Adjustable Timer Using IC 555

A timer is a device which produces a delay period after which an external connected electrical load is triggered.

 Configuring a Timer Circuit using IC 555

The produced time delay is normally adjustable and the user has the freedom to set the time period as desired.

There are many ways of making simple timer circuits using different ICs and discrete components; here we discuss one such circuit using the ubiquitous IC 555.The IC 555 is a pretty common electronic part among the electronic enthusiasts and is also very popular due to the involved simple configurations and low component count.

The two popular multivibrator modes of operation that’s associated with this IC are the astable mode, and the monostable mode. Both of these are useful configurations and have plenty of different applications.

Using the IC 555 in Monostable Mode

For the present adjustable IC 555 timer circuit design we incorporate the second mode of operation, which is the monostable mode.

In this mode of operation the IC is configured to receive a trigger externally, so that it’s output changes state, meaning if with reference to the ground if the output of the IC is zero, then it would become positive as soon as the trigger (momentary) is received at its input terminal.

This change in its output is sustained for a certain period if time, depending upon the external time determining components. Normally the time determining components are in the form of a resistor and a capacitor which together determine or fix the time period for which the IC output would hold its “high” position.

By changing either the value of the capacitor or the resistor, the timing can be altered as desired. The above time fixing components are termed as the RC component.

simple IC 555 based timer circuit

Note: Please connect the buzzer or the load between pin#3 and ground, and not between pin#3 and positive as incorrectly shown in the above diagram.

How the Circuit Functions

The 555 IC timer circuit above shows a very straightforward design where the IC 555 forms the central controlling part of the circuit. As discussed in the above section, the IC is in its standard monostable mode.

Pin #2 receives the external timing trigger from a push-to-ON switch. Once this switch is pushed, the circuit pulls its output to a positive potential and holds it until the predetermined time delay lapses.

The entire circuit can be built over a small piece of general PCB and housed inside a neat looking plastic enclosure along with the battery.

The output may be ideally connected to a buzzer for receiving the warning alarm after the set time lapses.

Parts List

R1, R4 = 4K7,

R2 = 10K,

R3 = 1M pot,

C1 = 0.47uF,

C2 = 1000uF/25V,

C3 = 0.01uF,

IC1 = 555,

Bz1 = Piezo Buzzer,

Push Button = push to ON switch circuit design requested by Mr.Bourgeoisie:

simple IC 555 timer using external trigger

Please connect the buzzer or the load between pin#3 and ground, and not between pin#3 and positive as incorrectly shown in the above diagram.

Timer Circuit with Relay Switching

If you are wondering how the above simple timer circuits could be used for triggering a high power load through relay switching, then the following diagram will help you to implement the same by attaching a simple relay stage with the shown designs:

simple IC 555 one shot timer circuit using push button and relay

Simulation and Working

In the shown diagram, when power is switched ON, the IC goes into a standby state, and no triggering action is initiated at this moment.

However as soon as the push button pressed, pin#2 is pulled down to ground which instantly triggers the IC in the monostable counting mode, and the relay is activated. The load connected with the relay is thus also activated.

The IC starts counting, and depending on the values of R3/R4, and C2, once the timing period gets elapsed, the IC resets to the previous standby mode deactivating the relay. The relay load also gets deactivated in this situation.

The cycle repeats each time the push button is pressed, enabling the user to achieve the relay triggered timing ON OFF feature in the circuit.

The timing interval can be increased or decreased to a given extent by suitably altering the pot R3 value and/or by modifying the value of C2.

Need Help? Please send your queries through Comments for quick replies!


Ben Langat said…
Hi swagatam ,I wanted to construct a circuit which uses a small voltage of less than one volt to control a relay of 12 can I go about?
Swagatam said…
Hi Ben,

You can try a relay driver circuit as shown here:
Swagatam said…
You can try this circuit:

You will have to remove D2 and replace the triac with a transistor/relay driver stage, after that the variable may be set for achieving the required timing.
jaejjii said…
Hello sir, I have formed this circuit in multisim 12.o. i have the muscle stimulator as the other circuit. can this muscle stimulator be the trigger?? if i put these two circuits on 1 board in multisim, will the result show??
jaejjii said…
Hello sir. I just wanna ask if i put this circuit and a muscle stimulator circuit as the trigger in multisim 12.0, will the result show, like the buzzer would buzz? or it should be done physically to know the results??
Swagatam said…
Hello Jaejjii,

I don't think the simulator would be able to simulate your muscle simulator response along with the above I think you should test the configuration practically.
nitin rajpoot said…
hello sir...fist of all thank u for running such a nice blog...sir i want to make a three light running chaser to be worked on ac lights...and want to keep interval switching time 1 minute...pls pls help me sir....thanxx
Swagatam said…
Helo Nitin,

I have explained it in your previous comment with a link....for 1 minute interval you just need to adjust the pots carefully for the required timing.
Swagatam said…
You can try the second circuit given in the above article, do the following modifications in it:

Remove the buzzer, and put a relay across pin3 and ground.

Remove the transistor and replace the position with a 0.22uF capacitor, also put a 1M resistor in parallel with the above cap.
The timing can be set by adjusting the shown preset.

Whenever power is switched ON, the relay will hold and then deactivate after the delay period has lapsed.

The reay contacts may be wired up with the hair dryer.
Abu-Hafss said…
Hi Swagatam

Would you please tell me the functions of D1, D2 and R1? I have just blew a 555 without them.

What would be the configuration for a positive triggering signal?
Swagatam said…
Hi Abu-Hafss,

R1/R2 are for discharging C1 so that it becomes ready for the next input pulse

D1/D2 are not crucial and may be removed, these are for restricting the entry of high frequency disturbance at pin2 and for eliminating false response by the IC.

There's no way you can blow this IC, unless you short circuit the output for too long or reverse the supply polarity.....
Swagatam said…
You will have to construct it first and then check it as per the given instructions, that's all. If you face problems while troubleshooting I'll help you.
Abu-Hafss said…
Hi Swagatam

I am really exhausted, I admit, I have failed. Please help me.

I need two monostable 555 timers configured such that:

1) when switched on, ONLY the first timer should be triggered automatically
2) after completing its preset time the 1st timer triggers the 2nd timer
3) after completing its preset time the 2nd timer triggers the 1st timer
4) hence the cycle repeats indefinitely

Just let me know how to connect the pin #2 of both timers.
Swagatam said…
Hi Abu-Hafss,

I'll do it for for but in return you will have to explain the circuit in your own words, ...agreed?
Abu-Hafss said…
Actually, I had made the circuit; and as per my usual practice I simulated in 2 different softwares. One worked perfectly, but the second one (LTSpice from Linear Technology) did not accepted. And I mostly rely on LTSpice, which I consider to be much accurate.

Here is my circuit
Swagatam said…
Hi Abu-Hafss,

The trigger inputs are not configured correctly in your circuit according to me, I'll try to update the correct one soon.
Swagatam said…
Hi Abu-Hafss,
Please refer to the "sequential timer" section in the following pdf link:
Abu-Hafss said…
Hi Swagatam

The link shows monostable timer with manual triggering whereas, I was talking about automatic triggering at power-up.

If for example we have 3 sequential timers:

a) Only the first timer should start at power-on.
b) The first timer should trigger the second.
c) The second should trigger the third.
d) The third should re-trigger the first one.

My problems is how to restrict the 1st timer to be triggered automatically at power-up?

According to my observations, sometimes 1st timer gets triggered, sometimes 2nd, sometimes 3rd, sometimes all three and some times none.
Swagatam said…
Hi Abu-Hafss,

Replace the switch "S" with a 1uF capacitor and also connect a 10k resistor across the positive and pin2 of this IC, now the circuit becomes an automatic sequential timer as soon as it's powered up.
The circuit will always start from IC1 when switched ON as per my simulation, just try it.
kikira said…
Good afternoon sir,
Would U kindly mention the value of D1 & D2.
Wheather a 6v relay will work instead of a buzzer?
Inform the caution to be taken for 6v supply instead of 9v d.c.
Thanks ................
Swagatam said…
Kaushik, D1, D2 are 1N4148 diodes

6V relay can be used but the supply should be also at 6V

the same circuit can be used for 6V operation also, no changes would be required.
kikira said…
Good evening sir,
Wishing you a hearty thanks for your kind reply.......
A request ;
A search option & "go to top" is needed on your web page....... So many useful circuits ...a huge no of posts & comments.....
With regards,
Swagatam said…
Thank you Kaushik,

Your suggestion is very good.

If it's possible to include this feature in my blog template, I will make sure it gets implemented soon.
Swagatam said… the way the search option is already there at the left top of sidebar.
Jomel Calasiao said…
sir, can i use the same circuit above using a 12volts power supply? or do i have to modify some of the parts?
Swagatam said…
Jomel, 12V can be also used for the same circuit, no changes would be required
vipin kumar said…
Hey Swagatam,

I like ur circuit and i am new to electrical world.
So i want to know that if i have an input of 220 volt ac , what value of resistance i must have to add do that i get output of 9 volt ac
Swagatam said…
Thanks Vipin,

If you are referring to the above circuit, for a 220V operation you can use a 12V AC/DC adapter for it.....12V would also work for the above circuits.
Jomel Calasiao said…
sir,i'm planning the same circuit above to control a motor of 12v, 8 amps for a certain time duration,i attached a tip3055 transistor in series with a 1M resistor to the output in place of the buzzer, will that work?
Swagatam said…
Jomel, you will need to do it via a TIP122 transistor.

connect the base of TIP122 to pin3 of the IC via a 1k resistor.

connect the emitter of TIP122 to the base of TIP3055

connect the emitter of TIP3055 to ground.

join the collector of both transistors and connect it to the negative of the motor, and connect the positive of the motor to positive of the supply.
Abu-Hafss said…
Hi Swagatam

TIP122 is a darlington pair, so shouldn't it be replaced with TIP31?

Otherwise, what would this configuration be called i.e. 3 transistors connected in series with common collector?
Swagatam said…
Hi Abu-Hafss,

Here we are looking for a guaranteed and an optimal switching conditions for the 2N3055 since the source current is very low in mA.

Therefore a Darlington is a better choice since it would ensure the full dose of current for the 2N3055 producing an optimal switch-ON for the load
Jomel Calasiao said…
OK,thank you sir,i will try and see what will happen
Jomel Calasiao said…
Sir,may i ask what is the reason behind the additional transistor tip122?
Swagatam said…
Jomel, for 8amp collector load, the base of 2N3055 would require around 200mA current, TIP122 is used for optimally satisfying this amount of current to the base of 2N3055
kikira said…
Good morning sir,
My android mob. is the only way to connect with Net. It's quite tough to search any particular ckt. Plz. Help!!
I need to convert 12v a.c to 12v d.c
A tr. manufacturer told that when a bridge rectifier is added with the out put of 12v d.c it increases the voltage upto 3v. Is it true? Then what should I do....
1)A tr. of 9v d.c out put...
2)any ckt. that provides 12v a.c to 12v d.c using a tr.
Please guide.
With regards, k.kausik
Swagatam said…
Hi Kaushik,

yes that's right. in fact with a filter cap it could rise upto 16V

you can use a 7812 IC for restricting the voltage to 12V or add 4 to 5 rectifier diodes in series with the positive for the same.

the diodes could 1N4007 or 1N5402 depending upon the output current specs
Azam jamal said…
I want to make a circuit which work's like I have 9 25 watt clf bulbs and I want to do that when I switch off the first CLF then after each 5 minutes the remaining light would switch off regularly like each should go off after 5 minutes of other means that in 45 minutes all 9 lights go off respectively.So in this case would the last circuit among the drawing's will work or not.Please help me ?
Swagatam said…
I'll try to design it soon and post it in this blog.
Nipun Gupta said…
Hello Swagatam i wanna ON my Banner Light with 555 Timer IC for particular hours like 6-8 Hours and then i wanna off it automatically. Is it possible? Please help me regarding this. it will be helpful for me.
Swagatam said…
Hello Nipun, a 555 IC circuit may not be suitable for acquiring such long delays due to its inefficiency, a 4060 IC is recommended for this as explained in the following article:

try the second one for your application
EyeWithShy said…
how to increase time duration of this timer? like 4 hours timer
Swagatam said…
by increasing the values of R3/C2
Silence Screams said…
If I changed the voltage to 15V, will the values of other components change? If yes, then what will be their new values?
Swagatam said…
Hello, nothing will need to be changed for 15V, however at 15V the IC can get a bit warm so it's not recommended.
Hello Swagatam, I would like to know if an IRS2453 can be driven by an external oscilator, like UC3845. I want to use this circuit to drive a H bridge in a welding inverter.
Swagatam said…
Hello Alexandru, According to me it does not include this feature, it can be programmed only through the specified Rt/Ct network....
Enrico_Vialli said…
hello sir,

i want to make a bathroom light timer switch with IC555, but i want to add a warning alarm sound before the lights goes off when the time limit is reached, can you help me?
Swagatam said…
Hello Enrico, I can certainly help you, please let me know what type of buzzer and lamp do you intend to use in this application.
Enrico_Vialli said…
buzzer is DC type and lamp is fluorescent type...what im trying to do is to make it give a warning sound(somewhere about 15 seconds) before the timer switch the lamp off.

the timer is adjustable from 1-10 minutes
Swagatam said…
OK I'll try to post it soon...
Tony said…
I am new to electronics but I thing this circuit is ideal to start with. I wish to use the cct on a device. The idea is to set on the buzzer after I set the time sort of a reminder. Does this cct help. Let say I want thw buzzer to sound at 8.00 am, noon and 6.00pm is it possible please.
Swagatam said…
No it won't be possible with this circuit, you will need a 4060 based timer circuit
Tony said…
I tried to find a cct but I not sure if it works properly do you have available on you site
Swagatam said…
you can try the following circuity:

remove D1, otherwise the time delays will not repeat.

The timer will produce OFF/ON delays with equal intervals depending on the values of the P1 and C1.

Amr Osama said…
i want to make a simple timer for a 3hp 220v ac motor to make it on for 30 min and off for 15 min , what circuit should i make?
Amr Osama said…
i want to make a simple timer for a 3hp 220v ac motor to make it on for 30 min and off for 15 min , what circuit should i make?
Swagatam said…
you can try the following circuit:
Amr Osama said…
Thanks a lot ,I will try it :)
John Woodhead said…
Hi Swagatam. I building your simple CDI circuit. which is fine for a single cylinder motorcycle motor. However. I intend to use it on a 2 cylinder V motor. Most of these motors have 2 pick ups, but the motorcycle I have, has only one pick up. This means that it fires on the first cylinder ,but I need to time delay for the second cylinder also using a second CDI. A milli second adjustment would be needed to get the required TDC firing point. Can I configure the above circuit from the pic up for the pulse. Can you help
Swagatam said…
Hi John, are you sure a manual, fixed delay setting would do the job? I don't recommend it...I think it would be much better if you installed a second pick-up coil and a separate CDI for triggering the second engine.

By the way if you think the manual option would be OK, then you could try the following design instead

adjust R2/C2 for the required delay, and remove the relay....the trigger could be extracted from the colector of T2
John Woodhead said…
Hi Swagatam.
Thanks for the time delay switching circuit.Much appreciated. Tomorrow I'm starting trials with the CDI. if I get the spark at both positions at their required TDC points, the timer won't be necessary, but if I'm correct, the time delay will be needed for the second cylinder in the V 2 cyliner motor. As it must fire before the pic up flywheel can do another revolution. Meaning 2 cdi's, one with the time delay the other without. I'll keep you posted.
Just a note. I am also going to add your advance /retard circuit, as well as the the auto select for the advance/retard. To make an intelligent CDI giving optimum performance.
Swagatam said…
You are most welcome John! If your theory is correct then my referred circuit should work with perfect results, however how would you implement it for the proposed function? that appears to be a bit puzzling? Let me know if you need any help regarding this. Wish you all the best!
Abu-Hafss said…
Hi John

Please inform the name/model of your motorcycle.
John Woodhead said…
The bike is a Despirado 400. Not sure but I think the model is around a 98. I can't find A wiring circuit anywhere on the net.Ive tried to buy a new CDI but every place I've got one from are Duds. So I'm building on. The big problem is, it has only one pick up. with the firing at 180 degrees from TDC of the first cylinder to the firing of the second cylinder.Thats about 0.0588 of the second time out needed.This is at Idle speed of 1000 rpm. Take that to 8000 rpm at full revs. I still need the advance and retard. with the time out changing as well to about 0.0167 of a second. The XV4002NT Smart CDI is the correct CDI. I cant afford the new price at R14000.00 The value of the bike is only R35000.00 I've been ripped of twice trying to buy. So if anybody has one. I can afford R2000.00 and only after it's fitted and the bike is running.
Swagatam said…
thanks John, I can design the circuit as per your above specification which will spark the two engines at a given predetermined rate, and that won't cost you more than Rs.800/-....the design might include two identical CDI sets and a sequential timer circuit
77FALLEN2 said…
I need to make a simple timer circuit that only turns on an led for an adjustable amount of time between 10-60sec then turns off for 5-20min. ther will be a sensor or switch used to cycle the circuit on/off. When the switch is closed and the power is restored to the timer circuit, the led will need to be powered on then count down to the off state. This will need to either run on a 3 or 6v battery source. I am not sure if This should be a 555 or 556 timer or 4060 as in your other programmable timer circuit. The accuracy of the timer is not critical but it needs to be reliable. I do have a 556 timer already. Your help would be appreciated. Thank you.
77FALLEN2 said…
Hello, I need help designing a circuit that's adjustable and only turns on an led for 10-60sec and turns off for 5-20min. It will run on 3v or 6v battery and I will use a sensor or switch to power up the circuit. When the circuit gets powered up, the beginning state of the led must be "on" and then begin the timer function to turn "off" then remain off until the next timer is complete then it repeats. The accuracy is not critical but should be fairly accurate and reliable. I though of using a 556 timer which is a double 555 timer or possible using 4060's. Thank you for your help.
Swagatam said…
you can try using a couple of 555 iCs or through a couple IC 4060 as shown in the following article

for getting an initial LED ON connect it across the N/C of the relay and not N/O

if you don't want the relay, the top BC547 can be replaced with a PNP, and the LeD connected across its collector and ground.
77FALLEN2 said…
Thank you for your reply. I will base my circuit on the 2 4060 design in the link you provided. What is the equivilant PNP transistor to use since I will not be using a relay? Also, can I use 100k micro trim pots to adjust timers? My local Radio Shack has limited supply of components, the .1uF capacitor is a ceramic disc and the 1uF is a tantalum, will these work ok? I will be building this circuit as soon as i can locate all the components, I really appreciate your expertise. Is there any chance you can draw a schematic for me with with PNP transistor rather than relay and eliminate the red/green status LED's?
Swagatam said…
the 1uF should be a non-polar capacitor so tantalum will not do since it could be a polarized cap.

the PNP spec will depend on the load, if it's below 200mA, a 2N2907 will do, if it's below 50mA, then a BC557 will do.
Swagatam said…
make sure to put a series limiting resistor with your LED
hi sir , i am disturbing you again with my small doubted and mistakes, from your suggestion i got idea regarding the led drive circuit and it working fine,
and now need a timer function, when i switch on a device i need delay to operate protect my device,only after few second i want to switch on the device , please give me suggestion
Swagatam said…
Thanks Asainar,

you can use the following concept for your requirement:

you can include the relay for controlling the LED delay time or simply remove the relay and connect the LED with the collector of the PNP transistor, but in that case make sure that the PNP is rated appropriately to handle the LeD current.

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