halloween blinking eyes

Discussion in 'The Projects Forum' started by iepaul, Aug 25, 2011.

  1. iepaul

    Thread Starter New Member

    Jan 26, 2011
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    I want to build a simple circuit to blink two leds that hopefully look like eyes for Halloween. I think the leds should be on for 2 to 3 seconds then be off for a short time (half a second maybe). I have built a led flasher circuit with a 555 but I have no idea how to achieve the timings above. The plan is to run it from a 9v battery and stick it in some bushes.
     
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
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    1µF, 2.7MΩ and 820kΩ will result in time high of 2.4s and time low of 0.6s. Use any online calculator or read the 555 data sheet.
     
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  3. Wendy

    Moderator

    Mar 24, 2008
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    I have about 50 of those suckers already. Capacitors are the hard part, match the resistors to the capacitors. When I built them in the course of several decades I deliberately did not use the same parts, I wanted wide variability in the flash rates.

    Use a capacitor to filter the basic power supply. They will still couple slightly (one changing will trigger another).

    Don't connect the battery backwards, the 555 will blow instantly. Because of this sockets are highly recommended.

    I went for a couple of seconds on and longer off, but like I said, I went for a large variation.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    I'd recommend using an RC tank on the base of a transistor to control the current to the LEDs, so that they fade in and out a bit instead of flash instantly full on or off. I haven't built such a thing, but I would expect it to look more "organic", and hopefully more creepy.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Like I've said, I've built a lot of them over time. For a while I would build 10 a year, sometimes less. If you want to see pictures I would be glad to post them, they have a lot of differences between builds.

    Quantity is a lot more spooky, especially with lots of differences. The idea is to have enough of them that when they are off (which should be more than on) you can't see them. Along with a spooky C64 Halloween sounds and some other special effects parents were heard to say "Go ahead, he has candy". The younger kids weren't convinced, it was great.

    Given the quantity of these suckers though, simpler is better. I like the cartoon effect, on then off. A diode in the right place (not in series with the power supply) could save you some 555 chips though.

    I have a decent fader circuit that uses a 555. But it also has two extra transistors. I don't think the fade in / fade out circuit would look as good.

    Want a schematic of the diode version?
     
  6. iepaul

    Thread Starter New Member

    Jan 26, 2011
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    I would be interested in looking at the schematic please.
     
  7. iepaul

    Thread Starter New Member

    Jan 26, 2011
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    "1µF, 2.7MΩ and 820kΩ will result in time high of 2.4s and time low of 0.6s. Use any online calculator or read the 555 data sheet"

    Can you tell me what schematic you used for these values please? The 555 calculators online all have slight variations.
     
  8. elec_mech

    Senior Member

    Nov 12, 2008
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  9. iepaul

    Thread Starter New Member

    Jan 26, 2011
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    Thanks that is a great link. Here is the circuit which I have. I am going to order up the parts today.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Here is a sketch of what I've done. Like I've said, there is a lot of variation in mine, depending on the generation. Basically with these suckers variation is good, you don't want them to all act exactly alike. Every time I built another batch I would look for the cheapest parts I could find. The capacitors are the expensive parts, the resistors are designed around them (and I used a grab bag for the resistors for the variation I was talking about).

    [​IMG]

    As you can tell, I've nicknamed them Bush Goblins. They are designed to be daisy chained, with one battery per bush. I used black and red tape next to the wires to mark the polarity.

    Here is the base diagram it was based on.

    [​IMG]

    Basically I have a blog with quite a few aids for designing this kind of stuff.

    I didn't use CR1 in mine, trust me, it will save you money. Even a momentary contact with backwards voltage will smoke several parts.
     
    Last edited: Aug 31, 2011
  11. wayneh

    Expert

    Sep 9, 2010
    12,103
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    What a great name! Might get you some unexpected hits if you google it, though. :eek::p
     
  12. iepaul

    Thread Starter New Member

    Jan 26, 2011
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    thanks very much for all the help. i will let you know how it goes.
     
  13. ElectroDFW

    New Member

    Sep 2, 2011
    15
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    This is why I miss the LM3909. Very simple LED flasher chip. Discontinued, unfortunately. Would blink an LED for a year off of one 'D' battery. I've tried transistor approches before, but will have to give these 555 ones a try. Thanks for the schems.

    --Electro--
    aka David M.
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    I've designed better already, check out my 555 articles. One of the designs is based off the LM3909, 5 different 555 flasers using 2X AAA batteries that flash an LED for a month or more (in some cases 3 months).

    In this case I have 4 different circuits, each more advanced than the last.

    The 555 Projects

    Part of the reason the LM3909 was discontinued is LEDs themselves have dramatically changed, Instead of dropping 1.5V for a old red LED the modern (and much brighter) red LEDs drop between 2.1VDC to 2.5VDC. It is a minor difference, but significant, and enough to render the LM3909 totally obsolete.

    In any case none of these circuits are suitable for bush goblins, you need several seconds (in mine up to 5 seconds or more) of LED on time. The current these LEDs are operating at is quite low, you don't need high intensity for bush goblins.

    Send me a PM or email (via my profile), I'd like to swap notes of local electronics outlets and other stuff. I live in Garland myself.
     
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