Low-Cost Illuminated Display

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robodude666
 
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Joined: Sun Mar 28, 2010 12:12 am

Low-Cost Illuminated Display

Post by robodude666 »

Hey All,

I'll be getting married in two months, and as part of the BANNED we want to have a centerpiece for each of the 20 tables.

The center piece will be a cherry base, with a rose inside, covered by a 6"-diameter, 9.5"-tall bell jar (If you've seen Beauty and the Beast, we're re-creating The Enchanted Rose in Beast's West Wing).

At the base will be a collection of small diamond-looking gems (to help refract light), and under the gems we want to have a small collection of lights to illuminate the rose. Overall, it's not very difficult to make. Except when you're trying to make it low-cost and low-power.

Currently, I have envisioned a little ATTiny, li-ion battery, and a collection of WS2812S RGB LEDs. In the proof-of-concept I made, I ended up curling ~16 inches of Digital RGB LED Weatherproof Strip under the gems and it looked beautiful. The display needs to have RGB LEDs to recreate the shade of pink required, and be able to go into a "party" rave mode. However, with about 20 LEDs on that strand, each display cost around ~$10-15 for the parts, not to mention the battery. Those LEDs consume a lot of power, and 20 of them at full brightness would be 1.2A. We'll be needing the display to be on for at least 4-5 hours. A battery that size will cost at least $15-20 each, and be fairly large.

What would be ways of reducing power consumption and reducing overall cost?
  • Would it be cheaper to find generic RGB LEDs and a driver IC or larger 40-pin MCU and drive the LEDs manually?
  • Would I be able to get away with fewer LEDs than 20 per display? The display will be on through most of the day, and then a couple hours into the night.
  • Would there be an optimal spacing or layout of LEDs to fully cover the 6" diameter base?
  • What about a diffusor? Would that help in reducing the number of LEDs required by evening out the light over the area?
  • Is there a low-power version of the WS2812S LEDs available somewhere? Even with 3.3V input they still draw ~60mW.
Overall, I'm trying to get down to <$10 per table or as close to it as possible.

Any other suggestions?

Thanks!

-robodude666

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adafruit_support_mike
 
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Re: Low-Cost Illuminated Display

Post by adafruit_support_mike »

It sounds like you're caught between the laws of physics and economics, especially when it comes to the batteries. That means you need to set yourself a budget and work to it.

In this case, you need a battery-powered system that can run for several hours. At consumer prices, that means using D cells. The usable energy in a battery depends on how much current you draw at any given time, but at 500mA you should be able to get between 7500 and 10,000mAh out of them, or 15-20 hours of use. Be warned: going up to 750mA will probably drop the lifespan to about 4 hours, so use 500mA as your target.

On that power budget, you can run about 8 NeoPixels flat-out, or about 16 at a 50% duty cycle. Color mixing will play into that because you can't get pink without shutting down the green LED while the red and blue ones are still glowing, but you'll need to trim your ON/OFF times so the average duty cycle is 50% or less. The fewer pixels you use, the more power you'll be able to budget to each one.

Combining the power budget and financial budget should give you a fairly good idea of how many pixels you want to use per table, so start experimenting in that range to see what you can build that you like. Expect to drain some batteries on full-lifespan testing just to make sure the setup will work as it should when it should.

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robodude666
 
Posts: 120
Joined: Sun Mar 28, 2010 12:12 am

Re: Low-Cost Illuminated Display

Post by robodude666 »

Wouldn't I need more than one to get the 3v+ required, or one with a boost converter? Can you drive the NeoPixel LEDs with only ~1.2V from a single D-cell?

It would be cheaper to get 2 D batteries @ 2.5$ each than to spend $5-10 on a DC-DC converter, but that adds a lot of size. I originally considered lithium-ion batteries because I wanted everything to fit into the base, which was going to be 5/8" thick.

Thanks,
-robodude666

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