Help with circuit project for newby

Discussion in 'The Projects Forum' started by LASERSC, Oct 11, 2010.

  1. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    I am trying to build a circuit to control (3)three 40 watt, 120v light bulbs. I want them to light in order A-B-C and then repeat continuously. Would prefer all bulbs to stay lit for about 15 seconds. A way to control the length of time each bulb would remain lit that is built in to the circuit would be nice as well. I am new at this and just don't know where to begin. Any and all help will be greatly appreciated.
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Would you be offended if we asked that you used a 12V transformer to reduce the mains voltage to a safe level then help you work out the circuit using 12V light bulbs or LEDs?
     
  3. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    offended? heck no! That would work great, probably a lot better that what I was going to do. Any help, diagrams, links, it would be great. And, thanks for your fast reply
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Excellent advice. The project will be orders of magnitude easier, cheaper and safer taking this approach. IMHO, it's actually MORE educational as well.

    LASERC, can you come up with some specifications? I mean, you started with 3x40w light bulbs. If instead you end up with 3 bright LEDs, is that OK? Do you want one of the lights on at all times (one goes on when another goes off)? Would you like to vary the rate that the lights switch? Anything like this that you feel MUST be included, let the folks here know and you'll find plenty of help.
     
  5. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    I already have light bulbs mounted where I need them, I can pick up 12V light bulbs at my local hardware store and fit right in the setup. I guess that fits my application better as it stands now. I am not against LEDs, just that light bulbs fit better in the enclosure I am using. I do want the bulbs to light one at a time. First A when A goes out then B lights and when B goes out C lights, then back to A to start over again continuously. Thank you for you help and I hope this explains it better.
     
  6. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    Oh, and yes it would be nice to be able to vary the rate. It isn't a must but would be nice. I would like for each bulb to remain lit for 15 or so seconds. I just don't want to make too complicated for anyone willing to help me.

    Thanks again
     
  7. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    Any help or links to help would be greatly appreciated. Thanks
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    LEDs, 555s, Flashers, and Light Chasers

    More for the intermediate user, some of the projects come very close to what you want. If you can light an LED, you can light anything.

    There are devices called SSR (solid state relays) that will work for both 12V circuits and AC circuits. They would use two different types of SSRs, but they are out there.
     
  9. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    Thank you so much, so I just install 12v light bulbs where they show the LCDs and that will work?
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    Do you mean LEDs? Not quite that simple, but close. You'll need a beefier transistor, but they are very cheap.

    This is an excerpt from an updated section I haven't released yet. Look at the bottom of the article.

    http://forum.allaboutcircuits.com/showpost.php?p=117646&postcount=11

    Radio Shack sells IRF510s at a markup, and it is only slightly over a dollar at that. Then you can replace the LEDs and the resistors (both are needed to equate to a light bulb) for the 12VDC light bulb.

    Hope this help, and if you have any questions keep them coming. We do try.
     
  11. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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  12. wayneh

    Expert

    Sep 9, 2010
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    A 12v bulb draws more current than an LED, so instead of driving the LEDs directly from the IC, you'll need to amplify the current with a transistor (or MOSFET, a special type of transistor). For a standard NPN transistor (or N-type FET) The signal will go to the "base" (or gate), and the main current will flow from the supply, through the current limiting resistor, into the "collector" (or drain), and out the "emitter" (source) to ground.

    You'll need a device rated for the needed current, and I'd go 2X or more to be sure it can handle it. That'll have almost no effect on price, so there's no reason to skimp. I'd go with a FET since your application requires full-on and full-off, for which a MOSFET is ideal.

    I've forgotten what sort of output the 4017 has, but you may need a resistor to pull the gate voltage up or down if the 4017 doesn't provide one or the other.
     
  13. LASERSC

    Thread Starter New Member

    Oct 11, 2010
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    Thank you wayneh, Maybe I do just need to stick with LEDs, I was reading where LEDs can produce as much light as a 12v 40w light bulb. Can a single LED do this and can it fit into the above 12v circuit without problems?
     
  14. wayneh

    Expert

    Sep 9, 2010
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    The short answer is NO. And even if you could find such a thing (which IS possible), it would still require more juice than the LED in the schematic, and therefore would need the current handling circuit I described. When you see "LED" in most circuits, it refers to the typical ~5mm device that draws 5-50mA and produces maybe 20,000 mcd peak intensity. Viewed on-axis, that can be very bright, blinding even, but it won't light up a room.

    But I think it's worth developing your circuit first with LEDs. You can buy them very cheaply on e-bay and maybe you'll be happy with them alone. If you get things working well and want more power, then make that change when you come to it.
     
  15. LASERSC

    Thread Starter New Member

    Oct 11, 2010
    9
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    OK, Thank you again, I am off to the local electronic store to purchase needed parts. thanks to all, and I will more than likely be back with more questions.
     
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