neopixel ring + 6v lamp battery + pro trinket/gemma/trinket/

[kgreene]

I'm trying to do a variation of the neopixel flashlight for an elementary school project, each student in the class will make one or some part of it:

http://makezine.com/projects/million-co ... lashlight/

I'm trying to reduce the cost so I was thinking of trying to use the 6v lantern battery for power (it comes with the lantern). This will change the design somewhat because I can't depend on using a 5v power supply directly for the neopixels.

I've looked at the pro trinket (3 or 5v), gemma, trinket, arduino pro mini (3 or 5v), and the beetle.

At first I thought I could use any with a built in voltage regulator and use the output to power the leds, but the output seems to be capped around 150mA and the neopixel guide says worst case for each is 60mA. So that would only get me 2-3 leds. It does say you could probably plan on less but that really depends on the program used to control them.

So, the problem seems to be supplying the controller and the pixels with the appropriate respective power.

I've seen some say that you can use a 6v input and just use a diode or two to drop the voltage for the neopixels. I was originally looking at a 7805 voltage regulator but it sounds like that will be problematic because 6v isn't enough to get the correct output.

It sounds like the options come down to:

- 6v + diodes to the neopixels and controller (or straight 6v to a board w/a regulator)

- 6v + 7805 instead of diode as above

- 6v straight to a regulated controller, use the regulated output to control the neopixels but reduce the number of leds, maybe 7 pixel ring or smaller
- as above, but just make sure the 12 pixel ring stays at a lower brightness (how does the controller handle overdraw? will it just temporarily shut off or burn something out? - kids may be programming some of it so there's room for error...)

- Scrap the 6v idea, use some AA battery pack of some type. I'd appreciate comments on the 3v vs 5v options in this case. I'd prefer to NOT use lithium batteries in a school setting.

A couple other things to keep in mind, I'd like the option of a usb interface if possible to make it easier for the kids to program. (I'm unsure if we'll get that far, I'll preprogram them first but I wanted that option if possible.) It would be even nicer to not have to install custom drivers. (mac os x laptops)

Obviously cost is a major factor here, but I'm willing to spend a couple extra dollars to simplify a design considerably.

Any help appreciated. I posted this in the education forum, maybe the glowy things one would be better? Don't want to cross post really unless that's OK here...

[adafruit_support_bill]

The specs for that project are a little sketchy, but it looks like they are powering it from a 9v battery using the on-board voltage regulator on the mini. Seems to me there would be a lot of stress on that voltage regulator.

You could probably drive the Arduino from the 6v cell instead. The regulator would rather have more like 7v for stable operation. But it would probably work OK at 6v and it would have less heat to dissipate than with a 9v source.

The other option is the diode drop. A silicon diode would drop the 6v down to about 5.3. You could power things directly via the 5v pin.

[kgreene]

Thanks.

It's sort of buried several pages in but they recommend 4x AA NiMh to give ~4.8-5v (it says do NOT use alkalines which would give ~6v).

Do you really think the 150mA output from the trinket/gemma/etc would work with the 12 or 7 neopixel ring?

Or does the 12 (or other size, 7 or 16) work off the 6v directly? Looking at the pages again, the neopixel ring page says 4-7v but the 12 ring page says 5v. The neopixel guide seems to say >5v directly into the ring would be bad, but 150mA 5v wouldn't give me a lot of options led number wise.

If the 12 ring neopixels can REALLY handle up to 7v, it seems like I could get away with a 6v lantern battery directly to both the neopixels and the arduino. If I could get confirmation on this that would mostly solve my problems except for deciding on the the controller.

[Franklin97355]

A LDO regulator might get you closer with a fully charged battery. http://www.jameco.com/1/1/34859-l4940v5 ... itive.html

[adafruit_support_bill]

Neopixels by themselves can't handle more than about 5.5v. Some of our smaller Neopixel boards have current limiting added. I don't see any on the schematics for the 12 pixel ring. Assuming that you have the 6v batteries to start with, the diode drop approach is probably your simplest and lowest-cost alternative.

Given that this is being used as a lantern, I'd expect that the pixels will be driven close to max output. So I would not recommend trying to drive them through the 5v regulator on the Trinket.

[kgreene]

Could you check the 7 LED neopixels? At least the different white 7 pixel ones say 4-7v, the RGB only one doesn't. It'd be good to know if the plain RGB also supported 4-7v since it's cheaper. :)

If the 7 pixel boards work, that would be even simpler if the controller and the pixel board could both connect to the 6v.

[adafruit2]

so here's the thing - while any/all neopixels are 5V devices, you could (at least historically) give them 4-7V and they'd work fine. it isnt suggested, and a lot of people dont realize that, say, batteries are 'nominal 1.5V' so they end up way overvolting. stick to <5.5V if you can! :)