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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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6answers
736 views

Where do overtones in a 555 generated square wave come from?

I have built a 555 oscillator and connected it to a speaker. Using an oscilloscope I adjusted the 555 to generate a 2.5kHz square wave. I then held a microphone up to the speaker and fed the input ...
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2answers
50 views

Getting trigger signal for 555 timer from elevator button

I want to turn a load like light on for a certain time when one of elevator buttons pressed say button 1 and while the button pressed the load should be on. In the figure below circuit 1 describe how ...
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2answers
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555 PWM motor driver controlled by external analog signal

I used the below 555 timer PWM circuit to control the speed of a dc motor, and it works like a charm :) now i have a requirement to change the PWM speed externally from another module, that module ...
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2answers
58 views

2-Bit timer with 1 ms period

I am trying to find a simple hardware solution to implement a 2-bit timer that gives out 2-bits continuously repeating data 00, 01, 10, 11, 00, 01.... whose time period is approx 1ms. The accuracy and ...
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1answer
45 views

Why should we charge the capacitor halfway in 555 timer circuit(as given in datasheet)?

In the Texas Instruments datasheet for LM555 IC, at Page 11 below Figure 15, the calculations for charging and discharging of the capacitor are given. In those calculations, the capacitor is made to ...
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1answer
41 views

Cascade of 555 timer with Control Voltage not triggering

Hi I'm currently working on a cascade 555 circuit, both operating in the monostable mode. I also want to be able to control the pulse width with a voltage so am using applying 0-5v to the ctrl pin (...
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2answers
58 views

555 Timer - How to quickly discharge RC capacitor

I'm using a 555 timer to turn off an LED with delay. Here is the circuit. All I want to implement is, to get the input voltage changes in output with a constant delay. When I close the switch, the ...
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1answer
42 views

Capacitor Discharge Pin 7 555 Timer

I am very new to electric engineering, so bear with me ;) Before building the circuit IRL, I wanted to try to build a simple 555 timer with a simulator following ...
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1answer
101 views

555 timer to drive transistors with low load resistance

Recently, I have a project that needs to heat up a metal filament with a single pulse voltage. I built a circuit with 555 timer and transistors to heat up the metal filament(0.2 ohm). The circuit ...
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1answer
35 views

Using a CMOS 555 as a window comparator

I've been working on a small project inspired by this question that uses a CMOS 555 timer as a power button controller (short press to turn on, 3s hold to turn off), the goal being to design a ...
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1answer
44 views

Power-on delay with 555 Timer

I am trying to create a power-on delay with a 555 timer IC. I have never used one of these before and I am finding it a bit tricky to make applications with it - a lot going on. I found this circuit ...
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0answers
52 views

Any improvements you can suggest, to these two 555 circuits? [duplicate]

This is a continuation of my original question that got put on hold... Any IC, to control a LED with a single push-button (ON,OFF,FLASH) I have come up with two solutions that work for me: a push ...
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3answers
101 views

Rapidly driving a keyboard signal

My goal is to build something that simulates rapidity (50 to 1k Hz) pressing a key on a USB keyboard. My first inclination was drive a transistor from a 555 timer with the two keyboard matrix pins on ...
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2answers
65 views

7555 monostable timer not resetting

I'm using a 7555 timer in monostable configuration to control a load of about 1A. If I disconnect the 1A load or use a bench supply it works fine, but the drop in voltage from the batteries seems to ...
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1answer
95 views

What is 0.693, and 1.1, and 1.44 in IC 555 Calculations

I tried a lot to figure out but could not find any answer to this question anywhere. For calculating pulse width in a standard IC 555 astable and monostable configurations we use the following ...
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2answers
96 views

Designing a 555 led blinker [closed]

Found a nice guide on how to make a led turning signal for bikes based the 555 timer which contained this schematic: But no matter how I do it, I cannot make it work.The leds won't blink.... What's ...
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2answers
49 views

Trigger based on Time Difference between two sensors / Catch a Miss on sensor

I have two Sensors S1 and S2, S1 is a 24v inductive proximity sensor which i isolated using octocoupler to work at 5v and S2 is a transmissive type phototransistor sensor, both are placed at a fixed ...
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3answers
78 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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0answers
49 views

LMC555 Fading led problem

I'am developing a simple badge with a fading led. My idea was a LMC555 timer powered by a cr1025 battery, these batteries have a nominal voltage of 3v. I chose the LMC555 for its low operating voltage....
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2answers
85 views

Why would you loop 'Out' back to 'Vcc'?

I do not understand the NE556 circuit depicted in this data sheet: https://cdn-reichelt.de/documents/datenblatt/A200/NE-SA-SE556-TI.pdf on page 6 in figure 1. More specifically I do not understand ...
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4answers
2k views

Super Duper Vdd stiffening required on 555 timer, what is the best way?

I am using a 555 timer for a (16bit) frequency sensor/counter. It works by counting the number of pulses read in the 125ms sample time set by a 555 timer; resets & repeats... I am using the ...
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0answers
67 views

Lower amps than expected?

I build an inverter to power some panels of EL paint (If you don't know what EL paint is check out this link). It puts out some very high voltage and I thought I'd check to see what amperage it is ...
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0answers
44 views

555 Monostable delay circuit misbehaving

I have designed a basic application of a 555 in a monostable configuration to delay the LOW/off state of an output signal. (The output drives some power electronics through an optocoupler). As per my ...
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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 ...
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1answer
71 views

Multiple NE555 timers, disable retriggering until all have finished

I plan to build a small timer device that, when triggered, lights up 3 leds. After 30 min, the first goes dark, after another 30 min the second and yet another 30 min later the third. It's pretty ...
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1answer
48 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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0answers
32 views

Simulation behaves differently in Proteus vs Icircuit

I'm an electrical engineer student and I'm trying to make an LED Flasher circuit using a 555 Timer. When I simulated the circuit in Proteus simulator, it's not working! But in Icircuit simulator it ...
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1answer
88 views

Differences between LM555CN-R and LM555CN/NOPB

I am trying to buy a LM555CN-R online, however I can only find an LM555CN/NOPB. What are the differences, if any, on these chips?
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2answers
30 views

Suitable protection for elements on power line

I am working on mini project with 555 timer. The LED diode is not a diode, but a 12V LED string. What happens if there is a sudden drop in voltage? Motor will induce voltage of opposite polarity. The ...
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0answers
76 views

Astable 555 used for AC to DC Halfwave to DC stable conversion, is what I have done correct?

I have this falstad-circuit: And here it is per request, as a SCH file screen: I'm trying to use a 555 astable to convert a variable AC with maximum of 12V (coming from Bicycle Hub) to 8VDC, ...
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2answers
106 views

Timer Protection Circuit

I need to create a circuit that sends out a signal only if the input it on for longer than a specified time. Lets say 20 seconds for this example. So if the input to the circuit was pulled high for 10 ...
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2answers
58 views

555 IC Astable Mode - Does the voltage generally affect the frequency?

Sorry if it's been asked before, I'm asking to satisfy a curiosity. I'm new to electronics, and I'm messing around with the perennial 555 IC. I've been introduced to the following formula which allows ...
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1answer
87 views

NE555 power controller not working with big motors

simulate this circuit – Schematic created using CircuitLab Backstory: Ok, so I thought that a making a PWM controller would be a fun weekend project, it's been a week now and I still can't ...
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1answer
75 views

555 timer only works when I disconnect pin 4 from V+ and touch the jumper

I set up a pulse circuit on a breadboard with a 555 timer. Input voltage is 5 V. My values are roughly: C = 100nf R1 = 1K R2 = 1M I'm using this schematic: (Source: https://www.allaboutcircuits....
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6answers
587 views

Why can't my 555-based DC-DC boost converter supply even 3 milliamps at 12V?

I hope someone can help me. I've been tearing my hair out for the past couple of weeks trying to make a simple DC-DC boost circuit. It puts out a nice 12-ish volts when not loaded, but as soon as I ...
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1answer
71 views

Simulated 555 timer not working

https://www.tinkercad.com/things/2CN1eOTbmTe I am a beginner in electronics. I've been trying to make an astable 555 Timer in TinkerCAD as an oscillator for my own project of making a clock, without ...
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1answer
144 views

Why does this Mosfet get Hot?

I have an IRF740 mosfet that doesn't get hot in one circuit but then gets completely hot in another identical circuit and for the life of me can not figure out why. Well the circuits aren't exactly ...
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0answers
51 views

CircuitLab simulation of 555 timer - OUT HIGH always delivering 5V irrespective of Vcc?

I've scratched together a design for a 555 timer based driver for an IR540 MOSFET. But in CircuitLab the simulator shows the 555's OUT voltage is always 5V when high, for Vcc ranges 3.3V through 24V. ...
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0answers
62 views

555 circuit acting weirdly

In essense, whatI have are four 555s (2x556) One is a 0.5 s monostable,the other a 147 Hz tone generator. The other is a (30 s) monostable, and a 0.3 s astable. If I run the 0.3 s astable on its own, ...
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1answer
78 views

Why does this 555 timer not work correctly when I plug in the Z80 CPU ground?

I am trying to build this circuit here: https://www.youtube.com/watch?v=AZb4NLXx1aM But instead of using the same timer setup I am using this: When I connect the ground pin of the CPU, the LED ...
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1answer
100 views

555 square wave generation with frequency feedback

Knowing that 555's behaviour varies according to temperature, I wondered: In an astable configuration, is there some way to measure output frequency, compare it with some desired value, and use this ...
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2answers
28 views

555 Timer with controllable reset

I have a 555 monostable set up which is triggered when an output from another circuit goes low. This then remains on for 10s. This all works almost perfectly. My issue is that when the output from ...
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2answers
61 views

How to make a circuit to pulse an output when a momentary switch is released

I need to make a circuit that has a momentary switch and a light (30mW). When the switch is pressed, nothing should happen, but when the switch is released, I want it to pulse the light for a short ...
0
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1answer
51 views

Enterprise model blinkers - two fast flashes and pause for 3s and repeat LED circuit (with 555 and/or 556 and/or 4017) [closed]

I'm building a Revell Enterprise Into Darkness model with LEDs and I need help with circuit that makes two fast flashes, pauses for 3 seconds, then repeats. as seen in the movie. I have searched and ...
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1answer
75 views

Voltage doubler using 555 timer

I found this circuit, a voltage doubler with 555. The duty cycle of the 555 is 50%. Does changing the duty cycle of the 555 timer affect the voltage output like in boost converter? Or does it not ...
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1answer
256 views

555 timer delay circuit + light sensor?

I am quite new to electronics and I would like to combine these 2 circuits together so that during complete darkness on the LDR, the LED would turn on instantly and when light falls on the LDR there ...
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1answer
52 views

Help using a 555 timer to increment counter that needs to be pulled low

I need a little help with a project. I'm very new to building circuits. I have this NE555 duty-cycle pulse frequency adjustable square wave generator module, which I have connected to a 12V DC source. ...
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2answers
117 views

Pull up resistor for 555 Timer IC

https://makezine.com/projects/laser-tripwire-alarm/ I need help determining the pull up resistor needed for this circuit. It uses a 555 Timer IC. The resistor R1 acts as a pull-up resistor for pin ...
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3answers
112 views

Is it possible to get complementary clock output from a clock generator such as a 555 timer using simple digital logic?

I'd like to get complementary output from a 555 timer. I've seen previous suggestions of using a D Flip Flop, which is a fine suggestion, however that halves the frequency at the outputs of the flip ...
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0answers
24 views

How is trigger initially higher than vcc/3 in 555 monostable timer?

I get that the trigger must be lower than vcc/3 in order for the comparator to show '1'. But initially how is the trigger higher than vcc/3? In some text it says trigger is initially vcc and so ...