Delay multiple circuits

Discussion in 'The Projects Forum' started by Socratia, Aug 27, 2013.

  1. Socratia

    Thread Starter New Member

    Aug 27, 2013
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    Hello, I'm working on a costume project with a lot of lights. I've got a bunch of completed circuits all running off of a single 12v 2.9Ah battery. I want to introduce something to a few of the circuits to delay their lights coming on after power is supplied to everything. I would prefer they come on in sequence as well. I'm not sure what item to use but I would prefer it be small. I only need a 2-3 second delay at most. Any ideas?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    One solution would be 555 timer IC used as a clock, followed by a 4017 counter and finally a MOSFET switch for each power circuit. Each tick of the clock would advance the counter and turn on the next circuit.

    Oh wait, that would turn off each circuit is sequence as well. So much for thinking out loud. But it's a start. We need something other than the 4017. You need something like a bar graph, where the number of lights "on" increases one at a time with each clock tick. The name of such a thing is not coming to me!
     
  3. #12

    Expert

    Nov 30, 2010
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    That's an LM 3914 or 3915. You want the linear one set to "bar" mode.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    That would work. Instead of the clock I was talking about, you would just use a resistor feeding a capacitor to give a voltage ramp to the LM3914. Use a large ohms resistor to drain the capacitor when the system is off.
     
  5. Socratia

    Thread Starter New Member

    Aug 27, 2013
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    Can I find these things at Radio Shack (or any store similar)? I'm in a bit of a time crunch now with needing to have it this weekend.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    I know I cannot obtain it locally. You could use Mouser, Newark or DigiKey and have it by the end of the week.

    Or you could take a different approach. How many circuits do you have? How much current does each require?

    Here's a brute force approach for which you'll need one complete control for each circuit. For each, you make an RC timer. Use the voltage on the capacitor to drive the base of a darlington transistor. All of these components are at the Shack, eg. TIP120 darlington.

    You'll need do some calculation of delay time, or just get several capacitors and resistors and experiment. Note that the transistor will conduct current from its base to ground and thereby discharge the capacitor, so you don't need to worry about that.

    Another approach, if you have 4 or less circuits, would be to use the LM339 quad comparator. Each comparator could watch the voltage on an RC timer (with much smaller capacitors and larger resistors than the brute force scenario above), compare it to a reference, and then switch a MOSFET such as IRF510 to turn on each circuit. I'm not sure which would be easier, 4 RC timers and one reference or 4 references and a single RC timer. Probably the latter.
     
  7. Socratia

    Thread Starter New Member

    Aug 27, 2013
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    I've got 4 circuits that need a small delay. The first has 2 devices that need 6V a piece. The second has 4 devices needing 3V per. The next 2 circuits both have 4 LEDs that draw 3.3V per.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Are these all functioning already with 12V, or do you need to set them up also? [edit] I see in post #1 that you said they are all working.

    You haven't said how much amperage each needs. That only effects what power transistor you need.

    If you've never used a comparator, I think I'd just go brute force as above. I use comparators often but I'd lean towards the brute force anyway. You need 4 transistors for any solution, and just 4 resistors and 4 capacitors for adding brief delays. Tough to beat the simplicity of that.

    Your timing resistors need to be less than 8kΩ. Maybe plan on 1k, 1.2K 1.5k, 1.8kΩ. Use and RC calculator such as this or this to get the timing you want.
     
    Last edited: Aug 27, 2013
  9. wayneh

    Expert

    Sep 9, 2010
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    Hmmm... Electrolytic capacitors are not cheap at the Shack, since you need at least about 1000µF.

    You can use larger resistors and smaller caps. Take a look at 3.3k, 3.9k, 4.7k, and 5.6kΩ with a 470µF capacitor.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Where in the country are you located? Some cities have some old-school electronics stores. If you live on the west coast, Fries Electronics will have the 3915 mentioned above.
     
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