# Tagged Questions

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. The part is still in widespread use, thanks to its ease of use, low price and good stability. The 556 timer is simply two 555 timers in a single package.

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### 5V to the discharge pin, threshold pin and trigger pin

What happens if I give 5V to the discharge pin, threshold pin and trigger pin of 555 without giving power at pin 8 and grounding at pin 1?
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### How the transistor works in this 555 circuit?

555 Is not able to provide long timing due to its leakage current. The following circuit is very useful to build a long time timer such as 1 hour or more. The accuracy of the time is not important ...
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### 555 Maximum Duration of Output

One more short question on 555. I am required to say what is the maximum possible duration of the output pulse (or signal). I looked it up online (including the datasheet for 555), but found no such ...
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### 555 timer explanation

I have a short question. I have to read this text regarding the 555 IC: LINK As you can see, there is the following sentence: "Even at 5V, the 555 will easily drive LED's and small relays." Can ...
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### 74HC595 LED sign [closed]

I'm new to electronics so I'm sorry if this sounds stupid. I recently created an LED sign consisting of 97 LED's on a piece of wood that all light up at the same time when I supply it with 3v. I have ...
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### What causes inaccurate time in 555?

I would like to use 555 with a relay to make a reliable control circuit. I use 555 as mono-stable and the following equation does not work: t = 1.1*R*C seconds R = 51 K ohm C= 220 uF The ...
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### Should a 555 IC remain powered when a [battery powered] device is turned off?

I'm fairly new to electronics. I wasn't able to find anything addressing this on the Web but that may be because I don't know the search terms to use. I'm trying to design a device that contains two ...
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### Anyway to avoid the startup delay on square wave generator (e.g. 555 astable) circuit?

In the classic 555 astable circuit the external capacitor charges to 2/3 of the Vcc (through R1 and R2) and then is discharged to 1/3 of Vcc (through R2) and then it continues to oscillate between 1/3 ...
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### 555 timer bistable circuit problem: default flip-flop state is 'ON' on power reset

The following circuit is a controller for a water pump. It turns the pump on when the reservoir water level drops below the 'L' probe and turns it off when the level reaches the 'H' probe. This ...
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### Knock Sensor using 555 Timer with a timed light

I have seen a few Knock Sensors using the Piezo Speaker and the Arduino. I am wondering if there is a way to eliminate the Arduino and utilize a 555 Timer and other simpler components so that when the ...
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### 555 and transistors: using a transistor to ground the reset pin of a 555 and how to drive a MOSFET with a 555

Parachute Deployment Timer I am busy trying to build a parachute deployment timer for an amateur rocket using 555 ics What have I done thus far I have a switch that closes temporarily while the ...
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### What type of 555 timer circuit is this [closed]

Could someone please describe what sort of 555 setup/circuit is in the image and how it operates. This is the webpage on which I found it http://www.thefintels.com/aer/protected/timer.htm Thank you ...
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### 555 timer with output voltage equal to 5V?

I am (still) learning about electronic and want to get a 555 timer. From a datasheet (page 5) it looks like when the input voltage is 5V, then the output voltage is only 3.3V. Is that correct? If ...
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### How do I get output impedence of ICs?

I am teaching electronics a few people as a hobby. I wanted to show them that as the frequency increases output voltage of low pass filter(simple first order RC filter) decreases. I don't have a ...
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### Proper Capacitor for 555 Circuit with Simple NPN Amplifier

As I understand it, in the classic 555 with a speaker circuit, the capacitor that is in series with the speaker is there to prevent DC from flowing through the speaker: And this capacitor, C1, is ...
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### 555 circuit confusion

Here is block diagram of 555 timer: I wouldn't analyse it, but under some circumstances (for some voltages at THRESH and TRIG pins), complemented output Q will be at high voltage level, with ...
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### 3*3*3 LED Cube using 555 timer and 4020

Hello everyone I am new to electronics and I am building a LED cube for my class project. The circuit i built was the one i found online and I got it working but i want to add a n-channel mosfet to ...
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### Light intensity control

The circuit is used to control the bank of LEDs using PWM, my problem is the value of R3 is wrong, now I used 10M ohm and it started switching on and off bt the LEDs dont shine bright which means the ...
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### How to balance between frequency and duty cycle in this circuit?

I have this astable circuit that generate square waves with independent control of frequency and duty cycle: For this circuit: $$t_H=0.759\,C\,(R_f+R_y)$$ $$t_L=0.759\,C\,R_x$$ period = 0.759\,...
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### Speed and direction control of motor by using IR & 555 on Proteus. (Circuit with errors is attached.)

I am trying to control motor direction & speed by using IR and 555 on Proteus. Circuit and errors images are attached. Please help me solving this quagmire.
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### Why I am seeing a spike of 9V on output and capacitor in 555 timer

I would like to have high voltage at output initially for a period of time, then low and high ... . But in the following circuit, I see spikes on output (green) and capacitor (blue) for a short period ...
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### Closing a switch for a fixed (but short! milliseconds) amount of time

I would like to create a circuit with a button. When this button is pressed, a circuit should be closed for a fixed amount of time. Right now, I have managed to get the desired effect using an arduino,...
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### How to change the frequency of this sawtooth generator circuit?

I've found the circuit below in "The Art of Electronics" book. This circuit generates sawtooth signal. This is some of what is written about it: By using a current source to charge the timing ...
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### Servo control with 555 timer

first of all this is for an assignment so I have certain limitations, mainly cost. The problem I'm having is I have run out of PWM inputs on my ATtiny45 but I still want to drive a servo. The two PWM ...
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### 555 ticks at different frequency than calculated

I'm trying to get a 250kHz signal with 58% duty cycle from an NE555, i'm using values calculated by an online calculator but the circuit clocks at 168kHz when viewed in an oscilloscope. I'm feeding ...
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I have built a multivibrator oscillator using an op amp circuit (similar to a 555 timer approach) in PSPICE. The output is correct so the entire circuit is functionally working. I am trying to see ...
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### (schematic) Using a micro controller to drive Opto-coupler > 555 timer > MOSFET

I'm trying to use a micro-controller to activate an opto-coupler connected to 555 timer which is connected to a MOSFET. The circuit will drive a solenoid which draws 2amps at 12v. I'm new to circuit ...
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### 555-timer circuit supposed to give 50% duty cycle square wave doesn't

I wanted to build a circuit that gives 50%-duty-cycle square wave. I built the circuit of figure 4.4.6 from this link which is shown below: I used the NE555 chip, and used a potentiometer instead ...
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### How can you wire a 555 timer to gradually decrease sound volume?

Say you are taking in an audio input from a headphone speaker and you would like the audio to gradually decrease until inaudible. Are there better, also very common chips that can do this more ...
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### Automatic and manual clock managing. Errors with ring counter but not with 4-bit counter

I'm building an 8 bit computer and I've just developed the clock. I used a NE555 (datasheet) with some other integrated (74 series) to manage it. The operator could stop signal from 555 (with a ...
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### How to build a circuit that generates a sine wave?

How can I build a circuit to generate sine waves? What I am working on is building a 555-timer circuit that gives 50% duty cycle square wave, then using a low-pass or band-pass filter tuned to the ...
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### Power calculation of circuits

Please read on..... this looks long but is entry level and easy I have done many simple projects based on microcontrollers but have not considered power and required current(for circuit to work) ...
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### Glowing two leds alternatively in a given ratio of time

I want to design a circuit for glowing two leds for alternate intervals for different input voltages. For example: Consider two LEDS Red and Green. When the input voltage to the circuit is 0-5Volts ...
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### 555 autostart counting

In a monostable configuration of the 555: http://circuitdigest.com/electronic-circuits/555-timer-monostable-circuit-diagram I have connected pin2 to the ground all the time. My goal is that once the ...
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### TIP 120 replacement

Although I read the article advising against using TIP120: http://sensitiveresearch.com/DoNotTIP/ I only have couple of other transistors on my hand: ...
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### 555 timer digital clock

How would you go about connecting a 555 timer to a circuit with a 16x2 LCD display, which is already connected, to create a digital clock that counts the time? Do you have a sample of how this code ...
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### 555 delay circuit is unsatble

Hello I have built the 555 delay power off circuit by using these 2 guides: home.cogeco.ca/~rpaisley4/LM555.html#30 http://www.electroschematics.com/5963/adjustable-timer-1-10-minute/ I using a ...
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### H Bridge 555 Timer Votlage Drop

I am building the circuit presented at 4:45 in this video https://www.youtube.com/watch?v=iYafyPZ15g8 The problem is the frequency of the output of the 555 timer changes depending on the whipper but ...
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### 555 VCO Circuit - Speaker to VCC?

Hello! I have a simple question concerning this circuit I have built: It is a 555 Voltage Controlled Oscillator I have built as a foundation for my signal generator circuit. The circuit works great,...
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### make motor ON and OFF for fixed interval of time

I am new to electronic, studied this subject long time back but now not able to recall anything out of it. I have requirement to ON the motor after fix interval of 4 hours and run it for 30 seconds ...
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### What circuit should I study, to learn all the details of the 555 timer? [closed]

I understand OHM's Law, and have a conceptual grasp of RCL circuits, but am a little weak on the math. I am good at math, even a little calculus, just weak on RCL math. I am trying to understand the ...
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### Variable Resistance

simulate this circuit – Schematic created using CircuitLab This is a pulse generator, outputting square pulses with about 8% duty cycle. Tuning R2 down to 120k will result in the same high time,...
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### How does the internal circuit of the 555 works in terms of transistors

I saw many explanations of 555 internal design based on block diagrams. It's good for basic understanding, but I want to understand how those internal transistor circuits make those blocks. I can see (...
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### I need some help calculating values for a variable 555 oscillator circuit

For the past few hours i have been strugling with a 555 timer. What i am trying to do is generate a square wave of variable frequency controlled by a potentiometer. At the time i have a 200KΩ ...
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### Ultra low power 555 timer circuit

I am trying to design a circuit involving an LMC555 CMOS timer operating as a monostable multivibrator. Essentially, I want a momentary switch to turn on a set of LEDs for ~20 seconds and then turn ...
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### Timer sequence with delayed off and long trigger pulse

Attached here below is the input and out put sequence that I am trying to achieve with a timing circuit. This looks like something that might be achieved with a few monostable 555 timers, but I am ...
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### 555 monostable/astable on one chip

Is there any way to use a single 555 chip which could be switched with a two-state switch between monostable mode (one-shot pulse of a certain width) and astable (continuous pulses of a certain width)?...
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### Complicated photo-motion-timer switch design?

Here's my scenario: I have an array of 120V LED fixtures that need to be turned on for 10 minutes when the following conditions occur: It's dark out AND Someone walks in front of a motion sensor ...