Questions tagged [astable]
The astable tag has no usage guidance.
106
questions
6
votes
2answers
675 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 ...
4
votes
4answers
532 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 ...
-3
votes
1answer
86 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 ...
2
votes
1answer
230 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 ...
0
votes
2answers
72 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 ...
2
votes
3answers
91 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 ...
0
votes
4answers
136 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 ...
1
vote
2answers
92 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 ...
0
votes
2answers
83 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 ...
0
votes
2answers
78 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 ...
1
vote
1answer
76 views
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 ...
2
votes
4answers
208 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 ...
0
votes
2answers
211 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 ...
1
vote
1answer
150 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 ...
4
votes
2answers
213 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 ...
0
votes
0answers
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 ...
3
votes
2answers
451 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
...
0
votes
0answers
56 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 ...
0
votes
1answer
245 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 ...
0
votes
2answers
121 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 ...
1
vote
2answers
141 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 ...
0
votes
1answer
71 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?...
0
votes
0answers
137 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 ...
3
votes
1answer
340 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 ...
0
votes
0answers
52 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 ...
2
votes
1answer
95 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, ...
0
votes
0answers
80 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 ...
2
votes
2answers
667 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?
0
votes
0answers
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 ...
9
votes
4answers
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 ...
0
votes
1answer
52 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.
...
0
votes
1answer
115 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 ...
0
votes
1answer
181 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 ...
-1
votes
2answers
221 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 ...
22
votes
5answers
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 ...
3
votes
1answer
285 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 ...
1
vote
2answers
250 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 ...
1
vote
0answers
111 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 ...
1
vote
2answers
53 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 ...
2
votes
2answers
703 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 ...
1
vote
1answer
82 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 ...
0
votes
1answer
61 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 ...
7
votes
3answers
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 ...
0
votes
1answer
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 ...
0
votes
1answer
113 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 ...
0
votes
1answer
219 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 ...
2
votes
1answer
1k views
Astable 555 timer circuit that resets on a heartbeat
I'm trying to design a circuit that will reset my ESP8266 when it crashes/hangs. It does this by sending a heartbeat to a 555 timer every minute which resets the 555 timer. The 555 timer is configured ...
5
votes
2answers
330 views
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 ...
1
vote
0answers
68 views
Variable frequency of an astable
I have to make the frequency variable of an square waveform generator built with the help of an astable. I modified a circuit a found on the internet and everything seems good with only one exception: ...
-3
votes
1answer
688 views
Astable 555 not oscillating [closed]
I've been struggling with building a 555 timer for a project. I get the expected voltage at pin 3 (output), but the problem is that it's not oscillating. The Vout is constantly 8.4V, while I expected ...
