Delay Timer




Introduction: Delay Timer

This is a delay timer using a simple 555 timer. that will keep a eg. fan, light, motor running for a preset period after a designated trigger is activated. (e.g keeps your computer CPU fan running for another 5 minutes to cool after pc is off)

Go easy on me this is my first tute:P

Disclaimer: i take no responsibility for any issues you may encounter using this product.

there prob wont be any but just covering my ass:P

Step 1: Components and Pcb

2 pin terminal block *3
Capacitor (ceramic preferable) = 10nf
Electrolytic capacitor 220uf = 16v
1N4001 diode
555 Timer
IC socket (8pin)
N-channel MOSFET(varies according to job)
Resistor = 33k
Resistor = 10k
Resistor = 100k
Resistor = 1k
Resistor = 51R
Potentiometer (PCB mount) = 1M

PCB of course or breadboard if you wish to test first
be aware if you wish to have the output hooked up to a motor you may need different fets to the one listed and also may need another diode to protect it, DC computer fans dont have current spike problems. feel free to ask me any questions and ill do my best to answer them for you.

Its up to you of which method you pick to get your circuit, i have used a photoexposure process and a veroboard, both work ok, the veroboard was more compact but it was messy and dirty.

Step 2: Circuit

I designed and created this circuit myself it is setup for turning off a fan after 6 minutes when the computer turns off but this can be changed if you moddify the NC and the NO pins on the relay. It should run from about 1:20sec - 6min. i realised later there waere 2 fauls, 1 due to the relay, i have discoverd that the relay is very tempremntal, when the relays power is switched off the capacitor side of the relay (common) must hit the NC (normaly closed) before the other side closes otherwise it will not begin to time and will simply switch off, i solved this problem on mine by removing the cover of the relay and bending the NC pin so it was closer to the common. The other issue was that if the trigger was switched back on druing the countdown the timing would just pause and resume as soon as the trigger was activated meaning depending on how long it had been running it would varie the remaining time.

Note: the motor can be replaced by a relay (with a diode) so this can control anything you wish,such as a delay for your car headlights or a bathroom fans to remove steam after you leave, again it is a very vercitile circuit and can be used for a variety of things.

"The PCB artwork below is mirrored for direct exposure to a PCB"

Step 3: Testing

i origionaly tested this on a breadboard before moving it to a PCB but if your confident go ahead. the test below was my origional prototype using the veroboard, the multimeter is reading in Amps (0.67A) of how much the watercooling kit drew, but the relay draws nothign so you should be able to run it off almost anythign (you can replace the trigger DPDT relay with a lower voltage one or even use a IC sized relay as the circuit drawn very little current. (next version for me will be with a IC sized relay or a reed relay).

The video is the prototype on my cold cathodes. i clicked the multipul times to show that the relay was clicking and it didnt disrupt the circuit.

Step 4: Final Product

the final product is the lower PCB, it works perfectly and as planed, i shrunk it down to save space so i could place in a housing. I did this as a school systems project so its not quite complete yet but i will update when necessary.

any questions and ill try my best to help, was my first tute so would have missed things for sure. email me at or through my instructables mail. and make subject like TURBO TIMER HELP or somthing similar
hope works as well for you as is did for me.



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    14 Discussions

    hi you there, what is the value of the transistor? you did not mentoin it.


    ohhhhh and I need it to be ran from a motion sensor cant figure out how to change this from AC to DC (from basic 110 V motion sensor)

    ok I'm not to wise when it comes to this ,,but ,, I need to make a 555 timer with a delay and a reverse to change polarity , I am making a prop i used a drill and have it rewired to go to my 12 V batt. i have the start , stop covered I think , I just need to know what resistor (s) I need and what (relay(s) to do this.
    so over all I need this to run a cycle of about 1 to 2 sec. then pause for about 10 sec then reverse ,and reset. so start ,stop, delay ,reverse ,reset is wut i need it to do can anyone help with this??

    cool do you have any other detinater timers that use risitors

    what was the numbr of dat resistor 51R..  wats dat??an ohms??rply plz.

    1 reply

    51R means 51 ohm, yes; this is the standard in electronics; M-mega (10^6), k-kilo (10^3), R-just ohms (multiplied by 10^0 = 1)

     dude,, is this timer must be use in any appliances?? for example the television is on then the brown out came,. if I put that delay timer on t.v, is it possible?? reply asap..plz.. 

    Hi thanks, but how if i just need for 5-10 seconds delay for led project? any suggestion?

    itx nice..!

    can yew tell meh the formation of pulsating dc using 555 timer ic?

    Hi, I'm an old guy and I used to make up circuits and such, I've not done this for many years but I suddenly decided to do it again as a hobby, I used to make a 555 dummy alarm, they run on a 1,5 V nicad which lasted for many months, I can't remember the components other than:- 555, CAP,LED and I don't remember. PLEASE CAN ANYONE HELP ME WITH THE CIRCUIT. THANK YOU

    Nice project! I will like to make a timer for a hydroponic system that switches on for one minute, and four minute off. Is it possible to run 120V ac with this?

    Neat I've been looking for instructions on how to do this for a while. Just an idea but couldn't you take a kitchen timer and just solder the speaker leads to the object to use it as a timed switch?

    can you change the time limit and can you use it for other things like leaving a room and making the light turn off 3 minutes after you leave?