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Role of the load resistors in an astable multivibrator

I am currently trying to wrap my head around astable multivibrators. I want to design a circuit that oscilates at about 1 kHz. The formula I am using to determine the values for the base resistors (I ...
balu's user avatar
  • 55
1 vote
1 answer
76 views

Modified astable multivibrator with sharp edges

I am designing an astable multivibrator that would avoid rounded output edges and also has a totem pole output, so it is able to drive a small charge pump. So I decided to replace a collector ...
Michal Podmanický's user avatar
0 votes
3 answers
187 views

How to get megahertz frequency with a 555?

I need to produce a 1.7 MHz signal. Up to around 200 kHz the 555 IC and my simple astable circuit are working just fine as expected, but when I decrease R1 and R2 to less than 100 Ω the frequency ...
Vahid Heidary's user avatar
5 votes
2 answers
179 views

What is this extra diode (LED) between the bases of transistors in an astable multivibrator?

Can someone explain what this extra LED between the bases of the transistors in an astable multivibrator does? I built the prototype and I see that without this LED there is no blinking. Both sides of ...
Evg's user avatar
  • 51
0 votes
2 answers
133 views

How does a capacitor in an astable multivibrator turn off a BJT?

I've recently started learning about astable multivibrators. I understand that the capacitors in a circuit like the one below create the alternating current by charging up one at a time, and once they ...
EskimoJones's user avatar
3 votes
1 answer
313 views

Unable to get my astable multi-vibrator working in LTspice

I'm trying to build a basic square wave oscillator using an astable vibrator made with an op-amp for my Intro to Circuits class. Unfortunately, I cannot get LTspice to simulate the oscillations. I've ...
Jgely's user avatar
  • 33
2 votes
2 answers
268 views

555 Timer Astable Multivibrator Circuit Analysis

I was looking at a dead Molex "Suitcase" terminal applicators and found on its controller board this 555 circuit. It appears to be an astable multivibrator, but not the typical kind. It ...
Erik Vincent's user avatar
1 vote
1 answer
102 views

Measuring capacitance with NE555 in astable mode

I have one problem with my project. I trying to measure capacitance with NE555, but i have problem with protection. In this schemeatic instead of a capacitor, I have put connection socket 01x02 for ...
Византија Исток's user avatar
2 votes
7 answers
602 views

Regulating output of 555 astable oscillator [duplicate]

I need to build a circuit that takes a 12v DC input and produces a 5v DC 30Hz square wave. My thinking is to produce the square wave using a 555 in an astable oscillator configuration, and then step ...
Andrew C's user avatar
4 votes
2 answers
147 views

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 ...
Frank's user avatar
  • 143
1 vote
1 answer
169 views

Square, Triangular and Sinusoidal Wave Generator with AmpOp and Diodes

I'm having trouble building a circuit to generate square, triangular, and sine waves. In theory (calculations), everything is correct, and in the simulation (done in LTSpice) everything is also ...
benjamin_ee's user avatar
0 votes
1 answer
155 views

Astable multivibrator 555 circuit not working

I'm a beginner in electronics. I'm trying to follow the below schematic for building an astable 555 circuit. Based on the resistance set on the trimmer potentiometer, the speaker should make sounds of ...
slazien's user avatar
0 votes
1 answer
41 views

What is the effect of V+ given from bottom in this multivibrator?

In the astable multi vibrator, the second figure has a V+ voltage given additionally. What is the output of that circuit digram compared to first figure?
O-Negative's user avatar
3 votes
3 answers
170 views

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. ...
user18926955's user avatar
0 votes
0 answers
111 views

Which complementary astable multivibrator is more reliable to produce for tests on a breadboard?

Astable multivibrator coupled with complementary astable multivibrator: I tried to build this schematic on a breadboard, but the complementary astable multivibrator circuit on the right does not work ...
ankyxia06's user avatar
3 votes
3 answers
239 views

Complementary astable multivibrator vibration/oscillation reason

I set up this astable multivibrator on a breadboard. Sometimes it works and flashes on and off it, and sometimes it does not flash on and off - the LED stays on. Is there any reason or specific ...
ankyxia06's user avatar
2 votes
2 answers
162 views

555 timer is unstable for a few seconds after power application

I have built the circuit from this answer. I have R1 = 10k and C1 = 6.8nF which seems to be giving me about 7.5kHz output. The timer works just fine but from a cold startup, the output is wildly ...
brenzo's user avatar
  • 433
0 votes
2 answers
150 views

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 ...
user488476's user avatar
1 vote
4 answers
399 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 ...
lidorov19's user avatar
3 votes
4 answers
843 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 ...
denizyildiz70's user avatar
1 vote
5 answers
728 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 ...
Charlie's user avatar
  • 71
6 votes
2 answers
759 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 ...
Strayed101's user avatar
4 votes
4 answers
1k 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 ...
Bastien's user avatar
  • 144
-3 votes
1 answer
391 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 ...
Abd Alhaleem Bakkor's user avatar
2 votes
1 answer
497 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 ...
PowerTb321's user avatar
0 votes
2 answers
401 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 ...
PowerTb321's user avatar
2 votes
3 answers
456 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 ...
matth's user avatar
  • 127
0 votes
4 answers
425 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 ...
Fela Maslen's user avatar
1 vote
2 answers
331 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 ...
electrovolt's user avatar
0 votes
2 answers
572 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 ...
Abhinav Tahlani's user avatar
0 votes
2 answers
529 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 ...
Abhinav Tahlani's user avatar
1 vote
1 answer
453 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 ...
Abhinav Tahlani's user avatar
2 votes
4 answers
680 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 ...
FZs's user avatar
  • 143
1 vote
2 answers
1k 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 ...
Mike Felts's user avatar
1 vote
1 answer
189 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 ...
sakbaloch's user avatar
4 votes
2 answers
446 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 ...
Anjali Kadambi's user avatar
0 votes
0 answers
62 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 ...
Imigrant159's user avatar
3 votes
2 answers
955 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 ...
Joaquin Brandan's user avatar
0 votes
0 answers
66 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 ...
Alex Mitton's user avatar
0 votes
1 answer
1k 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 ...
JoS's user avatar
  • 5
0 votes
2 answers
292 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 ...
user12940963's user avatar
1 vote
2 answers
700 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 ...
swagdevotee008's user avatar
0 votes
1 answer
84 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?...
ambition's user avatar
0 votes
0 answers
689 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 ...
swagdevotee008's user avatar
3 votes
1 answer
668 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 ...
MagTun's user avatar
  • 251
0 votes
1 answer
117 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 ...
Aaron's user avatar
  • 311
2 votes
1 answer
104 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, ...
Bongani Khumalo's user avatar
0 votes
0 answers
95 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 ...
Bongani Khumalo's user avatar
2 votes
2 answers
1k 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?
M ilyas dhebar's user avatar
0 votes
0 answers
53 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 ...
Bongani Khumalo's user avatar