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Homework Help: How to turn on & off an LED continously for 1 second?

  1. May 17, 2012 #1
    Please help me the simplest possible way to turn on & off an LED continously for 1 second.
    Please don't suggest me to get it done by micro-controller, help me achieve my goal by the most possible and easiest way.
     
  2. jcsd
  3. May 17, 2012 #2
    Maybe you should hook up the LED to a sinusoid voltage source. Turn the voltage source on for 1 second then turn it off.
     
  4. May 19, 2012 #3

    NascentOxygen

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    Staff: Mentor

    Hi netfreak! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    Usable over a range of DC voltages and currents, the NE555 timer IC can drive a LED with a square wave.
     
    Last edited by a moderator: May 6, 2017
  5. May 19, 2012 #4
    @roshanbbq , no no using AC wont be a good option at all


    Yes I have just bought 555 IC timer and will try using it tomorrow. . .
    For now I was just wondering that by using simple RC circuit, is there anyway I can continously blink the LED on and off for 1 second? I can't get any way to make it work but can you people please help?
     
  6. May 19, 2012 #5

    gneill

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    Staff: Mentor

    No, a simple RC circuit, without other "active" components, is unable to do much other than charge or discharge the capacitor once and once only. You need something that will provide a bit of logic and switching, such as the 555.

    It's not clear why you want to accomplish this task, but I will point out that it is possible to purchase LED's with a built-in circuit that makes them blink at a rate of a few flashes per second. A suitable web search will find them. Good luck!
     
  7. May 20, 2012 #6
    um ok ok , now am getting lil step by step now. . .

    And yes I have got that LED as well that has builtin circuit which makes it flash every second but I just wanted to achieve the same using RC or using inductor alongwith it and simple components like this

    Many thanks to all of you for guiding me so much :) Today I'll try achieving the task by using 555 IC :)
     
  8. May 20, 2012 #7
    Hi Bud,

    Use the 555 timer circuit attached and this website for resistor and capacitor values kpsec.freeuk.com/555timer.htm
     

    Attached Files:

  9. May 22, 2012 #8

    Wow that was of great help as there is lot of such stuff present on the website that made me aware of many things that I didn't know about 555.
    I want to ask one thing here. . . On the website its written : "A low frequency astable (< 10Hz) can be used to flash an LED on and off, higher frequency flashes are too fast to be seen clearly. Driving a loudspeaker or piezo transducer with a low frequency of less than 20Hz will produce a series of 'clicks' (one for each low/high transition) and this can be used to make a simple metronome. "

    So does it mean that I must choose my C1=10uF ?(as my purpose is to blink the LED for 1 sec ON and 1 sec OFF)
     
  10. May 22, 2012 #9

    NascentOxygen

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    Staff: Mentor

    I would probably choose C1=2.2μF (or use a pair of 1μF caps in parallel).
    Note that electrolytic capacitors have wide manufacturing tolerances, perhaps as much as +100% and -50% so you should expect to have to adjust R or C to obtain precisely 0.5Hz if that's what you are aiming for.
     
  11. May 22, 2012 #10
    Okay :) Thankyou very much for your guidance:) I'll definitely come here with my results and let you all know how things turned out for me :)
     
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