Questions tagged [555]

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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555 timer in astable mode: How can I achieve longer low output than high?

I'm attempting to make a simplistic solenoid driver circuit using a standard astable 555 timer configuration with a TIP122 NPN transistor. The problem with the current circuit is that the output is ...
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4answers
724 views

How can I generate a logic pulse from a broken IR beam?

I would like to trigger a [7]555 timer when a phototransistor stops receiving light from an IR led, more precisely when the (expected to be smallish) signal from the light-sensitive voltage divider, ...
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Can someone check over my schematic?

This is the first schematic I have made that was not a simple LED. I want to know if it seems good before I go and build it (and buy the parts). Here is the schematic: Here are a few of my concerns: ...
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Why does 555 timer output change based on load?

I have a 555 timer setup in astable mode, with a frequency of about 1Hz which I measured and verified without load. Out of curiosity, I connected an 8 ohm speaker, expecting not to hear anything. ...
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1answer
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Difference between NE555P and 555CN?

I'm working on a circuit that uses two 555 timers. At the electronics store, they gave me a handful of 555 chips, I only noticed the difference when I finished my circuit: the R1 value is shorted out, ...
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1answer
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How to prevent 555 timer interference

I made a triple PWM motor controller with a 555 timer hooked up to 3 IRF621 MOSFETS to the motors. I am having interference troubles. When I turn one knob up, the other motor wants to change speed a ...
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1answer
401 views

555 trigger frequency signal

So, I'm remembering that back in school, I managed to make a 555 signal create a tone signal, and that another 555 could trigger the 555, such that I had a variable toned signal that could be pulsed. ...
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1answer
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Reset 555 timer when trigger switch is released

I have a simple 5 second Monostable 555 Timer circuit. Trigger Pin (#2) is connected to a momentary push switch. When it is pressed, the timer is started and LED stays on for 5 seconds. What I want ...
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Is there a way to control the PWM duty cycle of a 555 timer without using a variable resistor?

I need to control the duty cycle of a Pulse Width Modulation (PWM) circuit from a DC voltage input. To do this, I've been looking into 555-timer circuits - but every circuit I've come across involves ...
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3answers
823 views

single-capacitor oscillator choice for digital theremin

Intro One of the pupils puzzled me with a question of building a theremin - a basic musical instrument which has a pitch manipulated by moving the hand around the vertical antenna. Due to specifics ...
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What is the output voltage of this 555 timer high voltage circuit?

I'm trying to calculate the theoritical output voltage of the following 555 timer high voltage circuit. It claims to output up to ...
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Functional difference between various astable 555 circuits

Looking through some 555 square-wave-generator circuits (possibly with variable duty cycle for 4-wire PWM fan control) I've found three different circuits: From the Wikipedia 555 article, a "standard ...
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Why won't this 555 timer flashing circuit work?

The circuit which I made shows the following behavior, when power is given to the circuit: Sometimes it lights up, sometimes it doesn't. When it does light up, it flashes properly for a few seconds ...
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196 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 ...
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Circuit for flashing LEDs for airplane model wing, tail and beacon lights using 555 [closed]

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 ...
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Why are 555 IC pin diagrams so random?

I was going to start learning how to use a 555 timer as an oscillator, however am greatly confused in the pin configurations example schematics provide me. To show visually what I mean, A random ...
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Handmade timer versus IC

Are there power consumption benefits between a discrete timer: astable multivibrator or some other; and an integrated circuit? I have a time dependent circuit in a project and I went looking for the ...
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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 of ...
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3answers
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On— off— on— off timer circuit

I want to make a circuit to do something that is relatively simple but I need to find the optimal way to do it in order to take as little current as possible. Here is what I want to do: When a ...
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707 views

Where is the oscillator in the 555 chip provided here?

I have tried a while to understand how the 555 chip is built. I opened the datasheet of TI available here : http://www.ti.com/lit/ds/symlink/lm555.pdf Anyway this is the schematic from the datasheet ...
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Using 555 to generate square signal with fixed duty cycle / variable frequency

I am attempting to design a circuit whose output is a square wave with the following properties: Fixed duty cycle, as high as possible (let's say 99%) Variable frequency, between 0.2 - 20 Hz (I'm ...
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Using microcontroller as oscillator for high voltage power suppy?

MightyOhm has designed a geiger counter which is here. I am not very clear but I think he is using the 555 timer as an oscillator in the high voltage power supply section. I've attached his schematic ...
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745 views

7555 timer replacement

I want to build this circuit but I do not have a 7555 low power timer so wondered if I can use a NE555? Also can I use a 2N2222 trasistor instead of a BC108? I don't want to try and build it without ...
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476 views

Should I expect my power line to be this noisy?

I'm building a circuit that contains a 555 timer wired to operate in monostable mode. In the final project, the trigger to the monostable will be driven at around 60Hz, with the output driving some ...
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Parallel Port - Voltage / Current required for input pin

I am developing a program to send and receive sigal to my circuit and pc. Actually I have to count the pulses or (frequency of high pulse) generated from a 555 timer IC in my circuit. When I connect a ...
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445 views

What's wrong with giving a really long low pulse to a 555 timer?

A number > 0 of 555 timer tutorials warn against holding the trigger of a 555 timer in monostable configuration low for longer than the duration of the output pulse. Why not?
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Producing different types of tones using the 555 timer

I'm learning how to work with the 555 timer (astable mode) and decided to make a simple synth. The sound from a square wave is rather harsh so I'm trying understand how to modify it to make different ...
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LED Blinking with 555 on button press

This may be a simple question, but I couldn't find anything exactly for this. I wish to implement LED blinking if a button is pressed, and it should continue to blink, unless button is pressed again. ...
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1answer
99 views

How to avoid this voltage when I turn on the circuit?

What I want to do is an Delay ON, but when I press the switch this voltage pass for a brief moment and turns the led on for a moment. How can I avoid this? Should I put the switch somewhere else? ...
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555 timer one-shot 30 second light LED strip, TOTALLY CONFUSED!

I'm working on a personal project and I am at my absolute whits end here. I have a configurable N.O. or N.C. switch (nteinc Magnetic Alarm Reed Switch) so I'm not too concerned with which way I use it....
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How can I debug my 555 timer circuit?

I'm trying to build an LED chaser circuit using a 555 timer and a 4017 counter. I've built the circuit successfully on a breadboard, but now that I tried to create a soldered version it just does not ...
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1answer
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Using a 555 instead of 7555

Im creating this circuit and it requires a 7555 timer. A 7555 timer is like the next generation 555 since it is CMOS. Now there are no 7555s or CMOS 555 in my area and was wondering what will happen ...
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General PSpice and 555 timer question regarding precision

I have been experimenting with values recorded using a multimeter versus the voltages (RMS) simulated using capture. I simultaneously setup a circuit using a breadboard and drew exactly the same ...
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292 views

How to use the same switch to control LED and vary resistance?

I am struck with a simple board design problem. The requirements are : I have a 4 position slide switch according to the position of the slide switch, I should turn on different colored LEDs and also ...
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1answer
915 views

What is the diode for in this 555 circuit?

Here is a schematic of a 555 setup to create a single shot voltage sawtooth pulse across the capacitor C2. It also outputs a square wave pulse on pin 3. A (reversed biased) Zener diode is used ...
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421 views

Very weak LED dimming with combined PWM signals using 555 timers

First of all, here's the circuit: What I'm doing here is using 2 PWM signals generated by 555 timers to control the warmth of the LEDs and the brightness. The top 555 is the brightness control and ...
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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/...
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555 fading in&out if possible with pwm & led array

i'm new here and also in the electronics world so pls be patient with my ignorance. I's now months that i'm fascinated by the 555 timer. The stuff you can do with such a tiny thing is impressing. ...
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9k views

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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651 views

Buzzer alarm problem

I've got an assignment to make some kind of alarm. When user presses the push button, 1kHz sound should be generated and outputted on some kind of speaker (I'll use buzzer). That part I know how to ...
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Steering Diodes

What are the "steering diodes" next to the pot for? Source: http://www.youtube.com/watch?v=OXsu29K_Ap4
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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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555 Timer with a 50% duty cycle

I'm trying to build a 555 timer with a 50% duty cycle. I followed the instructions given here (pg 12). I used a 470 microfarad capacitor, 150 ohm resistor and a kohm resistor. The output voltage is ...
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How can I make a linearly tunable 50% duty astable multivibrator?

I want to make an astable multivibrator with a 50% duty cycle that can be tuned with a potentiometer for generating sound, so accuracy is desired. My first thought was to build the standard one with ...
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How to produce digital pulses using 555 timer IC for stepper motor? [closed]

I need to run bipolar stepper motor with 555 timer IC. Is there any simple circuit to produce the pulses to rotate the stepper motor clockwise, anti-clockwise with the desired speed? If there are ...
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260 views

Generation of a shorter pulse based on trigger (similar to 555 as monostable)

I need to create a shorter pulse based on a trigger signal. Trigger signal has a duration between 1 to 10 ms and the desired output should be 0.5 ms. To do the opposite (longer output pulse than ...
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498 views

Cheap and simple solution for low frequency (period about tens of seconds) pulse generator

I need to generate a pulse each let's say 30 seconds. I don't need this period to be any precise (20...40 seconds fluctuation will be OK). The pulse duration should be about 1 ms. I tried to ...
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545 views

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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Floating charge pump for high side N-channel MOSFET bias

This question is derived from this one. I'd like to keep gate on for an indefinite period of time (100% Duty cycle) and for that I'd like to use charge pump since idea with relay is not attractive. ...
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Flyback transformer - ambiguous schematics and other issues

I'm currently using this schematic for a flyback transformer: (source: eleccircuit.com) As you can see, there's a big problem - neither the schematic, nor the website describing it, give the value ...

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