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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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
80 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
254 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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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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94 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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255 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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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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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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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
76 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
57 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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2answers
113 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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1answer
123 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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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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689 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
92 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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60 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
76 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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1answer
4k views

Flyback transformer

Recently, I posted a question about a flyback transformer schematic I was having. (source: eleccircuit.com) If you didn't check the link, I was having problems with the frequency of the 555 timer ...
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1answer
162 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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2answers
2k views

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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3answers
5k views

Why does this circuit keep killing my 555 timers?

I have a 555 timer set up in a standard monostable oscillator configuration. Nothing fancy, no modifications whatsoever. I'm driving it with about 12V. If I trigger the 555 with the ground directly, ...
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1answer
170 views

555 circuit problem.. could it be broken?

I've made a circuit that's connected to a 12V+5V power source (attached a gallery. last photo is the schematic) it is simply a 555 timer that goes off whenever one of the two input pins goes high (...
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53 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
156 views

PWM controller circuit Issue

I'm having an issue with this PWM controller circuit. In this circuit the potentiometer comes with a on/off switch. The way it should work is: As the potentiometer resistance value varies the output ...
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2answers
142 views

Dc Motor circuit

I am making a motor control circuit for my model plane engine. It has to start slowly and climb to its full power and stop slowly like a jet engine fan. I saw a video on YouTube called 'super ...
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0answers
63 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
83 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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2answers
31 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
71 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 ...
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1answer
57 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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3answers
9k views

Determine suitable resistor for the base of transistor as switch (NPN)

I have designed a program to count the frequency and time period of the pulse generated by a 555 timer IC using PC Parallel port. I’ve connected a base of BC547 (NPN) transistor to the output pin (no. ...
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2answers
136 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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1answer
79 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
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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3answers
123 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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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
81 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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2answers
4k views

How can I prevent a 556 timer IC from becoming very hot?

I built the circuit described in a previous question/answer which I will repost here: It's been running quite well, actuating the solenoid at regular intervals as designed. The TIP122 transistor is ...
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37 views

Switching timer delay, non accumulative

I am trying to build a 555-timer that delays the switch of an input signal, both ways. When input goes high there should be a delay before output goes high, when input goes low there should be a delay ...
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1answer
254 views

555 IC - Transistor Tester

Why are Pins 7 and 5 floating for this 555 IC and how does an NPN and PNP transistor when connected to E B C act a switch? Without the use of Pin 7 surely the capacitor cannot discharge which would ...
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2answers
103 views

Trouble with engineering project - 555 timers

I'm currently finishing my GCSE engineering project and I am attempting to use a dual 555 timer circuit as a timer. I am using a schematic I copied off Kitronik Alarm Project Kit, but when simulating ...
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6answers
2k views

555 timer FM transmitter

So online, I found this 555 timer FM modulator circuit. But To make this a working FM transmitter, is all I have to do is attach an antenna to the output modulated signal? Or do I have to also have a ...
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2answers
84 views

Inverting input of 555 timer

The common 555 timer triggers the output when the trigger signal falls down. Although this is not a problem, I want it to do the opposite, which is to trigger when the signal that controls the 555 ...
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3answers
67 views

Why output is high even though trigger pin is high in Proteus simulation of IC555?

In the below attached circuit of IC NE555 Proteus 8.0 simulation, TRIGGER pin (Pin 2)is set at Vcc. So why the output is high? It should be low since voltage at TRIGGER pin (Pin 2) is more than 1/3 of ...
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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
64 views

555 timer square wave LED flasher

Will this circuit work for the purpose of making a high voltage LED flash on and off at 10kHz? I have a NPN transistor to turn the LED on and off. The pad is where the LED will be soldered into as ...
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1answer
53 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. ...