Adjustable Timer Circuits Using IC 555

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

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.

 

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

A circuit design requested by Mr.Bourgeoisie:

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.

133 Replies to “Adjustable Timer Circuits Using IC 555”

  1. Anonymous

    Hi sir, very useful article. Question from me can this circuit control the ac synch motor?. I try to find a circuit that can be use to control ac synch motor direction forward and reverse with time period. please guide me? my email asnf.adsblogger@gmail.com

    Reply
  2. Bourgeoisie

    Hey Swagatam,

    I want to build a power outage & resumption alarm circuit with the IC 555 that would sound for a given period of time and then goes off on its own. Any suggestions?

    Reply
    1. Swagatam Post author

      Hey Bourgeoisie,

      The circuit looks a bit complex because it requires triggering during both the occasions.
      I'm trying to figure it out, will post it here when I finish designing it.

      Reply
    1. Swagatam Post author

      Bourgeoisie, just add a 1000uF/25V capacitor in series between the N/O, N/C relay contacts and the positives of the IC 555. It means the current from the relay should pass through the 1000uF capacitor for reaching the pin 4/8 of the relevant 555 ICs. The positive of the capacitors will go to the relay contacts while the negative will go toward the ICs.
      Also make sure that you add a 220K resistor across each of the capacitors.

      Regards.

      Reply
  3. Bourgeoisie

    Hey Swagatam,

    Very cool solution, i tried it out and it worked; but i have a few challenges & questions.

    *The way i understand the solution to be is that, the capacitors charge up and become open circuits(D.C voltage) and the 220K resistors don't allow sufficient current to get to the IC.(Please clarify this)
    ->But if the relay latch goes from NC->NO->NC(power loss and resumption within a short period), the alarm dosen't go off, because the 220K resistor dosen't bleed the capacitor fast enough i guess. When i used 470ohms, the response was faster. So so i go with 470ohms and 1000V? or do you have a more efficient solution.
    ->Do the values of the capacitor and resistor form the time constant(RC)? and how do i set the alarm sound time?

    Thanks.

    Reply
    1. Swagatam Post author

      Hey Bourgeoisie,

      The earlier solution was not so good, I have designed another circuit which is perfectly suited for the purpose.
      I have posted the circuit above, however you will have to connect a buzzer at the output, a speaker will not sound as the IC is not configured as an oscillator.
      R3, C1 may be adjusted for getting the desired ON time delay.
      Please check it how it works.

      Regards.

      Regards.

      Reply
    2. Bourgeoisie

      Hey Swagatam,

      Thanks for the circuit, but when i put it together it dint work. I connected the positive 12V D.C supply to the top left 0.1microFarad capacitor and a 240 ohm buzzer to the pin #3 output. Please help, i cant seem to figure out what i'm doing wrong.

      Thanks.

      Reply
    3. Swagatam Post author

      Hey Bourgeoisie,

      Check the circuit separately first.
      Power the circuit and then momentarily short the C1 points manually.
      The buzzer should sound and remain ON for sometime and then switch OFf.
      I think you will have to increase the value of C1 to make it function properly.

      Regards.

      Reply
  4. Bourgeosie

    Hey Swagatam,

    The voltage at the positive and pin #3 in the circuit are the same, and no current flows through the buzzer, but when i connected the buzzer to pin #3 and ground, the buzzer came on but dint go off after the (R3C1) set time. How do i then go about it?

    Regards.

    Regards.

    Reply
    1. Swagatam Post author

      Hey Bourgeoisie,

      I have updated the above circuit, please check it.
      This time it should definitely work because I've tested this circuit.

      Regards.

      Reply
  5. Bourgeoisie

    Hey Swagatam,

    Just to be clear, is the 10k resistor connected to the 1000microFarad capcitor only or is it connected to the 1000microFarad and the line going to pin #2?Secondly,the 1000microFarad capacitor and which of the resistors form the external timing components?

    Reply
    1. Swagatam Post author

      The 10K connects to 1000uF (pin #6 and 7) and not to pin #2.

      The 1M pot, 10K and the 1000uF cap form the timing components.

      Are you having problems? This circuit should work without fail.

      Regards.

      Reply
  6. Anonymous

    Hi, I have a problem in using PNP transistor, using a 555 IC powered by 12v i connected 2.7k resistor at pin 3 and connected the other end to Base of PNP (557( and connected 12v to emitter and connected the collector to a relay and grounded the other end of the relay and also connected a diode on the two pins of relay. though the IC 555 is working properly and pin 3 goes to ) after the set time the PNP transistor is not working. i also tried BD140. can you help

    Reply
    1. Swagatam Post author

      connect an LED in series with the BC557 base resistor (pin#3), it will give you an clear indication of all the functioning. If the LED responds, but the transistor does not respond would mean either the transistor is faulty, wrongly connected.

      Reply
    2. Anonymous

      Yes, i had connected an LED to the ground through a 2.7k resistor to indicate output of pin 3, it is working fine. BC557 pin out, flat side facing our face, pin1-E emitter, pin2-B Base, pin3-C, Collector.

      should i need to connect a resistor from +volt to Emitter as pullup resistor?.

      Reply
    3. Swagatam Post author

      what is pin1? right side or left side pin?

      facing the print toward us, and the pins downward, the right pin is the emitter, left is the collector and the center is the base.

      no pull up resistor is required, 555 can supply as high as 200mA…

      Reply
    1. Anonymous

      thanks, i have one more request, NPN transistors are easy to configure in a circuit, however PNP is difficult, can you help in understanding them better

      Reply
  7. Anonymous

    Hello mate,
    Could you tell me a rough aproximation of the maximum delay this circuit can offer? Which set up should i use to achive it
    Thank You!

    Reply
    1. Swagatam Post author

      Hi,

      Technically you can get infinite range of delay from this circuit, but the circuit starts drifting and doesn't give accurate timing with ranges beyond 2 hour.

      Reply
  8. Shiva Kumaren

    hai swagatam i want timer circuit without trigging it ,i want to give supply 12 v through another low voltage cutoff circuit relay ,so that if it receives 12 volt supply it should delay on in 15 seconds so that it can reduce unnecessary cutoff of sudden voltage fluctuations .

    Reply
  9. Anonymous

    Hi Swagatam, i wanted to try out the design above. but is it possible to hv 2 switches on the circuit? i wanted to make the circuit works by either push on both switches or either one of them. another ques is, hw am I going to select the correct resistor & capacitor to determine the time I want? for eg: 15 mins, 30 mins, 60 mins & 120 mins. Lastly, will the buzzer kept on beeping when the time is up until we switch it off? thx

    Reply
    1. Swagatam Post author

      I did not understand your requirement,

      You want two switches for the same actions?? you may just connect another switch parallel to the shown one.

      Timing can be set by adjusting the values of R3 and C2

      yes once the time lapses, the buzzer would keep buzzing until the power is switched off or the push button is reset

      Reply
    2. Anonymous

      sorry, not going to use 2 switches anymore. Hmm, is there any formula to find out the time interval? and does 555 produces accurate timing?

      Reply
    3. Swagatam Post author

      You can use an online 555 calculator, just fill the given slots and get the required results.

      for smaller time periods it gives reasonably accurate timings, but for longer duration it tends to drift away a lot….

      Reply
  10. Anonymous

    one problem sir, hw long can does circuit last? possible for a month? if no, any other suggestion to do a timer circuit which cn last tat long? tq

    Reply
  11. Bibin Edmond

    Hi Swagatam,

    I need a timer circuit for my pc fan… ! with 5 min interval,
    ie: The fan should turn on automatically after 5min and should stay on for another 5min and again should turn off after that..

    on time : 5min
    off time : 5min

    12v dc fan..

    please help me to find a circuit with 555 or cd4060.

    thanks

    Regards,

    Bibin edmond

    Reply
  12. Mahmoud Al-Ashi

    hey sir, i am designing a water level detector circuit. when the water level reaches to the max, i want a buzzer to turn on ONLY once for like a second and it will stop a motor. can this be done using this circuit? if yes please explain. if no please give some hints. thanks in advance

    Reply
  13. Anonymous

    good day mr. swagatam. can you please help us construct a timing circuit which is an output of a logic circuit. we want it to have 3 different time duration outputs. hope you can help us. thanks.

    Reply
  14. rajav2

    I came across your website searching for a solution to my problem.
    Hopefully you can give some insights on how to do this.

    I am doing a mod for the multi effects Zoom G3X.
    Basically converting some of the buttons into external foot switches.

    I got a situation where to trigger a function I must do the following
    – Hold down a button then press another button to trigger the feature.

    When I tried it with a 3PDT switch it is very inconsistent due to both circuits are triggered simultaneously using a single switch.

    Current situation
    1) Press the 3PDT switch
    2) Circuit A is connected
    3) Circuit B is connected at the same time.

    This results in very inconsistent behavior as circuit A need to be closed first before circuit B,

    I need a way to introduce some delay
    1) Press the switch
    2) Circuit A is connected
    3) Circuit B is connected 100ms later.

    Can you please help on how to achieve this as simple as possible?
    Timing is not critical
    There is no load on the circuit just a simple switch.

    Thanks in advance

    Reply
  15. Anonymous

    Please sir, can i create a circuit that will take 30 seconds to switch On an electric motor with Ic 555

    Reply
  16. Anonymous

    Hello swagatam, I am trying to think of a circuit were it has a constant 12~14v supply but a timed output to between the hours of 6 in the morning til 6 at night and to be repeated everyday.the output is to latch a twelve volt relay. Any ideas would b grateful as a I am struggling as a beginner. Thanks

    Reply
  17. jaejjii

    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??

    Reply
  18. jaejjii

    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??

    Reply
    1. Swagatam Post author

      Hello Jaejjii,

      I don't think the simulator would be able to simulate your muscle simulator response along with the above circuit….so I think you should test the configuration practically.

      Reply
  19. nitin rajpoot

    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

    Reply
    1. Swagatam Post author

      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.

      Reply
  20. Anonymous

    Hi sir

    Thanks for the circuit. Can u help me sir? I intended to build a circuit that power ON a hair dryer for 2-10 minutes when switch is closed and power OFF after that period. In between, if I want to OFF the working hair dryer within that period, I intended to put RESET button so. So basically I am trying to make an automatic shut off relay timer with reset button. Can u suggest me any circuit? Thank u in advance 🙂

    Reply
    1. Swagatam Post author

      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.

      Reply
  21. Abu-Hafss

    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?

    Reply
    1. Swagatam Post author

      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…..

      Reply
  22. Anonymous

    great guru am here again the last time i told you that i need a circuit that can close a relay for 8sec and delay it for 1hourand should continue like that for 12hours and stop, you told me to check one of the post you made which i did but to tell you the truth am having difficulties with the designing and time is not really on my side for my project in school. please can you help me design this circuit please i really need your help on this to finish my project please this my email xdungs@gmail.com

    Reply
    1. Swagatam Post author

      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.

      Reply
  23. Abu-Hafss

    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.

    Reply
    1. Abu-Hafss

      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.

      Reply
    2. Swagatam Post author

      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.

      Reply
  24. kikira

    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 …………….
    k.kausik

    Reply
    1. Swagatam Post author

      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.

      Reply
  25. kikira

    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,
    K.Kausik

    Reply
    1. Swagatam Post author

      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.

      Reply
  26. vipin kumar

    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

    Reply
    1. Swagatam Post author

      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.

      Reply
  27. Jomel Calasiao

    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?

    Reply
    1. Swagatam Post author

      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.

      Reply
    2. Abu-Hafss

      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?

      Reply
    3. Swagatam Post author

      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

      Reply
    1. Swagatam Post author

      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

      Reply
  28. kikira

    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

    Reply
    1. Swagatam Post author

      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

      Reply
  29. Azam jamal

    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 ?

    Reply
  30. Nipun Gupta

    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.

    Reply
  31. Enrico_Vialli

    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?

    Reply
    1. Enrico_Vialli

      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

      Reply
  32. Tony

    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.

    Reply
  33. John Woodhead

    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

    Reply
    1. Swagatam Post author

      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

      http://www.homemade-circuits.com/2013/02/make-this-simple-delay-on-circuit.html

      adjust R2/C2 for the required delay, and remove the relay….the trigger could be extracted from the colector of T2

      Reply
  34. John Woodhead

    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.

    Reply
    1. Swagatam Post author

      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!

      Reply
  35. John Woodhead

    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.

    Reply
    1. Swagatam Post author

      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

      Reply
  36. 77FALLEN2

    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.

    Reply
  37. 77FALLEN2

    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.

    Reply
    1. 77FALLEN2

      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?

      Reply
    2. Swagatam Post author

      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.

      Reply
  38. Asainar Vadakkethil

    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

    Reply

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