Electrical Engineering Stack Exchange
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Questions tagged [astable]

119 questions
22
votes
5 answers

Astable 555 circuit not oscillating

I'm a complete beginner to electronics, but I'm trying to follow Ben Eaters video series "Building an 8-bit computer". I tried to do the first part of an astable 555 timer, but the LED does not oscillate and on top of that the timer draws A LOT of…
Mr Filp
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4 answers

How does this astable multivibrator circuit with FETs work?

I am having trouble understanding this schematic. I do understand that it is pretty simple, but I just can't seem to get my head around part of it. The schematic is a more complicated version of an astable multivibrator. I understand how an astable…
SadlerJ
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7
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3 answers

Adding Diodes to Transistor Astable Multivibrator; 1N5818 Schottky diodes work but 1N4148 diodes don't; can't figure out why

I am an avid electronics hobbyist, not an electronics engineer. I built a transistor-based astable multivibrator circuit and then fed its output to an op amp buffer amplifier which then drove an 8 ohm speaker. Here is an image of the circuit…
Brock R. Wood
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2 answers

555 Astable : Separate charge and discharge resistors?

The 555 astable oscillator seems to be usually implemented with one common resistor between the charging and discharging paths of the capacitor. Is there something wrong with putting one resistor for the charging path, and one for the discharging…
Strayed101
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4
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2 answers

555 astable resistor location

When looking at example schematics of a 555 astable circuit, they all show the two resistors in series with the C. I'm wondering how this differs from the schematic I've created below; Here R6 is used to load C3 and R5 to discharge, which should…
Frank
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4
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4 answers

BJT astable multivibrator frequency increasing with voltage

I'm trying to get a 27V 120Hz square-wave, so I tried this circuit : I get a decent 128Hz signal with 9V, which is close enough. However, if I increase the input voltage past a certain point, the frequency increases too. For 27V, it is about…
Bastien
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4
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2 answers

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 there is a discrepancy between the inverting and…
Anjali Kadambi
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4
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2 answers

555 Astable Timer produces incorrect period/frequency

I am building a 555 astable timer circuit for a course which must match the BPM of a song. The song has a BPM of 104, which requires a timer frequency of roughly 1.733 Hz. The circuit looks as follows: (the green wires go off to the left onto…
battr
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4
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2 answers

Naive VCXO design - runs at 3rd harmonic, I need the base freq

Consider this a hobby question. (How do you call a hobby project on the fringe of your nominal work? A skunkworks job?) I mean to say that I'm not an EE design pro. I'd appreciate your opinion about an Xtal oscillator I'm playing with. Long story…
frr
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4
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1 answer

astable multivibrator: capacitor polarization

Looking at this circuit, I'm wondering if the capacitor polarization "+" is correctly draw. Assuming T2 is in cut, T1 is on, left capacitor will have a 0.7v in its right side (connected to T1 emitter) and Vcc(without load) in its left side (connect…
pasaba por aqui
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4
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2 answers

Circuit for flashing LEDs for airplane model wing, tail and beacon lights using 555

I am working to make flashing LEDs for my airplane model. There are three LED pulse sequences on the picture below where to flash LEDs respectively. So how do I design a circuit using an astable multivibrator using the IC 555 timer? How do I design…
Ajas
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4
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2 answers

Astable 555 frequency problem

I'm trying to build an oscillator circuit for driving several IR LEDs at 38 kHz 50% duty cycle. The circuit layout I used is shown below.(Source link: http://www.electronics-tutorials.ws/waveforms/555_oscillator.html ) (Pin 7 is not connected to…
packt
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4
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1 answer

Astable 555 Timer creates longer pulse when just turned on

I have a question regarding the behavior of a 555 timer circuit that I have made. It is depicted below. Now, here is some interesting behavior, I wrote a program on arduino that measures the lengths of the pulses from this 555 timer. Here is the…
Anthony Dito
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3
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1 answer

Frequency of astable multivibrator built with inverters (NOT gates)

I've assembled the following astable multivibrator (a.k.a. astable oscillator) circuit: It generates a square wave (as expected), but the output frequency isn't predicted well by the formulae that I've come across for this circuit. For example,…
Reign of Error
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3
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3 answers

Why does output become inverted in op-amp astable multivibrator?

This is the circuit I'm considering. I understand how Vo becomes Vsat, and Vn increases until it is equal to Vp, which is R1/(R1+R2)·Vsat. Many people say when Vn slightly exceeds Vp, Vo is inverted. However, my question is: how can Vn exceed…
user18926955
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