How do I build a time delay circuit (novice)

Discussion in 'General Electronics Chat' started by snipershot, Sep 27, 2010.

  1. snipershot

    Thread Starter New Member

    Sep 27, 2010
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    Hi. I need to figure out how to build a time delay circuit or where to buy them cheaply. I need one as i have an idea for a cheap airsoft grenade. the basic idea is some LED's in parallel connected to a 9volt battery as well as a small speaker. This is the connected to a simple switch which when activated waits 4 seconds the turns all the LED's on and emits a noise.( If possible i want this to turn off after a few seconds but it is not necessary) If it cant automatically turn off easily then they stay on until the switch is turned off.

    The reason i want this is i want to make a grenade for airsoft that isnt explosive due to law in my country and so isnt dangerous. and isnt extremely expensive. I plan to place the circuit inside a ball of some kind so it can be thrown and isnt going to badly hurt anyone it lands on.

    I plan to have approximately 10-15 LED's, speaker 9v battery. switch and the time delay. if this works i will have a cheaper grenade that is safe and works at night. Any help is greatly appreciated.


    Just a note. This is not for school or anything so im not required to do this work myself. It is simply something i am thinking of doing.
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
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    On google search about "555 timer circuits".555 is a very cheap IC and good for this kind of jobs.

    Good Luck
     
  3. snipershot

    Thread Starter New Member

    Sep 27, 2010
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    I have looked at these but i know next to almost nothing about circuits apart from basic stuff so most of what those show is beyond me. Plus it it sounded like the current goes through for a few seconds then it wait a few seconds and turns off. I dont want this. I want the LED's to stay on but the speaker/siren to stop. I thought I could do this with a fuse that will only last 2 seconds of 9v but dont know how. Hence the asking. If google could answer it basically i would have it finished.
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    There are a number of ways to hook up a 555 timer and the e-book (links at the top of the main forum pages) has an entire chapter on LED flashing circuits, adding sound is no big deal either.

    As to having limited electronic knowledge you're going to have to learn the basics of reading schematics and the basics of construction - that or find a friend that knows how. as I doubt anything commercially pre-made for this exists.
     
  5. mbohuntr

    Active Member

    Apr 6, 2009
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    Snipershot; Marshallf3 is correct. There are probably dozens of ways to accomplish this, but without some electronics basics, It will be very difficult. I am in the process of building a similar circuit that delays a pulse from a 555. You could take the output and power the sound by the pulse, and the lights from a R-S latch driven by the pulse. The latch stays on until you manually turn it off. I think a much simpler approach is to look into PICAXE microcontrollers. They are supposed to be very inexpensive, and easy to learn. The 08's are a couple of bucks, and the programmer is around thirty. They plug into your laptop, and the language is supposed to be very simple. I am going to use them myself after I burn out my brain using traditional electronic components. :p
     
    Last edited: Sep 27, 2010
  6. Wendy

    Moderator

    Mar 24, 2008
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  7. snipershot

    Thread Starter New Member

    Sep 27, 2010
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    Thanks guys. I have a basic level of electrical circuitry and can build a circuit if i have the diagram and all the parts but when people start talking about electolyte resitors and stuff i am clueless. I will read the stuff in those links and see if it tells me what i need. Thanks for the help.
     
  8. snipershot

    Thread Starter New Member

    Sep 27, 2010
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    OK. I feel like such an idiot. I have had this learn electronics thing in my room for about 5 years. i just went to go look at the books in it and look at the parts list and found that apart from 2 resistors and the circuit board i have everything. So i can now make sense fo the diagrams and instruction ppl have given me thank you very much.

    Something else i want to know. If im running a 9v battery with this. What fuse do i need so that the fuse will blow after 2 seconds. I want this as the speaker needs to turn off bt the lights need to stay on. But i dont want it reusable until something has been changed other wise the enemy in the game can just throw it straight back after rearming it and a fuse that needs to be changed seems the simplest way. if thewre is an easier way for about the same price then please tell me. if not then what sort of fuse do i need.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    They practically don't exist anymore, but I loved the old flashbulbs. They were perfect for this kind of stuff.
     
  10. mbohuntr

    Active Member

    Apr 6, 2009
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    What about a key switch?
     
  11. snipershot

    Thread Starter New Member

    Sep 27, 2010
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    I was planning to use just a regular switch with 3 pins.

    So If im reading this right i wont be able to find a fuse that will blow when connected to a 9v battery. hmm. Anyone know how i get the siren to turn off but not the LED's. is there some sort of timing switch i could use thst flicks itself off after a set time?
     
  12. mbohuntr

    Active Member

    Apr 6, 2009
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    That is what the S-R latch is for, The same pulse that sets off the siren, trips the S-R latch. The Latch keeps the lights on until it is reset(along with the timer. ) Look up the 555 circuits that were suggested, then the S-R latch. Play-hookey is an excellent sister site to this great site for learning the basics. The delay in the pulse will be a capacitor/resistor discharge circuit on the trigger of the 555. Search for capacitor charge/discharge rates. This stuff ought to keep you busy for a while and get your ideas flowing. Pick up a breadboard, and some LED's, resistors, 555's and caps (electrolytic caps)10-100uf and jumper wire at radio shack. A 9v battery will work as well. Time to learn and have fun...
     
    Last edited: Sep 29, 2010
  13. lmartinez

    Active Member

    Mar 8, 2009
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    As novice, an RC circuit is the way to go....
    Browse around the internet.....:cool:


     
  14. mbohuntr

    Active Member

    Apr 6, 2009
    413
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    Here is a couple of links to get you started. Don't get too bunched up by the math, the concepts are more important to get your thoughts flowing. The RC charge/discharge cycle is what controls the pulse/s of the 555. A(monostable multivibrator) simply means one pulse. An (astable multivibrator) simply gives a continuous train of pulses. Someone must have thought a complicated name was important...:rolleyes:
    R/C circuits
    http://www.allaboutcircuits.com/vol_6/chpt_3/17.html
    http://academic.reed.edu/physics/courses/phys100/Lab%20Manuals/RC%20circuits/RC.Circuits.pdf
    555'S and S-R
    http://forum.allaboutcircuits.com/blog.php?b=190
    http://www.talkingelectronics.com/projects/555/Page1-555.html
    http://www.allaboutcircuits.com/vol_4/chpt_10/2.html

    http://www.play-hookey.com/digital/rs_nor_latch.html

    I am going to try the Nor latch myself because it doesn't require a clock pulse like a standard S-R does.

    Happy reading
     
  15. mbohuntr

    Active Member

    Apr 6, 2009
    413
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    One more thought... you could use a 556 (2 555's in one chip) and the first is monostable for the blast, and the second is astable for flashing the red leds until you shut it off. The key switch prevents opponents from re-using it.

    _____/----------\______ blast

    _____/--\__/--\__/--\__/--\__/--\ continuous red light pulses
     
  16. snipershot

    Thread Starter New Member

    Sep 27, 2010
    6
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    that sounds plausable. but i released a totally budget way is to have the switch spring loaded with a pin so once its pulled the switch activates and with out the pin you cant turn it off. then ill figure out a way in which you open it and then insert the new pin. Ive actually gota mate who is good with electronics and isgoing to program the 555 and build a prototype then once i kno what to do ill make as many as i can. thanks for the help guys.
     
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