Wireless LED torch

Community Projects
1

Hi all -

I am working on a virtual reality installation for the Museum of Fine Arts in Boston which involves real-world lights.

I need some advice on building a physical “torch” involving some RGB LEDs being controlled by a laptop via Xbee. Here is some relevant info:

  • Wireless (we have an Xbee set up, and are planning on using an Arduino Pro-Mini, or similar housed within the torch to drive the LEDs), so everything has to be compact and lightweight.

  • The room will be darkened, but I’d like the LEDs to be reasonably bright and colorful (with whatever power supply I end up with).

  • The power supply needs to be light and mobile, so I am thinking LiPo, if I can get enough juice out of it.

  • The event is about 5 hours long. I could change out the battery pack during the event if necessary, but it would be a big benefit not to have to do that.

  • The LEDs will generally be running some flickering animations with some color shifts, so mostly not at full-power white, except for a moment here and there.

  • The LEDs will be housed in a frosted glass case, and so I don’t need a lot of LEDs… Just enough to be seen from all around. I am assuming a strip, like the NeoPixels is ideal.

  • If I get a strip, probably a 30-LED half-meter would be fine.

  • Looks like 30 might be power-able right off the arduino power pin – or would I want to power the arduino and the strip separately, but from the same battery so the strip is getting full current out of the battery (with a small current-limiting resistor thrown in for safety)?

My questions:

  • Any recommendations on the combination of LED / battery / arduino for a hand-held, lightweight application like I describe? From my research so far, I think I could do a 30-pixel Neo strip, with a LiPo battery, and a Pro-Mini 5v. Will I be able to power the strip with that set up? Any chance I will get 5 hours out of the battery?

  • If anyone has a different suggestion than NeoPixels, I’m up for it. I do have experience working with circuit design, and arduino - but it is a goal to keep everything as easy as possible (most of the work is on the virtual reality side), so I’d rather go with a solution that is straight forward, and easy to get rolling - even if it costs a little bit more.

Please let me know if my assumptions so far are sound, or if you have any other suggestions - thank you!

Dare M

2

To estimate battery lifetime in a given application, first measure the average current draw of the circuit in mA. Then decide how many hours you want the circuit to run and multiply the two together to get mAh (milliampere-hours), which is a measure of required battery capacity.

Buy a battery with at least that number of mAh (and to be safe, twice that). The stated capacity is only a rough approximation, because as the current draw increases, battery capacity decreases.

Note: you cannot power more than one LED from an Arduino pin.