trigger input

When powered from 5V, any HCT series logic gate has input levels compatible with 3V3 logic and 5V output levels. 74HCT14 has Schmitt trigger inputs. 74ACT is faster, has higher output current, and ...
bobflux's user avatar
  • 79.5k
6 votes
Accepted

LTspice simulation of LM311 comparator with hysteresis not behaving as expected

What could be the cause of this behaviour? Thanks in advance! The emitter should be connected (via a resistor or not) to ground and not 5 volts: - And, the collector normally has a pull-up resistor ...
Andy aka's user avatar
  • 464k
6 votes
Accepted

Schmitt trigger transistor duty cycle

1MHz may seem like a really low frequency but you'll see a lot of effect from storage time in saturated BJTs at that frequency. Here is your circuit (but with 2N3904s substituted since I don't have a ...
Spehro Pefhany's user avatar
6 votes

Op-amp with Schottky diode

The diodes conduct hardly at all near the switching point, which is where the two input voltages are almost equal (within a mV or so for most op-amps), so they can be ignored when analyzing the ...
Spehro Pefhany's user avatar

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