# What is 555 timer: Definition and 50 Discussions

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, delay, pulse generation, and oscillator applications. Derivatives provide two (556) or four (558) timing circuits in one package. It was commercialized in 1972 by Signetics. Numerous companies have made the original bipolar timers and similar low-power CMOS timers too. In 2017, it was said over a billion 555 timers are produced annually by some estimates, and "probably the most popular integrated circuit ever made."

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1. ### Object detector using ultrasonic sensor with 555 timer

See the attached figure. I used 220uF with buzzer and also tried 10uF capacitor but buzzer isn't loud enough. I don't have any 3.3pf capacitor. I used 1.1 pF instead. I also tried changing the resistance of potentiometer but still buzzer isn't sound loud enough.
2. ### Capacitive soil moisture sensor using TLC555

Hello everybody, I have made soil moisture sensor and it kinda works. It is a capacative sensor not resistive sensor based upon TLC555 which has a role to create square wave. Square wave is brought to a homemade capacitor. Capacitance changes with change of moisture. Output is measured voltage...
3. ### Engineering RC Circuit/Node voltage question

Homework Statement Homework Equations The Attempt at a Solution So you need to find the voltage across node D while the capacitor is charging, so it is going to be related to the voltage of the capacitor, so a function of time, so you need to come up with the equation for Vc(t), which I...
4. ### 555 timer, 50% duty cycle astable, run from 5V

Standard disclaimer: I know next to nothing about electronics (which doesn't stop me from having fun :wink: ) I have a buzzer here that I am trying to run from an 555 based oscillator. I need around 2700 Hz and 50% duty cycle, and it would be best to run whole thing from 5V. 50% duty cycle is...
5. ### Build a Lightning Cloud with a 555 Timer | LED Flashing Help

Hello, I have been in the process of building a small lightning cloud out of Poly-Fil and some LED's. I have looked up on how to build flashing LED's with a 555 timer, and I have tried (many) times, yet every time I hook up the 9v battery, my LED either turns on, but does not flash, or doesn't...
6. ### 555 timer IC - Calculating resistance needed

Voltage = 9.0 V, Current = 20 mA, Capacitor (C) = 10 microF, Resistance before (too high) [R_A = R_B] = 10 k Ohms. In a a-stable oscillator, calculating the resistance needed for two resistors (R_A = R_B) to discharge and charge a capacitor (C) so that a LED does not blow. Currently my circuit...
7. ### 555 timer question & Bounceless Garage door opener.

555 timer question & "Bounceless" Garage door opener. When opening a garage door from a distance, it is sometimes necessary to push the button multiple times when beyond the range of the transmitter. One can inadvertnently push the button multiple times and cancel the door going up. To open...
8. ### Transistor connection in the discharge path of the 555 timer

http://www.slideshare.net/viv3ksharma/automatic-school-bell In this circuit I Think the emitter and collector terminal of the transistors T1 & T2 will be reverse. Otherwise the 555 timer will not discharge. Can anyone help pls?
9. ### What happens when the switch is closed in a 555 timer and left there?

Here's my circuit The question at hand is what happens when the trigger switch is closed during the timing cycle (after being closed once already to initiate said cycle) here's the waveform I'm getting, but I'm not sure what to make of it. could someone please help me understand...
10. ### Making a Blinking LED 555 Timer

Hi guys, I figured I might try making a LED to phase on and off for around 1 second, to be perfectly honest I have NO idea what I'm doing really. But figured that's the best way to learn right :P. So I'm using a Timer 556 and connected it in a way that kind of made sense from the 555 IC timer...
11. ### Tesla coil with 555 timer troubleshooting help

I attempted to build a tesla coil with a 555 timer but seemed to have failed some where. Perhaps you could take a look and give me some hints on what to try in order to make it work. I attached some pictures as well. I made the secondary coil on a 1/2 (.875 OD) pvc pipe with a 10 to 1 ratio...
12. ### Troubleshooting a 555 Timer Circuit with Added LEDs | Circuit Issues & Solutions

Hello, I have designed a circuit based on one that I found on the internet (attached as example.gif). This circuit worked well when I built it on a breadboard. I made a few minor modifications to the example circuit (attached as schem1.bmp) and I am having a few issues that I do not...
13. ### Request help with 555 timer circuit

Hi all, I would like to make a 555 timer circuit that when 12v is applied to the circuit an LED will light for 3 - 5 seconds and then go out. and remain out until the 12v is removed and reapplied. Any help greatly appreciated. Thanks
14. ### Clap Switch using 555 timer in monostable mode(Values of components))

Hello Experts! Here is my simple clap switch schematic. First let me know is it correct or not? I have used 555 timer in monostable mode here this means LED will remain on for the particular period of time defined by R3 and C1 i.e. T=1.1(R1)(C1). Let I use red LED here. So I think 1.7V is...
15. ### Monostable and Astable multivibrator using 555 timer.

Hello experts! I have given 2 question in exams. 1)Explain why duty cycle of Astable circuit's output is always greater than 50%? 2)In monostable multivibrator, how low does the triggering voltage have to go in order to initiate the output pulse and why duty cycle must be greater than...
16. ### DC to AC inverter using 555 timer

I want to know the function of the two power amplifier ?
17. ### Just another monostable 555 timer question

Just another monostable 555 timer question :D I have a 555 monostable circuit with a relay attached to + and pin 3. I tried attaching it to pin 3 and - but it didn't work. Anyway, its very temperamental and keeps going that when you push the button it will stay on for about 2 seconds or less...
18. ### Investigating Erratic 555 Timer Behaviour with Digital ICs

Since I don't have a function generator, for some experiments at home with digital ICs I've used a 555 timer with 5V Vcc as the clock, and I noticed something problematic. It behaves rather erratically. I've mostly been using it to trigger a 74LS90 asynchronous 4-bit counter. Sometime it works...
19. ### 555 timer Astable not working, only One LED is lit up

I have been trying to make this circuit work for a few weeks now and it is slowly driving me crazy. I have on a veroboard a circuit. When i redo the circuit on Yenka (Crocodile clips) It works perfectly. The circuit is a 555 astable circuit with two LEDs, when i turn it on only one LED...
20. ### Using a 555 timer as an analog frequency divider?

Hey guys, I'm trying to build a circuit where I can put in an analog signal (my voice) and have it output the same signal with a much lower pitch (speech synthesizer). Is there any way I could do this with primarily a 555 timer? I'm able to pulse width modulate the analog signal, but I...
21. ### Solving 555 Timer Equations Homework

Homework Statement Hi, I've been working with 555 timers for a project on my coop and I've been running into some problems. I don't think the simulation models are not ideal or great representations of the real thing, but one of the problems I've been having is trying to work out the the...
22. ### Creating a 555 Timer Circuit for Motor Control

Basically what I'm trying to do is have two LDRs connected to a differential op-amp. The configuration has it high when LDR1 is low and LDR 2 is high with the rest of the combinations outputting low. Theres two op amps connected so that there are two distinct output channels so i have two high...
23. ### 555 timer circuit; frequency variation

I conducted an experiment involving a 555IC timer circuit and the hypothesis investigated the frequency and period of the LED connected. Using the formula for frequency; 1.44/(Ra + 2Rb)C where R1= 1000R R2= 10000R C = 10uF the frequency equals 6.857 (rounded value) now using data...
24. ### 555 timer strobe light not working

Hi, I have a circuit that I am working on that I adapted from the 6v version here http://electronician.blogspot.com/2009/09/555-timer-project-15v-led-flasher.html I have a 12v supply with a total of 48 leds 24 on each bank. I have gotten previous version to work with single leds but now that I...
25. ### Help with 555 Timer Chip & 38 kHz IR Light

Hey all. I am using a 555 timer chip to power an IR LED, which switches something on or off. My question is, now my timer chip is sending out 38 kHz IR light. My IR receiver is made to pick up 38 kHz IR light, but only the first 14 (I think) pulses, then ignores all pulses without a pause...
26. ### Problem with my HA17 555 timer

i recently bought my 555 timer and i simply can't get it to pulse. I flick on the switch and i get my buzzer to work that is connected to the output but i don't hear it turn off and on. I set my configuration as astable 6.5 Hz. i checked all my connections and everything seems right. However...
27. ### Question about a circuit using a 555 timer

Here's the drawn circuit: http://imgur.com/DGo9M.png R1 is 10k Ohm resistor Pot is a 100k Ohm potentiometer C is 1.0uF Electrolytic Capacitor My question is, what happens when the potentiometer is turned down to 0 resistance? Would the circuit fry? thanks
28. ### 555 timer internal schematic questions

hi everyone, i am trying to build a very high current dc to ac inverter and i can't use a 555 timer IC because they can't source or sink but a maximum of 200mA, but i have found an internal schematic of the 555 timer IC online and have been studying it to see if i can build a very high current...
29. ### Need help with confirming if this 555 timer circuit with transistor will work?

I am an electrical engineer student at SIU and I'm working on an personal project where I am trying to use the following items to supply current between 450-600 mA: 555 timer 2N2222 transistor 4 AA batteries in series for 6V Resistors and capacitors on 555 timer while just resistors on...
30. ### Frequency question - 555 timer driving a transducer

1. For a school project we're building an emergency braking system. In addition, we also want to trigger an audio-visual alarm system to alert a third party to the operation of the system. For the alarm system we are using a 555 timer to generate a squarewave output to alternate a buzzer between...
31. ### Perfecting the 555 Timer: Adding an LED Display for Precise Liquid Dispensing

I want to first thank all of you for your help with my first 555 timer question. With that help and some more reading on the net I have it working perfectly. My next task on this timer project was to include an LED display. My intention was to have a display that would give me a numerical...
32. ### Troubleshooting 555 Timer Circuits

I have been having a great amount of difficulty with the 555 timer (Texas Instruments NE555P). I am going through a book published by McGraw Hill titled Understanding Electricity and Electronics. While I was waiting for the parts to finish my power supply, I started to work with the 555 timer...
33. ### Why is my 555 Timer not blinking?

Hey Everybody! I have been using this page as a guideline to learning how to use a 555 timer: http://www.kpsec.freeuk.com/555timer.htm I have been trying to make an LED flasher by using a 555 Timer for the first time, but after 2 days, I have been unable to see my problem. I am using...
34. ### 555 Timer RC Charging Capacitor Conundrum

Hello. I am currently trying to evaluate just how much power the external RC circuitry of a 555 timer uses over 1 cycle. Whilst the capacitor is charging the current falls exponentially. Naturally the voltage also falls through the resistors but this is couteracted by the rise in voltage of the...
35. ### How can I prevent false triggering in a monostable 555 timer circuit?

I am having trouble with a mono-stable 555 timer circuit. When I connect this to a power supply (right now it is a 120VAC to 12VDC converter), the timer turns on and then off, like it would have if it was activated by the trigger. After this, when the trigger is used, everything works...
36. ### Solving 555 Timer Issues with RH Over 45%

Hi I am currently using LCM555 timer for generating variable frequency based on relative Humidity (RH) of surrounding. The LCM555 is configured as astable multivibrator and centered at 20KHz. RA = 24K, RB = 200K and C is capacitive sensor having value of 160pF at 30C, 0%RH. The C is given by...
37. ### Want to Program a 555 Timer? Here's What You Need!

Hi guys I want to learn how to program a 555 timer. I searched google and there doesn't seem to be any sort of tutorials or good info for a beginner to get started I don't even know what equipment I would need to do it. I want to program a 555 timer for 15 pulses per second so I can make...
38. ### DC-DC Buck-Boost converter using 555 Timer?

Hello All, I'm working on a project that requires an isolated switching supply that will output 15V from a 9-18V input at up to 2W. I have found the perfect DC-DC converter module for the job from MicroPower Direct but I'm trying to see if it would be possible to build something with similar...
39. ### Creating a 556 Timer from Two 555s - Possible?

Is it possible to create a 556 timer from two 555 timers rather than just purchasing one 556? Thanks
40. ### Can the 555 timer be set to its maximum frequency of 500kHz?

How would i do this?
41. ### Producing a Time Delay of 44 Seconds with a 555 Timer

Hi, everyone. I am currently involved in a small electronics project and I am required to produce a time delay for part of the project. I plan on using the famous 555 timer and not quite sure on what to do to produce this delay.So please anyone help explain how to produce a time delay of,say...
42. ### Triggering 555 Timer: How to Use PIC Microprocessor

hey guys... I'm having some trouble trying to figure out how to trigger a siren I'm working on. i have an astable circuit setup with the output of the monostable 555 connected to the output of the astable 555s to trigger the circuit. i wanted to trigger the circuit using a PIC microprocessor but...
43. ### Solve 555 Timer Problem - Get 100kHz & 95% Duty Cycle

[SOLVED] help 555 timer problem hi all, i am designing a 555 on astable mode. it is designed to operate at 100kHz with a duty cycle of 95% ( and i get 48Khz and duty cycle 93.5%). i calculated all the values necessary: Ra = 12.987 kOhm Rb = 721.5 Ohm C = 1nF F = 1.44/ ((Ra + 2Rb)*C)...
44. ### Timing control for motor using a potentiometer

I need help buiding a circuit that would use a potentiometer to control power from a small battery (AA's, 9 volt, or similar) to a small electric motor. I would like to have the motor pulse on for @5 seconds and then go off. The 5 seconds "on" would remain constant, but I would like the pot to...
45. ### Engineering Resistors in a 555 Timer Circuit

I was using a 555 timer circuit to generate a tone the frequency of roughly 256 Hz with resistors of 22 and 270 Ohms and a capacitor of 10 uF but I was advised not to by my teacher and wasn't able to ask the reason why. Can someone kind of brief me on this since my teacher is away tomorrow and...
46. ### Troubleshooting Monostable 555 Timer Circuit

So I will start off saying that I am not a genius when it comes to this stuff quite yet, but i have done several EE classes(slow but its going) and tinker around for fun. But for some reason this 555 Timer(i have a 556 Dual Timer) is just not working and i can't tell if its a faulty chip or...
47. ### Simple 555 timer circuit needed.

Hi all, great forum here. Hope to learn a lot. I am looking for a sample LM555 circuit. In simple terms I am looking what I think to be a reverse of the monostable circuits I have seen. More or less I have a switch that needs to be held down for 1 sec before the circuit is active (pin 3...
48. ### One time Pulse with a 555 Timer

Hello I currerntly have this circuit - https://www.physicsforums.com/attachment.php?attachmentid=8419&stc=1&d=1164497449 circuit1.jpg I am trying to keep it as simple as possible. I have scoured loads of site etc, an have even found the circuit I want, or should I say it is described as the...
49. ### Using 555 Timer IC to Output 100 KHz Frequency

Hi, I have a 555 timer IC. For my work, my colleague asked me to make it so it can output 100 KHz frequency. (astable) My Ra = 6.8 kOhms and my Rb = 4.7 kOhms... I know that the Frequency = 1 / (T_high + T_low) where T_high = 0.693(Rb + Ra) * C T_low = 0.693(Rb) * C Although I'm not...
50. ### Learn How to Program a 555 Timer for 4 Second Intervals | Tips and Tricks

Hi! I need to programme a 555 timer pulse with intervals of 4 secs. I've already tried connecting a monostable circuit I found on the net with values of a 36K resistor and 100uF capacitor but what's happening is it's going on for 4 seconds then off for the rest! Here's the circuit that I...