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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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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112 views

Capacitance via 555 timer & resonance. Sources and possible cure?

I apologise in advance if this topic has already been discussed here. I am no EE and have have no choice but to ask experts to move my project forward. I am developing a capacitive sensor via a ...
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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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59 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
91 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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56 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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1answer
40 views

Mono and Astable multivibrators not working when connected together

I have made a monostable multivibrator and an astable multivibrator using 555 timers using a popular circuit design found on the web. The monostable (out via pin 3) is used to control the astable (...
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1answer
67 views

PNP Transistor - Use IC 555's internal resistance as pulldown?

I have a circuit that uses a PNP transistor to enable or not the current to flow and turn on a LED. The point is, is it a good engineering practice to conect the base of the transistor to the Vcc of ...
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64 views

556 circuit not working

I just got my 556 timers and I wired it up just like the 555 but now: it flashes one HighTime and stays off then... I used this calculator and basic diagram: http://www.ohmslawcalculator.com/555-...
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286 views

Retriggering 3V PIR sensor with 555 timer circuit and LEDS

Hi y'all I'm putting together a PIR sensor circuit that will trigger a 555 timer in monostable and run a set of LEDS for about 5 sec all on a 3v cr2032 button cell battery and than reset until next ...
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2answers
239 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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136 views

Can I control the charge of a Cell-Phone with a 555 Timer and a Transistor?

I want to charge my phone in a controllable manner, using a 555 and a Mosfet transistor. The 555 is a countdown timer that gives an output (pin 3) of 5V for 1 minute, and then remains at 0V until an ...
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199 views

How to vary the range of a potentiometer…is this even possible?

I am a total noob so apologize if this doesn't belong here but I haven't had any luck finding an answer to this... I have a simple circuit with two 555 timers...similar to an Atari Punk Console. I ...
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320 views

Dark detector with 555 timer and output pin has a LED

I am a complete novice and I had done it in a hurry with my kiddo around. I have redrawn it, with the values I used. The circuit works. Also between pins 6 and 7, if I use a 100 K/10 K it works. ...
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121 views

clarification on a particular 555 implementation for 4017 johnson counters

I'm trying to build a 13 count johnson ring counter (which flashes LEDs sequentially 1 thru 13 and then repeats), and I found this circuit which looks perfect: I assembled it with an extra LED on the ...
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448 views

555 to debounce comparator output for PIR circuit

I'm trying to create a circuit that takes an input from a PIR and outputs a high signal when movement is detected. My circuit currently looks like the schematic below (VCC is 5V). The circuit works ...
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3k views

How to calculate the Ra and Rb values for the desired frequency and duty cycle?

I am designing a DC-DC boost converter for Vin = 5V to Vout = 15V. To generate gate pulses, I will be using a NE555P Timer by TI - http://pdf1.alldatasheet.com/datasheet-pdf/view/161277/TI/NE555P.html....
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1answer
51 views

555 NOISE BUTTON/ OP AMP

I have this circuit from the image below that I am designing myself. part of this circuit is cut so 2 78xx is present. This circuit is being designed and tested in parts. This part of the circuit has ...
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1answer
82 views

Power Latching Relay off/on in response to 12V ignition and 1 second ground pulse

I have the following sample schematic of a 12 volt automotive circuit to trigger about 60 seconds of power output to a latching relay on output pin 3 of the 555 Timer chip. The schematic below is a ...
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54 views

PWM with 555 timer IC

I am trying to build a PWM signal with 555 timer. I am following this website to build my circuit. simulate this circuit – Schematic created using CircuitLab I have placed my components in my ...
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29 views

Total Power Cutoff circuit

I'm designing a battery controlled circuit using a 555 timer to control a mosfet to provide power to a load. The problem I'm trying to solve is to reduce the current draw while the circuit is not ...
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46 views

Wireless power transfer circuit to attain ~5W of power on the receiving end

I am designing a WPT system to run a ws1812 based pixel chain. The ws2812 pixel chain runs on 5v and consumes 500-800ma of power, means 2.5w-4w. The system I made is not able to transfer adequate ...
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53 views

555 timed power at high to low edge in battery powered circuit

I have a lovely Atmel touch sensor whose output is high only as long as it's touched. I want both off-on and on-off edges of its output to initiate two 3 sec pulses (and the time between edges is > 3 ...
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49 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
31 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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59 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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2answers
62 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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1answer
112 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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2answers
79 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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53 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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72 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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48 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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79 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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66 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
120 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
37 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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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 ...
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1answer
82 views

Variable pulse train generation

I need to generate a pulse train with 12 bit resolution, controlled by an MCU. The duty cycle can be in the range of 30 - 40%, while the frequency (0.5 - 32 kHz) is what needs controlling with 12-bit ...
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1answer
57 views

How to make 555 timer output fall

I am using a 555 timer in the monostable configuration, which means that when I send a pulse to the trigger pin, the falling edge will make the 555 generate a high pulse on the output for some time. ...
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114 views

How to change frequency range of this circuit

I need to design a frequency to voltage converter and I found this circuit on internet: I removed the resistor R6 and the capacitor C5 because what I need is the PWM output it gives on the 555 timer. ...
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1answer
103 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
58 views

One time blink then turn off circuit

is it possible to change Circuit Diagram for the following example: http://www.redcircuits.com/Page146.htm or https://www.youtube.com/watch?v=mrxdiO1b29A Original: 4 short flashes stay on light ...
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1answer
29 views

touch switch time problem

I was looking for a way to make a touch touch switch and i found this circuit on the internet but the problem is , it goes off automatically after few seconds is there any way that i can control it ...
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1answer
44 views

monostable 555 timer - buzzer motor and pulsing

I need this circuit to pulse an LED while running a buzzer motor for an adjustable period RV1 and C1 should give me 1 - 5s of pulse, while RV2 and C2 should adjust the LED ramp times The LED will be ...
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45 views

Choosing Common Logic Level HF Buffer

I need help in choosing a common logic level buffer for a 555 timer output that will vary in frequency. I'd like to use n-channel/p-channel MOSFETs though I'm also open to cheap IC buffers. ...
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1answer
181 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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1answer
33 views

Time triggered switch off

I'm trying to figure a circuit design that when it is powered it outputs high. Then, when it get a pulse as input (low or high, I don't mind) it wait some time and then put the output to low. The ...
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51 views

Cannot share power source between audio module and 555 circuit

In this post, I outlined a circuit I was building to activate a solenoid with voice using a small Arduino sound detection module (this one). The output pulses from that module are too short to drive ...
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58 views

What's wrong with my boost converter circuit?

When I first created my circuit, everything worked fine. I didn't use a logic level mosfet at the time but I managed to acquire over 10V at the output (DC motor) and the next morning it stopped ...
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1answer
141 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 ...