# Hacking LED Effect Pucks



## drzeus (Jun 25, 2011)

Hi folks. I am hoping that some one on this forum might be able to answer a coupla questions about a prop I am currently working on.

For years, I have had this prop sitting on my porch (BELOW)-










Inside each of the "Pumpkins", I had one of these "pucks" (BELOW). Each one giving a different effect inside the JOL; a candle flicker, a strobe effect, and color changing.










Each one of these "pucks" operate on 3 "AAA" cells and must be turned on/off independently (Which is a royal pain to do each night during the season- not to mention- Expensive).
So I decided I was going to run all seven of these pucks off of 3 "D" cells (or perhaps a wallwart?) as below, so that they can all be turned of from one point (the manual toggle switch is not yet installed in image). Works good so far...










My first question is, does anyone have any clue as to a schematic to diagram a "light/dark switch" using a photoresistor for use in this configuration? The pucks would be powered on for (lets say) 8 hours starting at dusk, and turn off after that time.
I would hope to achieve 30 days worth of 8 hour cycles from of these 3 batteries (ideally). I could attach another 3 D cells to the mix if necessary or, as stated above, use a wallwart.
Based on mAh ratings of "AAA" vs "D" cells, and my knowledge of how long these pucks run on AAA's, I think the 30 day goal might be achievable. 
The walwart concept sounds best EXCEPT 1); this prop is kept on a covered front porch, but not immune from the rain And 2); concerned about irregularities in the output voltage of a ac\dc convertor. Is this something I should worry about?
Obviuously, it would be best for any circuit to operate off of 4.5 volt configuration as above.
How about just a timer circuit not using a photoresistor at all? Would that be a simpler build?

I do have mediocre soldering abilities but should be able to achieve a basic board.

I have even more questions once I can figure out the ones listed here!
Your help is much appreciated!
Thanx!


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## Jack Is Back (Jun 21, 2011)

I would say use a wart plugged into a photosensor AC plug. Unless you really have your heart set on making one yourself. As for the weather you could build some type of box to waterproof the wart.


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## The Pod (Sep 15, 2009)

First question, have you tested your setup to see if you can even get the full 240 hours (8 hrs by 30 days) with those three batteries alone?

I would suggest a 4.5VDC wallwart to be your better choice. Then you can just plug it into a simple wall timer and have it turn on at a specific hour and then off 8 hours later.


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## Otaku (Dec 3, 2004)

Agree with Jack is Back and The Pod. The only advantage to using an inline CdS sensor and batteries is portability. If thats not an issue, go with either a 24 hr timer or photosensor socket.


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## corey872 (Jan 10, 2010)

Just some 'back of the envelope' scratching:

I see 7 JOLs, so assuming 7 pucks. Each puck looks to have 3 LEDs and assuming standard 20mA current draw for each. So 7 pucks x 3 LEDs x 20 mA per LED = about 420mA current draw.

You said these to lighting 'effects' which probably means all the LEDs aren't on full power all the time. But, some circuitry has to drive that effect, so we will roughly assume the circuit draw balances everything out and you're pulling about 420mA continuously.

Quality D cell batteries are good for about 18,000 mA if you discharge them slowly, but likely to be around 12,000mA if you're discharging 400+mA rate. So, 12,000mA capacity / 420mA draw is about 28 hours - or about 4 of your 8 hour run-time days. (You're running the batteries in series, which boosts voltage while capacity stays the same, so no gain there) You would also need to consider the light/dark circuit is going to be drawing some power.

Another way to look at it, quality AAA batteries have a capacity of about 1,200 mA at those discharge rates. But you have 7 sets of those, so 7 sets x 1,200mA = 8,400mA total capacity in AAA cells. So I would expect the D cells to last only about (12,000/8,400) or about 1.4-1.5x what the AAA's last.

So at least in rough figures, there is not a huge gain in capacity switching from 7 sets of AAAs to one set of Ds - though your one switch point will certainly save some time.

If I had to do it quick and easy, I think I would yank the batteries in favor of a 4.5V wall wart with at least 500mA capacity. 1000mA or 1 amp would be even better. Replace your battery pack with the wart, and use the old " [2-prong male to lamp socket adapter] + [screw in dawn/dusk socket] + [lamp socket to 2-prong female adapter]" trick to make a quick dawn/dusk trigger.

The other consideration... 4.5V x 500mA is barely over 2 watts. You'd have to run that 500 hours to make 1 kWh, which is generally around 10 cents in electricity. So unless you just want the display off, it doesn't pay to be too elaborate in the timing switch...you're talking pennies per year in operation costs.


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## drzeus (Jun 25, 2011)

Thanks for all the input guys! Keep it coming- you got my wheels spinnin'!
The wallwart concept is something that I will certainly explore once my battery longevity test is complete- so far, the contraption has been running a solid 96 hours continuous (with 7 pucks). So the voltage fluctuation from a Walmart walllwart wont fry the prop?
I really like the "set it and forget idea" of the battery configuration but most likely, I will never get the 240 hours out of these 3 "D" cells to achieve 30 days at 8 hours each night (especially considering the additional drain of the light/dark sensor). I will report my final tally when this test is complete.


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## drzeus (Jun 25, 2011)

Thanks everyone.
The final tally was 120+ hours on the 3 "D" cells- enuff to give me 15 days at 8 hours each and, given my objective of 30 days, it falls short.
Given the short comings, I have two options; 1). Use a Walwart or 2). Double the number of "D" cells to give me my 30 days. 
The disadvantage to the later is that I would need to add a timer circuit to achieve that goal. Unfortunately, the circuit itself would require a portion of that longevity and reduce it even further. An alternate source (additional 9 volt) for powering the circuit could make it work.
Is it worth the additional cost?....Hmmmm...


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## corey872 (Jan 10, 2010)

Well, you ran a lot longer than I expected. The 'effects' must really cut down on the power draw. Personally, I'd still say just plug in a wall wart and let it run, or maybe do a simple dawn/dusk timer. You never have to buy/throw away/recycle batteries again and the display will always be at full brightness.


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## hpropman (Jul 27, 2008)

You have to make sure that you have a regulated wall wart to avoid an over voltage condition for the pucks and possibly damaging them. a 5 volt regulated wall wart would prob be easier to find and they will prob work fine at 5 volts or you can just drop a resistor in the line or a pair of diodes in series to drop the extra half a volt. let me know if you want to go that route and I can do some testing to give you a circuit and what you will need.


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