Circuit with time delay

Discussion in 'The Projects Forum' started by alpha5rose, Apr 15, 2010.

  1. alpha5rose

    Thread Starter New Member

    Apr 15, 2010
    I have a project for school and could use some advice on where to start -

    I must build or develop device that will operate for exactly 14 sec after being started. At the end of 14 sec, the device must either turn on a small light bulb or ring a bell. After the initial run, I will have to change the time interval by plus or minus 3 seconds.

    What's allowed:
    homemade electrical devices
    stored potential energy in form of springs, rubber bands
    gravitational potential energy
    batteries for lighting bulb or ringing bell
    windup toys not initially designed for specific time intervals
    pendulums of our own design

    What's not allowed:
    commercial electronic timing devices
    commercial clocks
    any 110volt operated devices
    any device that will not sit on top of tables
    no chemical reactions
    any device that has no circuitry used to light bulb/ring bell

    I have no problem creating a circuit to light a light bulb, but wondering on how to achieve time delay without timing device. Thoughts???

    Thank you!
  2. roltex_rohit123


    Jan 1, 2010
    Hmm.. thats great. so you dont want to use electronic timers. NE555 would have been the best. anyways do one thing. get a scrap wound uo spring alarm clock. the alarm goes exactly 1 min or half min. confirm it first. there is a mechanism to increase or decrease the speed of that clock study it. get your device assembled as it is and adjust the speed. you can get from 1 sec to any amount you want.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    Dropping a weight at a controlled rate onto a microswitch. Easy to change the weight and also the time.
  4. Markd77

    Senior Member

    Sep 7, 2009
    How close to 14 seconds does it have to be? +/- 0.5 seconds? Exactly 14 seconds is not possible without an atomic clock and even then I'm not sure.
  5. BMorse

    AAC Fanatic!

    Sep 26, 2009
    I would second Beenthere's suggestion, this would be the simplest way to achieve timing. Your "timing" devices could be small bags of sand, that is slowly let out (similar to an hour glass) by changing the amount of sand in each bag you can decrease increase the time delay.... of course you will have to play around with it a bit and see what rate the sand needs to flow out and how much sand would be required to get a 14 second, +/- 3 second time delays...

    B. Morse
  6. Wendy


    Mar 24, 2008
    A simple 555 monostable would do it, if you are asking for what I think you are asking.

    This falls under the homemade electrical devices.

    Bill's Index

    555 Monostable

    Of course, you have to adjust it yourself. Or make something that will more a simple pot to make the timing change.
  7. BMorse

    AAC Fanatic!

    Sep 26, 2009

    wouldn't that fall under the "commercial electronic timing devices" category?? since it is a commercially available timer IC.

    B. Morse
  8. alpha5rose

    Thread Starter New Member

    Apr 15, 2010
    Thanks for the ideas. I do have to agree that the 555 would be considered a commercial timing device so have to go down a different path. That would definitely be the easiest but not within the confines of this project.

    I like the ideas of a weight or sand dropping onto the mechanism/switch to serve as the delay. I wasn't even thinking in those directions. If anyone else has ideas.... the more the merrier.

    Thank you all
  9. retched

    AAC Fanatic!

    Dec 5, 2009
    Ancient engineers used water often as a timer. Unlike sand, water flows at the same rate over and over.. Unlike water, sand doesn't evaporate which could cause long term problems..

    You should look up 'water clock' to see some elaborate designs using water for timekeeping.
  10. ixisuprflyixi

    Active Member

    Sep 16, 2007
    I know its not used often because it is somewhat imprecise but a simple RC circuit to achieve a time delay is very simple. A potentiometer is connected to positive voltage (doesnt really matter what voltage lets say 12V) through a momentary switch and a capacitor of some value is connected between the wiper end of the pot and ground then connect the junction between the cap and the pot to the base of a NPN transistor. simply adjust the pot to achieve your intended delay. I use the RC time constant all the time in simple timing circuits, where super-precise timing is not needed. Hope that helps. then simply readjust the pot to get the +/-3 seconds of delay again.
    Last edited: Apr 15, 2010