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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2answers
47 views

Adding a buzzer to an existing LED

I have a set top box. It has a 3 mm green LED (on the front panel) that lights up when I connect the dish coax cable (signal LED). I measured the voltage across the LED. It has 0 V when the dish cable ...
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65 views

What is the purpose of the diode in this peak detector?

I was reading about a capacitive soil moisture sensor circuit today, and came across the following diagram: (Diagram taken from the Cave Pearl Project, https://thecavepearlproject.org/2020/10/27/...
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4answers
366 views

How to turn a normally-closed temperature control circuit into a normally-open one?

I've designed a very simple heating circuit that runs a heater until a certain temperature has been reached (as measured by an NTC thermistor) at which point the heater turns off. The circuit diagram ...
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56 views

Function of timer's output buffer

What's the function of the timer's output buffer?
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1answer
72 views

Astable multivibrator frequency mismatch

I made an astable multivibrator using an NE555p and a transistor. I checked the frequency and found it to be 220 kHz, but it should be 481 kHz. I used a resistor of 1 kΩ for both R1 and R2. The ...
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1answer
104 views

Does this circuit work to switch a load with a microcontroller?

I want to create a circuit to switch loads (e.g.: led lights). Following requirements have to be met: the load should keep it's state when the microcontroller goes to sleep/powers off the load could ...
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2answers
83 views

555 Timer with 50% duty cycle

I've seen below 555 circuit which produces a square wave of 50% duty cycle. I am quite new to electronics and I saw Ben eater's 555 timer tutorial where he used discharge pin for capacitor discharging....
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3answers
116 views

Pulse a 555 astable oscillator every second without an additional IC

I am developing a ranging device to help people with blindness. I need to pulse a 38 kHz Infrared LED every 1 second. A 555 timer in astable mode generates the 38 kHz modulation. I'm currently using ...
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2answers
675 views

555 Astable : Separate charge and discharge resistors?

The 555 astable oscillator seems to be usually implemented with one common resistor between the charging and discharging paths of the capacitor. Is there something wrong with putting one resistor for ...
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1answer
73 views

How to make a 555/556-based one-shot timer on a breadboard? [closed]

How can I implement the circuit as described below on a breadboard? The Monostable or “One Shot” Refer to the datasheet for the NE555 https://www.ti.com/lit/ds/symlink/ne555.pdf Find and read the ...
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56 views

Timer 555 AC square wave

Im currently trying to build a square wave circuit using the 555 Timer (see picture). Currently it is producing a square wave between 0 to 5V, duty cycle is about 50% and a frequency of about 50kHz. (...
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4answers
95 views

Making a simple 555 sawtooth VCO stable?

I have figured out how to make a sawtooth VCO using a 555 IC , by using a current mirror. The issues I am having is I can't make it stable at all. Its having random issues like it randomly changes ...
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How to stabilize this CV triggered toggle (555 timer latching switch) when fed with two gates?

I created the prototype for a modular synthesizer module. The project goal is an AND gate that is fed with two control voltage inputs (A and B with an Vpp around 5V). There will be two outputs: the ...
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2answers
133 views

Alarm circuit should be improved

I built an alarm circuit. The plan If a physical (door) contact (glued to the door) is interrupted (was disconnected by opening the door), an alarm should be signaled after 2 seconds. This is done via ...
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243 views

A couple of questions about a 555 in astable mode and a blinking LED

I would like to ask you guys to comment a bit. Does it work in real life? I would like to use a 555 in astable mode with the same time intervals for on and off (both 1s) and let a Vishay diode flash. ...
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66 views

Variable frequency pulse train generation

I wanted to create a pulse train of such a kind that the first pulse is high for a time=4x, then the next pulse is on for x, and the next for 4x... and so on. (without using microcontrollers/...
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165 views

4 way traffic light using 555 timer

I'm trying to build a 4-way traffic light controller in NI Multisim, using the 555 timer and a decade counter (no microcontrollers allowed). I used this as reference: https://circuits-diy.com/four-way-...
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106 views

Why is my piezo buzzer emitting a clicking sound?

I'm trying to make a voltage controlled oscillator (VCO.) It works just fine, but my piezo buzzer keeps clicking in conjunction with the square wave the NE555P is producing, making a weird effect. Is ...
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1answer
50 views

Why am I getting an "invalid expression" for output voltage and not for other voltages?

I have designed this monostable (one-shot) vibrator using the 555 timer, yet I am getting this type of error on Pspice for the output voltage only. Where have I gone wrong?
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1answer
65 views

Frequency calculation for 555 astable multivibrator

I am using the following circuit to provide PWM input to a dimmable LED driver. I need to know how can I calculate frequency and amplitude of the resultant PWM signal.
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87 views

555 PWM circuit set frequency shifting after 2 months

Please refer to post PWM generator circuit review for initial simulation and bugs on the circuit. In general, the circuit works very well and I can control a 12V fan with the PWM output of the 555 ...
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2answers
107 views

Converting latching switch to momentary output

I'm trying to get a latch switch to send a pulse for around 3 seconds or so. The pulse doesn't need to be pretty or precise. The circuit will be used to sound a buzzer when the switch is flipped on. ...
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6answers
605 views

Blink when input is constant?

I would like to have a status LED to make sure my microcontroller software hasn't faulted. From software, I will alternate an output so if it dies, the output will be constant. I want the status LED ...
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46 views

Grove capacitance soil moisture sensor

I have a Grove soil moisture sensor that works, but I have trouble understanding how the sensor actually works. I think the circuit starts with the 555 timer, that outputs a 487 kHz wave (R1 = 1.5K, ...
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1answer
91 views

Calculating time constant of a less than 50 % duty cycle 555 timer circuit

I am building a 555 timer circuit that generates a pulse for my servo motor. The circuit in mind looks like this: I got this circuit from this site, and it uses a (1N4148) diode, -the same one I ...
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1answer
79 views

555 timer monostable → simulation is not working

I would like to build a simple circuit with a 555 timer, in monostable mode (monoflop). I looked at these two diagrams for this purpose. http://www.learningaboutelectronics.com/Articles/555-timer-...
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145 views

Replacement for CD4017 / IC sequencers

I'm building this circuit from the image below, which is an LED sequencer. My problem is that where I am now I don't have a CD4017 to do the sequential, but I really need to make this circuit to ...
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1answer
78 views

555 Timer Switch Circuit Operating at 12V Problem

I have designed a prototype PCB for a product we are working on. It works, but with minor problem the PCB should be able to be supplied from anything from 5V - 12V. The problem is the 555 timer ...
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3answers
91 views

555 Astable output staying high

I have a ICM7555 with a 12 V supply in an astable circuit. When ENABLE goes high, I want my output to be high for a given amount of time, then carry on as a normal astable from there. So I have a ...
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45 views

Simple (variable) PWM generator for led driver that accepts PWM input

I have a cc(constt. current) led driver that accepts pwm input in the range of 2v-8v for led dimming.Can I provide this pwm signal from a 555 based pwm generator? If so how can I keep o/p pwm(from 555)...
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Understanding a 555 timer PWM schematic

I'm tinkering with the circuit described in Dimming the nixies but am confused by part of the schematic shown (highlighted below) What are the potentiometer connections being described here? Is there ...
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1answer
138 views

Mystery short in piezo driver circuit

I'm building a circuit to drive a 113 kHz piezoelectric mister. When I apply power, it appears the circuit is shorted. My regulated lab power supply hits the 1 A limit I set, though it should consume ...
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2answers
135 views

TLC555 design calculator

I need to generate a square wave at 600 kHz with the TLC555. In the datasheet (7.3.2 Astable Operation) TI advise us to use their calculation tool for the frequencies above 100 kHz. I downloaded it ...
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5answers
1k views

50% 555 cycle - comparing two diagrams

I'm getting started with an electronics project that's a bit more complicated than a simple pull-up and pull-down, using the 555. I've been reading up on it, and I think I understand how it works, but ...
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3answers
150 views

555 timer Bistable circuit not working as suggested, bad circuit?

I'm using an app to explore different 555 timer uses and getting my head around the logic. The app states that this circuit will flip-flop the two LED's on each press of the button, but I can't see ...
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1answer
94 views

PWM generator circuit review

I've designed the following circuit in order to control a 12V fan with PWM. The circuit is meant to stay at a fixed frequency of around 25kHz but a variable duty cycle controlled by a potentiometer. ...
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1answer
136 views

How to boost the strength of AM transmitter made using 555 timer?

I have finally started my journey of learning something new about our everyday radios and their functionality by making an AM radio transmitter using the 555 timer. I am trying to understand how LC ...
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3answers
91 views

Restarting a 555 timer

I recently came into ownership of a (sort of) arcade machine and I'm looking for a little help to figure out if it's possible to modify it. Long story short, the coin-op uses a simple circuit composed ...
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2answers
118 views

Are 7555 inputs protected internally by diodes?

I've tested the inputs of a 7555 with a diode tester and I could read a 0.7V/0.6V drop between each input and GND and each input and VCC. Something that suggests that they are protected for over/under ...
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1answer
65 views

Astable 555 Timer how to create longer pulse at reset/beginning/turning on

I would like to build simple 555 based fan controller. The requirements are: at start the controller generates one longer pulse (which can be configurable) after one longer pulse it generates PWM ...
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2answers
71 views

Issue with a touch switch

I made a touch switch in PCB based in the following schematic When touching the plate with a finger the BJT turns on and the 555 trigger pin goes LOW activating the pin 3 (OUTPUT). The time the ...
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4answers
208 views

Would using the output of a 555 timer to charge/discharge its capacitor work?

Background I'm relatively new to electronics and playing around with a 555 timer. I found that for astable operation, all sources I've seen recommends the following design (with different resistor and ...
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2answers
103 views

traffic lights with 555 and 4017 (only red led light up) solution

I have been trying to simulate a traffic light circuit (UK version) on tinkercad. However ,only the red led lights up . Any ways I can resolve the issue? Thx The schematic i used : scheme (mine) : ...
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1answer
54 views

Can someone explain this trend of Control Voltage Vs Output Freq? Circuit configured:- 555 IC as a VCO

So, in my Master's, while going through a lab for analog electronics, we were given this seemingly pointless task of plotting Control Voltage vs Output Freq when a 555 IC is configured as a VCO. The ...
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1answer
62 views

What function does this resistor/capacitor arrangement provide in this reset circuitry

I have been trying to decipher what the arrangement of the resistor and capacitor does in the circuit below, but I am at a loss to explain it. Can someone explain to me what it is doing? The circuit ...
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1answer
67 views

Are 555 PWM circuit resistor and capacitor values independent of the voltage applied to a 555?

I am new to electronics so my question sound dumb. I am using this diagram to build a 555 timer IC PWM circuit: The above circuit operates on 9V but I have 5V. Do I need to change capacitor and ...
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1answer
58 views

How to connect the output of the 555 in monostable mode to an optocoupler?

I currently have the following schematic for my circuit: Link to the simulation. On the simulation everything is working pretty good. The output of the 555 which is in monostable mode is giving ...
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2answers
80 views

555 PWM Checker/Filter

I need to design "PWM Checker" or filter - that will check that the input signal is at specific frequency (let's say 1 kHz) and specific duty cycle (let's say 33%) and the design has to use ...
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133 views

Traffic light tinkercad

For a project I am trying to make a traffic light circuit using two 555 IC chips. However, the output I am getting (green > yellow > green > red > green > yellow > red) instead of ...
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2answers
227 views

4-wire fan controlled by potentiometer and 555 IC not behaving properly

Here's the schematics: Forgive me for the newbie schematics. This is the first time making one. I used an LMC555CN IC and this Delta BFB1012VH-5D84 Blower Fan (Can't find a datasheet for this one). I ...

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