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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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2answers
126 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
119 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 ...
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1answer
80 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
237 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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2answers
77 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
61 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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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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1answer
39 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
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. ...
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0answers
78 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
62 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
199 views

NE555 and LDR circuit diagram

I have modified a schematic for my project with the following image: Instead of a 20K potentiometer, I use 100K for more precise adjustment. Do I need to add a disk capacitor of 10nf or 100nf to Pin ...
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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
127 views

Hall Effect pulse multiplier circuit

I would like to use a Phase Locked Loop (PLL) to multiply a 4x signal to be an 8x signal, and modify the same 4x signal to be a 64x signal so that all three signals are available as a 5v clean low - ...
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1answer
57 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
54 views

SIMPLE digital control over 555 timer frequency and PWM?

I'm looking to create a sound generator with only simple ICs and components. I believe the 555 timer IC is a good candidate to be at the core of it, but I cannot for the life of me find out how best ...
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1answer
27 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
42 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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1answer
63 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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3answers
189 views

Eliminate AC noise from DC supply?

I have built an automatic water tank using the circuit given below: But this circuit was working well for 2 days. But after that, it triggers falsely. When a fan in another room is switched on, this ...
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1answer
44 views

driving a medium power darlington transistor with the output of a 555 timer

Question: What is the limitation on the output of the 555 timer with respect to the requirements of the input of the BDW42G? Can the 555 provide enough current at 5 volts to trigger (sufficiently) ...
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3answers
108 views

How to convert 8-bit information containing MIDI note, to square wave signal using basic chips and components? [closed]

Using basic electronic components (capacitors, transistors, etc) and/or chips (555, 74 series, etc) how do I convert from: Input: 8-bits containing the binary representation of a MIDI number "...
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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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0answers
107 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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2answers
1k views

What is signal ground

I encountered signal ground symbol while studying 555 IC Please explain why isn't a simple ground connection used and how does signal ground differ from normal ground. I am a first year undergraduate, ...
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2answers
109 views

555 Timer PWM generator

I have the following circuit for a 555 Timer PWM generator: With 1: GND, 2: TRIGGER, 3: OUTPUT, 4: RESET, 5: CONT, 6: THRESHOLD, 7: DISCHARGE, 8: VCC I dont quite understand the use of R1. Is it ...
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0answers
43 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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2answers
224 views

Why isn't my 555 cascading timer working?

I've made a 555 cascading timer. First stage is approx 90 seconds, second is 30 seconds. The first two led's light up in sequence as expected, but the 3rd doesn't light. I've checked all connections. ...
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2answers
111 views

Where to connect unused 555 timer ICs pins?

simulate this circuit – Schematic created using CircuitLab This question might not have a close answer since I think it heavily depends on the considered pin and IC. However, consider, for 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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1answer
158 views

3 simultaneous led chaser using only 555 and 4017

I've to design a circuit which consists of 30 LEDs in a row (RED, BLUE and GREEN) followed by a led matrix which spells out IN. Conditions which I've to follow: When the circuit is powered, ...
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1answer
30 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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3answers
52 views

Using the same components for two 555 timers

I am building a circuit to operate a Linear Actuator to open and close a lid. The open and close times are the same. The standard monostable circuit works. There is one switch to tell if the lid is ...
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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
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
56 views

Nautical map model navigation lights

I would like to create navigation light sequences on old admiralty map of my local area. There are lighthouses and channel markers in area with mix of flashing and times. The single flashes I can use ...
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2answers
79 views

How can I dampen current spikes when using NPNs to drive an LED

Hi I have the following circuit, its purpose is to flash an LED once per second. I'm using a pair of transistors as a constant current source but I observe current spikes of 20% or so when it is ...
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1answer
202 views

12V PWM controller for 12V fan that gets faster with the COLD

I need a controller for a 12 V - 1A fan, blowing on the cold side of a Peltier element to keep it at constant temperature. I have the hot side under control. I have seen multiple cheap PWM ready-to-...
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2answers
66 views

555 timer circuitry

I have a 555 pulse generator controlling a relay going a little faster than 1hz. It is hooked up to start up when it receives positive voltage from the switched accessory circuit of a vehicle. That ...
2
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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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3answers
502 views

555 Clock Circuit - how to choose resistor value? [closed]

I need to design a 555 clock circuit to output a clock pulse of a specific frequency. The circuit I'm using is this one (from here): I've used this circuit before and it works fine but the website ...
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5answers
112 views

Will this 555 circuit prevent a car from disconnecting power to the radio when starting?

To start with I'm a little rusty with electronics, I haven't done much in 20 years and it was only a hobby back then. In my car I have a head unit with a touch screen which relies on software to run ...
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1answer
69 views

Addition of limit switch for power supply stops circuit from working. Circuit works fine without the switch?

I am having an issue with a limit switch to turn on and off a circuit. I am using a L7805 5V regulator with a regular 9V battery as the power supply for my circuit. When I plug in the 9V battery ...
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0answers
50 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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0answers
54 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
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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1answer
61 views

High and Low times for 555 oscilator are inverted

I’m new to electrical engineering and this is my first time working with an oscillator. I'm trying to setup a 555 timer ic as an oscillator with a low time of 1s and a high time of 0.5s. I've been ...
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1answer
76 views

IC 555 as monostable multivibrator

How is the output of a monostable multivibrator affected if the trigger pin is kept at a negative voltage (0V)? The upper voltage reference comparator will change its output to logic 1, while the ...