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SpokePOV + NeoPixel strip = Just take my money
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SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sat Dec 05, 2015 7:25 am

So I just ran across your SpokePOV combining my love of biking, electronics, lights and programming. I'm wondering if I can replace the regular LED's with a cut piece of 144 Neo-Pixel strip so 30 pixels per side from that strip? Maybe the 60 NeoPixel strip would be dense enough to make nice pictures as well, i'm not sure.

I can haz please? :)

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Re: SpokePOV + NeoPixel strip = Just take my money

by adafruit_support_bill on Sat Dec 05, 2015 7:32 am

The SpokePOV is a older design that pre-dates digital LED strips. The refresh rate on the Neopixels is a bit slow for POV applications, but the newer DotStars work pretty well for that.

Here is a tutorial for a bike wheel POV using DotStars and a Pro Trinket:
https://learn.adafruit.com/bike-wheel-pov-display

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Re: SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sat Dec 05, 2015 7:27 pm

Very cool. By "Work pretty well with that", you mean not as good as the regular LED's?

Becky says in her tutuorial that 1/2 a meter is good for 1 bike wheel, about 72 pixels, Any idea what kind of time she got out of her 3 AA batteries? That's always my concern it seems because I hate the idea of having to swap batteries every 20 mins.

Anyway, i'm thinking of doing 2 sets per wheel to increase the persistent effect, would you run the trinket off one power supply, then use a separate power supply for the 144 pixels?

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Re: SpokePOV + NeoPixel strip = Just take my money

by adafruit_support_bill on Sat Dec 05, 2015 8:00 pm

you mean not as good as the regular LED's?

It is always possible to update regular LEDs faster than with the serial protocols used by the strips. But the DotStars are plenty fast enough for POV.

Any idea what kind of time she got out of her 3 AA batteries?

That really depends on the pattern you are running. For most patterns, you should get better than an hour from a set of good AA cells.

Code: Select all | TOGGLE FULL SIZE
would you run the trinket off one power supply, then use a separate power supply for the 144 pixels?

You can run them both off the same supply. The Trinket will draw less current than a single pixel.

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Re: SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sat Dec 05, 2015 9:34 pm

Great, it sounds like I know what i'm getting for Christmas then. You have been really helpful, so I hate to ask another question, but:

You told me that hooking batteries in series to increase amperage is bad because of something to do with back charging, so I was wondering if there was a circuit I could build, say with a diode, that would allow 2 sets of 4 NiMH AA batteries in series safely. Im not knowledgeable enough to ask google a proper question with the right vernacular to find an answer.

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Re: SpokePOV + NeoPixel strip = Just take my money

by adafruit_support_bill on Sun Dec 06, 2015 7:52 am

You told me that hooking batteries in series to increase amperage is bad because of something to do with back charging,

I don't think so. Back-charging can happen when you wire them in parallel. Not serial. NiMH cells can be used in series with no problems.

Lithium cells should be factory matched and balanced for use in serial or parallel configurations.

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Re: SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sun Dec 06, 2015 10:54 am

Er ya, parallel that's what I meant. Thanks.

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Re: SpokePOV + NeoPixel strip = Just take my money

by adafruit_support_bill on Sun Dec 06, 2015 11:29 am

You can use a diode in series with each cell to prevent reverse flow. Just make sure that the diode is rated for the current you expect to be drawing. Also note that there will be a voltage drop across the diode. Schottky diodes have lower voltage drops than silicon diodes, so they would be a better choice.

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Re: SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sun Dec 06, 2015 11:39 am

Thanks, but I was trying to do something impossible. I wanted to increase my amp hours by putting two sets of 4 batteries in parallel. So ~5V at twice the amp power. ( With rechargeable NiMH batteries )

With the voltage drop though I don't see how you could wire a circuit to prevent backflow in parallel and do what I want.

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Re: SpokePOV + NeoPixel strip = Just take my money

by adafruit_support_bill on Sun Dec 06, 2015 12:14 pm

With 2 sets of 4 NiMH cells and a Schottky diode in series with each set, you would get about 4.5v after the diode drop. Using 2 sets of 5 NiMH and silicon diodes, you would get about 5.3v.

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Re: SpokePOV + NeoPixel strip = Just take my money

by Disciple on Sun Dec 06, 2015 8:57 pm

adafruit_support_bill wrote:With 2 sets of 4 NiMH cells and a Schottky diode in series with each set, you would get about 4.5v after the diode drop. Using 2 sets of 5 NiMH and silicon diodes, you would get about 5.3v.
That's good to know for battery projects in general. But I just can't help picturing a heavy mass of batteries whirling at the limits of breakaway on a shuddering bicycle wheel. Would the diode solution make lithium-based rechargeables safe in parallel? I would hope they could be kept above 3.3V.

Hallelujah!
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Re: SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sun Dec 06, 2015 8:58 pm

adafruit_support_bill wrote:With 2 sets of 4 NiMH cells and a Schottky diode in series with each set, you would get about 4.5v after the diode drop. Using 2 sets of 5 NiMH and silicon diodes, you would get about 5.3v.


Ok I lost you. Are you saying that I can get twice my amperage by doing that and not have to worry about backflow?

Like this image except instead of a solar panel, it would be a second set of batteries?
Schematic-solar-panel-circuit-with-battery-backup.gif
solar panel / battery backup
Schematic-solar-panel-circuit-with-battery-backup.gif (17.56 KiB) Viewed 1325 times

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Re: SpokePOV + NeoPixel strip = Just take my money

by SirChuck on Sun Dec 06, 2015 9:05 pm

Hi Disciple, I should be able to handle 8 - 10 batteries on my bikes wheels, just a matter of balancing them around the wheel hub. The extra weight isn't a problem because i'm using it for exercise anyway, well that and to impress the pretty nerdy ladies with sparkly lights.

Hopefully they won't view this forum so they think i'm the smart one and not Bill. :P

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Re: SpokePOV + NeoPixel strip = Just take my money

by adafruit_support_bill on Mon Dec 07, 2015 7:24 am

Ok I lost you. Are you saying that I can get twice my amperage by doing that and not have to worry about backflow?

Yes. As drawn, you will get double the capacity and protection against backflow.
Would the diode solution make lithium-based rechargeables safe in parallel?

That is still not recommended for lithium cells. While it protects against backflow, it does not guarantee balance between the cells. And unbalanced lithium cells can be dangerous. If one cell has a lower internal resistance than the other, it will carry a greater proportion of the load. If it overheats it would become a fire/explosion hazard.

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Please be positive and constructive with your questions and comments.