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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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1answer
127 views

LM555 timers for control of a secure door

I will explain existing hardware followed by my desired operation thereof. I have a security door the controller of which has failed. The door has four electronic deadbolts. -- A) Two open ...
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3answers
244 views

555 timer not switching at threshold voltage

This is a 555 timer circuit which is supposed to generate two short pulses, back to back, at a regular frequency. The top 555 is configured as astable to control the frequency. It feeds the first 555 ...
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0answers
48 views

Comparing the results of two electronic dice

I made two electronic circuits each consisting of a 555 Timer, a CD4017 and 7 leds in the shape of what you'd find on a dice. They work great and all, but I want to "compare" the results of both and ...
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1answer
109 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
100 views

Capacitor charging voltage showing ripples on scope. Origin?

I have an RC circuit delivering a square signal via a standard 555 timer set in monostable. I am powering the 555 with 4.88V DC directly from the Arduino, which itself is taking its power from the ...
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1answer
162 views

Latching switch to single pulse circuit? (monostable multivibrator with 555?)

I am looking at using a latching switch (SPDT) to momentarily connect two pins. This is for a power button for a raspberry pi, so to power the machine from a hold state you have to momentarily short ...
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3answers
105 views

555 as slow PWM driver

I would like a slow PWM output, driving a relay turning an AC heating element on and off. I desire a period time of around 10s. What is a realistic upper period time limit for a PWM circuit like the ...
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1answer
22 views

Time step Error In Multisim Using 555 timer

I am trying to simulate a circuit in multisim and I keep running into the following error. (new to multisim) I attached a picture of the circuit and error. Any advice on how to fix this? The purpose ...
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55 views

Back EMF protection

I made an ignition coil driver circuit which is nothing special - they are everywhere on the internet. What's really bothering me is the back EMF that would fry the 555IC. If I put a rectifying ...
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6answers
5k 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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3answers
4k views

Maximum Current Input for 555

I was looking over a datasheet for the NE555 Timer and I was wondering if the max supply current given under the electrical characteristics page is the max current you can supply to the 555 without ...
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2answers
123 views

Core rope rom not working

I am trying to make my own core rope rom, according to the link. I have 15mm ferrite cores, which I wound about 30 times with 1mm magnet wire. I thread the primary ( also 1mm wire) through one of ...
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2answers
54 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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1answer
101 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
39 views

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
63 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
300 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
46 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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2answers
217 views

how the calculate the specific resistor in a parallel led circuit?

This is a Sequential LED flasher circuit i found in you tube. He uses 11 leds in 5v power supply source and he connect them in parallel with a resistor 470ohms. I try figure out how he measure this ...
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2answers
147 views

voltage traces across pwm driven dc-motor: is that ok?

I'm driving a dc-motor with a BJT turned on and off with a 555 generated PWM signal. Here's the circuit (V1, Rl and L1 simulate the motor): There actual circuit - same parts - is on a breadboard and ...
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1answer
44 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
61 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
45 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
38 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
105 views

555 delay timer not working, it does not delay at all

My 555 timer is not working like normal. I don't really know what happened. I did this on a breadboard and it worked perfectly with a 5s delay at the deck. But now I am building a full circuit were I ...
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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
54 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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1answer
49 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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3answers
102 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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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
124 views

Can I use a current divider to protect my IC?

I designed an oscillator circuit using a TLC555 timer IC to create a 2 second pulse, which is used to drive a 12V 6W solenoid via a relay. Both the IC and the solenoid are run off of 12V, but every ...
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2answers
66 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
484 views

power on power off pulses to two seperate controllers

I would like to request a circuit where a 500 ms pulse is sent to one rail when 12 volt power is supplied and another 500 ms pulse is sent to a different rail when power is turned off. 555 is the way ...
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1answer
122 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
50 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
79 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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2answers
248 views

Why Arduino does not suit the to trigger a Spark plug but 555 timer can?

To trigger a spark plug and to control it using an Arduino, I tried following this really well-written guide. Basically, a MOSFET(IRF540N in my case) controls the closing and opening of the primary ...
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0answers
50 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
91 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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2answers
237 views

555 timer circuit switching automotive solenoid with PNP & NPN switching transistors

I am trying to design a 30 second timer circuit to switch an automotive solenoid that draws about 0.8 amps, and need some help please. StackExchange posts have been very very helpful so far, and by ...
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1answer
239 views

How can I use the component CD4538 or a 555 timer on Multisim?

How can I use the component CD4538 or a 555 timer on Multisim for a delay of 1 second ? I want both of the nor gates to be 1 for roughly 1 second when the output of the op-amps is either 01 or 10.
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68 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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2answers
3k views

independent control of frequency and duty cycle in 555 timer (formulas)

I want to control frequency and duty cycle of output pulse of 555 timer. I searched and find this schematic in a post in SOV but I don't know how calculate frequency and duty cycle in the circuit. ...
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4answers
5k views

Formula for Logarithmic (audio taper) pot

What I would like I am trying to determine the formula for an audio taper (logarithmic) pot. I would like a formula that takes R and P as inputs. R being the total resistance and P being the "...
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0answers
46 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
1k views

PWM and PPM using 555 timer

I get what PWM is and how it can be done using a 555 astable circuit. However I feel I don't completely get what PPM is how its circuit works. I understand the VCO circuit, but I don't see how it can ...
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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
52 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 ...