Questions tagged [astable]

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Astable multivibrator small capacitor values

Is there a method to determine the values for the resistances? below shows when R1=R2 << R2=R3 and the capacitance is 10uF and the circuit works perfectly. However if I try to reduce the ...
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1 vote
4 answers
189 views

Power transformer circuit using H-bridge doesn't work as expected

I am trying to step up my AA battery's voltage (which is 8 volts in total) using an ignition coil (which is rated for 12 volts input.) To drive the coil I am using an H-bridge at a frequency of 50 kHz ...
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3 votes
4 answers
280 views

Low amplitude output in Opamp square wave generator

I have made a square wave generator using an OPamp in positive feedback. The generator was designed to output a frequency of above 200KHz, so I chose the values of 200ohm and 0.01uF for the RC circuit ...
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0 votes
4 answers
209 views

CD4047 only has OCS output when operated in astable mode

I'm trying to build a simple astable multivibrator using a CD4047. I try to demonstrate using 3 LEDs on the OSC, Q, and Q` pins. Following is the circuit I built (copied diagram): The only difference ...
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6 votes
2 answers
702 views

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 ...
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4 votes
4 answers
615 views

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 ...
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  • 144
-3 votes
1 answer
123 views

precise 50 Hz oscillator [closed]

I need an astable multi-vibrator at exactly 50 or 100 Hz with exactly 50% duty cycle. using circuits like 555 can't give me that with the common well-known values of components R and C , let alone the ...
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2 votes
1 answer
267 views

Why does the output of my astable multivibrator using an op-amp turn into a triangular wave?

I've designed an astable multivibrator for square wave generation using the LM741 op-amp, as showen in the following image: Now I've played a little with the frequencies it can output. As shown in ...
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0 votes
2 answers
131 views

How to limit the output voltage of an op-amp astable multivibrator

I'm trying to make a square wave generator with an adjustable range of output signal amplitude (between 0 and 5V) using an LM741 op-amp and the following circuit: The thing is, VOUT is limited by the ...
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2 votes
3 answers
101 views

555 Astable output staying high

I have a ICM7555 with a 12 V supply in an astable circuit. When ENABLE goes high, I want my output to be high for a given amount of time, then carry on as a normal astable from there. So I have a ...
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  • 117
0 votes
4 answers
184 views

How to set the initial conditions of an astable multivibrator

Consider the following oscillator circuit: I have this running and oscillating at about the frequency I want. However, when first powering it on, one of two things happen: Both LEDs momentarily ...
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1 vote
2 answers
136 views

Astable multivibrator malfunctioning on circuit board

Here is the circuit that I've built on my project board (GL-12) Here is a schematic: Note: I'm using BC107B transistors instead of BC547 as they are quite similar. To test the circuit, I added two ...
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2 answers
153 views

How to actually calculate the rise time for a square wave generated by an Astable Multivibrator?

If I have an astable multivibrator like the one shown in the picture, how do I actually calculate the rise time for the output square wave? I know that it's the time required to change from the low ...
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2 answers
156 views

What actually causes the distortion in the output wave due to an Astable Multivibrator?

I've witnessed that the output square wave from an astable multivibrator using two BJTs has its edges rounded during the rise up time(just as it is seen in fig. 1). Across resources, I've come to know ...
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  • 121
1 vote
1 answer
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Astable multivibrator not producing a square output wave, using two BJTs

I've been trying to build an astable multivibrator circuit using two BC547B NPN transistors. I know how to build one using a 555 timer, but I'm having some problems using transistors. I should've ...
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  • 121
2 votes
4 answers
284 views

Would using the output of a 555 timer to charge/discharge its capacitor work?

Background I'm relatively new to electronics and playing around with a 555 timer. I found that for astable operation, all sources I've seen recommends the following design (with different resistor and ...
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  • 143
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2 answers
387 views

Astable 555 circuit always on, not oscillating

It has been quite a while since I've used a breadboard or looked at circuits (probably 20+ years since high school and college physics.) I'd like to think I know how they work, but something isn't ...
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1 vote
1 answer
165 views

What is wrong with my circuit and how can I fix it?

This circuit used to work before I soldered it. When I initially soldered it, I used a 6V battery and it was oscillating, but the speaker was very quiet. I went with a 9V battery and I re-soldered ...
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4 votes
2 answers
262 views

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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0 votes
0 answers
52 views

Very high current frequency on transistor collector

simulate this circuit – Schematic created using CircuitLab I am designing astable multivibrator for homework and I have calculated values for resistors and capacitors (hopefully right) but I ...
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3 votes
2 answers
557 views

Astable multivibrator using op amps - why does it start?

I'm new to electronics and I'm learning some circuits with op amps. Now I have been shown this astable multivibrator. I understand how it works. The op amp is saturated at one side or the other ...
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0 votes
0 answers
59 views

Toggling between astable and monostable input to dual 555 timer pulse generator

Hi there, I am looking to build a simple analog circuit to generate adjustable pulses for a medical device. The current circuit utilises 2x LMC555 timers - one in an astable configuration to generate ...
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0 votes
1 answer
402 views

555 timer to measure variable capacitance

I've no experience with complicated circuits. Currently thinking about a simple circuit for detecting a variable capacitance, e.g for liquid level or moisture sensing. I came across the 555 timer ...
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  • 5
0 votes
2 answers
154 views

555 timer Theremin - capacitor choice, and question about mixing signals

I'm trying to create 555-timer based Theremin, but I have a few questions that I don't quite understand. For now, I'm building it on a breadboard (yes, I know it's not the best option), but I don't ...
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1 vote
2 answers
228 views

NE555 - astable flashing alternative LED circuit

NE 555 help - astable alternate flashing LED circuit "In the circuit, the LED1 lights when the output pin has a HIGH state and LED2 lights when the output is in a LOW state." - I couldn't ...
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0 votes
1 answer
74 views

What would be the main advantages of constructing an astable multivibrator with two CMOS inverters?

What would be the main advantages of constructing an astable multivibrator with two CMOS inverters? Can these semiconductor devices be declared to introduce small parasitic capacitances to the circuit?...
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0 votes
0 answers
194 views

Circuit question for LM358 and NE555

I have made an IR proximity sensor which works fine when an LED is connected. Figure 1: This is the IR receiver and emitter part of the circuit. The white LED is connected to ground via a 270 ohm ...
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3 votes
1 answer
397 views

Astable multivibrator: what starts the first cycle

I think I understand how the astable multivibrator works once the LEDs are blinking (cf. below), but I don't understand how the first cycle begins. I can see that at first, the 2 LEDs are on (based ...
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0 answers
57 views

555 Timer Astable Mode

Just to clear things up. This is NOT a homework question, but it is lecture notes used as a practice exam. I am trying to understand the 555 timer in oscillation (Astable) mode particularly the ...
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  • 180
2 votes
1 answer
96 views

I'd like to know whether my attempt to increase duty cycle will work

I've been looking for a solution to make an astable multivibrator give me a 90% duty cycle or a duty cycle above 50%. This is what I came up with. I have very limited resources and means of testing, ...
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0 votes
0 answers
86 views

I've built dead bug (on steroids) boost converter

I know it looks sloppy but this is my very own homemade boost converter! It outputs 6watts of power from a 3.7v battery(phone battery)... It's switched by an astable multivibrator, and the switch is ...
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2 votes
2 answers
743 views

Bypass capacitor in 555ic

What will happen if we don't bypass capacitor at pin 5 of 555 ic as an astable multivibrator.Will voltage/current changes in line affect on pulse width?will capacitor at pin 1 discharge late?
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0 votes
0 answers
48 views

How does a boost converter power the oscillating circuit and load at the same time?

so I've put together a boost converter circuit of my own and I have a problem, I want my boost converter to output reasonably high current but whenever I connect a high current load - the astable ...
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9 votes
4 answers
8k views

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 ...
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  • 101
0 votes
1 answer
56 views

CMOS astable circuit

I have made the following astable circuit in Multisim: However, it didn't work (oscilloscope reads 0V as an output.) I think the problem is because of VDD and GND pins which are hidden in Multisim. ...
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0 votes
1 answer
138 views

Feedback on astable 555 timer circuit to control MAC valve for turbo control

I have some questions and wanted to get feedback on this circuit I have put together. Basically to see if there is something I missed or obvious that I should change or should have designed ...
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0 votes
1 answer
203 views

Two questions about astable multivibrators and transformers

Here's something that confuses me: The output on an astable multivibrator will be shown on a multimeter as half the input voltage (for example we have 9V-0V-9V-0V...and the multimeter averages it out ...
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-1 votes
2 answers
248 views

Gating an astable 555 output signal in a way that oscilation always starts with a Low to High transition

simply, the circuit is a 38KHz signal generator for an IR remote project. the output signal should be gated by an MCU according to IR timing intervals recorded earlier. the design with the 4148 diode ...
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22 votes
5 answers
2k views

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 ...
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  • 223
3 votes
1 answer
320 views

555 timer that does not output low when reset

I'm trying to design a circuit with the following goals: When not active, output can be either Vcc or floating When triggered by pressing a button, output pulses several times to GND at some ...
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1 vote
2 answers
348 views

Astable multivibrator not working

I was wondering if you can help me to know why my circuit is not working. I have tried with different pre-existing circuit values to make sure the circuit was working properly before I put my ...
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  • 11
1 vote
0 answers
141 views

Astable multivibrator inverter

I'm new to electronics and trying to make an astable multivibrator oscillator. The PSpice simulation doesn't work (it says netlist error when I place a mosfet or a diode) and I get a really low ...
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1 vote
2 answers
59 views

Explain how this astable chain(?) circuit works

The circuit below fades on and off a cascading series of leds in an alternating fashion. I tried reproducing it on a breadboard with 5 leds to try to understand it how it works, and got all sorts of ...
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  • 145
2 votes
2 answers
820 views

BJT astable multivibrator generate triangle wave

In this circuit there is a bjt astable multivibrator. It generates a square wave. And according to the description, at the output of the opamp it generates a triangle wave from this square wave. I've ...
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  • 299
1 vote
1 answer
86 views

Op-Amp Astable Multivibrator - Effect of bypass Switch

For your consideration, I have this Astable-multivibrator via a classic Op-Amp Schmitt Trigger delivering a square signal (here 1.82Hz). I am fine with the circuit with SW1 open as C2 is basically in ...
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0 votes
1 answer
62 views

Electric astable circuit not working

For school I have to build a astable circuit that stays on for 5 seconds and then turns off for 1 second. However my circuit isn't working I am do not know why here is my circuit on a bread board. The ...
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  • 139
7 votes
3 answers
1k views

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 ...
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0 votes
1 answer
1k views

What is the purpose of higher-resistance resistors in Astable Multivibrator circuit?

The astable multivibrator circuit has two higher-resistance resistors (47k on the pic). What are they there for? Wouldn't it work without? And what is exactly their function? I spent a lot of time ...
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0 votes
1 answer
117 views

Why does the first pulse have a different duration than the other pulses?

Why does the triggered astable in the next figure have the duration of the logical component "0" of the first pulse lasting 2 times the logical component "0" duration of the next pulses (see the ...
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0 votes
1 answer
238 views

555 timer giving unexpected output (astable multivibrator)

I am using this design: The only exception that C2 is 150nF to change the timing slightly. When I plug in the circuit and attach an LED across GND and pin 3 output the LED is static on. However, on ...
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