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Electronics 5 Second Timer

Discussion in 'Modding' started by Gambler, 9 Jun 2007.

  1. Gambler

    Gambler What's a Dremel?

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    Hey all!

    I'm a complete electronics newbie, but I still try!

    Anyway, I need a little help. I want to put together a timer that works like this:

    1. I close a switch
    2. A timer delays 5 seconds
    3. A second circuit closes after the 5 seconds.

    I looked at the schmitt trigger, but I cant figure out how to put everything together.

    Thanks!
     
  2. ChromeX

    ChromeX Minimodder

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    So just to clarify, you close the switch on the timer, wait five seconds, then the other circuit switches on?
     
  3. Gambler

    Gambler What's a Dremel?

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    Yep, the main goal is to put lag in the button. Push...wait...ah... Releasing the switch can (and would be best) turn everything off.
     
    Last edited: 10 Jun 2007
  4. cpemma

    cpemma Ecky thump

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  5. Gambler

    Gambler What's a Dremel?

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    I warned you that I was an electronics newbie. I know that pin 3 is often used on a 555 for the oscillation, so I am assuming that is is the "Output" that is referred to. But...is the output negative or positive?

    What is a common capacitor-resistor combination that I could most likely steal off some old projects?

    http://555-timer.clarkson-uk.com/operation/mono2.gif

    Thanks!

    Please do NOT hotlink to sites without their permission
     
    Last edited by a moderator: 10 Jun 2007
  6. ChromeX

    ChromeX Minimodder

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    The output will be low until the 5 seconds has passed then the output will switch high. Try look for 220 uF 20.66 K or 470 uF 9.67 K they seem to be fairly common.
     
  7. cpemma

    cpemma Ecky thump

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    There's a calculator on the page, input '5 secs' and he gives you a list. You can round the resistors off to the nearest standard value, so 220uF & 20k is one combination, 100uF and 47k is another. There's no point in being too exact on the resistor when a capacitor tolerance is +/-20%; if you want 5.00 seconds use a variable resistor and tweak.

    For what you say you want,
    the 555 output from pin#3 can be used to operate a relay to give power to the second circuit.

    [​IMG]

    If the relay isn't a low-power-coiled one you'll need a transistor switch on the 555, there are thousands of examples out there.
     
    Last edited: 10 Jun 2007
  8. Gambler

    Gambler What's a Dremel?

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    [​IMG]

    Isn't this just a schmitt trigger though? If I am going that way could I use the 74HC14 and accomplish the same thing? I've looked at using the 74HC14, but I figured using a 555 would be a lot simpler, I guess not...

    Thanks
     
  9. cpemma

    cpemma Ecky thump

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    You could make a crude delay with a Schmitt inverter, but you'll still need R1, C1, D2 and C3, plus you'll definitely need a transistor switch and its base resistor for current boost, so no simpler, less accurate, bigger footprint, higher cost.

    If crude will do, just delay a transistor switch-on.

    [​IMG]
     
    Last edited: 10 Jun 2007
  10. elctroJunky

    elctroJunky What's a Dremel?

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    The circuits shown here are both simple and reliable, so my post is just another way of doing it.
    You could also use a minimal microcontroller circuit(there are microcontrollers the size of a 555).
    This suggestion is more like an overkill for a simple timer circuit, but it could be a nice and simple start to get into microcontrollers(if you ever planned on doing that).
     
  11. Gambler

    Gambler What's a Dremel?

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    The only reason I ask about doing it with a schmitt, is that you can use smaller capcitors. I dont have anything about about 100uF, nor do I have (or can get within a week, im impatient) 10,000 Ohm resistors.

    There is no small way of doing this? A 470uF with 10,000 Ohms is going to be a fair sized capcitor. My 10uF are about as big as I can accommodate (size wise).
     
  12. unclebulgaria

    unclebulgaria What's a Dremel?

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    elctroJunky > Have a look at the ST7FLITEUS series, much, much, much smaller than a 555!
     
  13. Meblin

    Meblin Supposed IR God!

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    Sorry to piggy back onto this discussion but the new site layout is slowing my search down :wallbash: It's been a while since I last visited

    I want to create a similar timer that will turn off after 2 hours or so. I would like to use a switch to start the timer (then it would be inactive until it is re-pushed). I would prefer to have no power consumption until the button is pushed again.

    This timer would be used to turn power on to a charger and then cut the power after the alloted time.

    Hope this makes sense.

    Meblin
     
  14. cpemma

    cpemma Ecky thump

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    "no power consumption" means build it round an hour-glass or two ;), but you'll get very low power consumption from a CMOS 555 monostable plus MOSFET switcher, and I think it will handle a few hours delay with a low-leakage timing capacitor.

    Another way to get long delays is with a CMOS4060 chip, built-in oscillator and divide its frequency by 16384 to create a very slow astable; you'll need a system to stop it coming on again after 4 hours.
     

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