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Gemma, NeoPixels & 9v Battery
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Gemma, NeoPixels & 9v Battery

by joshuakane on Thu Apr 03, 2014 11:19 am

Hello,

I have put together a small project using a meter of the 30 LED NeoPixel Strips http://www.adafruit.com/products/1376. I know the strips require a 5v Power Supply, but I wanted to power the Gemma with a 9v Battery. What would be the best way to power the Gemma, and the LED strips and ensure they all work together while using the 9V battery.

-- Joshua

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Re: Gemma, NeoPixels & 9v Battery

by franklin97355 on Thu Apr 03, 2014 11:39 am

One thing to keep in mind is that 9v batteries are lousy at powering high draw items like neopixels. Look toward LiPo's.

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Re: Gemma, NeoPixels & 9v Battery

by pburgess on Thu Apr 03, 2014 12:25 pm

Or, if LiPo's (and associated charger) are too spendy...a 3xAA battery pack would work splendidly. The Gemma and NeoPixels are perfectly happy with the 4.5V output.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Thu Apr 03, 2014 1:02 pm

I think I am going to have to go the AA Route. The issue is it needs to fit in the hilt of a sword. I found some "Cylinder" style AA Holders. I think those would fit in the hilt well. The issue is they hold 4 batteries. I can modify it to just hold 3, and keep it at 4.5V. If I went up to 6v (4 batteries) and had the LED's off the VOut, would the voltage fry them?

Here is something similar to what I was looking at, I did not see an adafruit equivalent.

Image

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_mike on Thu Apr 03, 2014 2:20 pm

JoshuaKane wrote:If I went up to 6v (4 batteries) and had the LED's off the VOut, would the voltage fry them?

Yep.

You can drop the voltage to a safe level using a diode though: http://learn.adafruit.com/battery-power ... rips/diode
When you void a product warranty, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Mon Apr 07, 2014 9:19 am

I went to a local surplus place this weekend, and picked up the holder for the 4xAA batteries, I also picked up the diode ( 1N4001 diode 1A/50V). I am connecting to to the Gemma via the JST 2-pin connector. I can see that the Gemma powers up but the LED Strip does not. If I plug it into the USB connector on my PC it works fine. Is the diode I am using causing too much of a voltage drop?

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_mike on Mon Apr 07, 2014 12:34 pm

The diode drop should be between 0.6v and 0.8v. How do you have things connected?

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Mon Apr 07, 2014 7:52 pm

Hi Mike,

Here is an image of how I have it connected. Basically it is a 9V connector, with the Diode Soldered on the Positive wire. That is then Soldered to the JST-2 Connector, which is plugged into the Gemma. The Gemma Powers's up, and if I disconnect the 9V connector the lights flash for a second.


Thanks,
Joshua


Image

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_mike on Tue Apr 08, 2014 11:49 pm

Nothing out of the ordinary there..

What voltages do you see on the Vout pad when the Gemma gets power from the USB cable -vs- JST connector?

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Fri Apr 11, 2014 5:01 pm

Hi Mike.

The voltage out when using the battery pack goes from 4.99 to 5.01 V.

When using the USB it is at about 4.40 V.

Once or twice while trying to read the voltage i saw the lights light up with the battery pack but this was not steady.

This is using the 5V Gemma.

Thanks,

Joshua

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_mike on Sat Apr 12, 2014 12:15 am

The battery pack voltage looks a little low for a diode that isn't conducting much current.

Try measuring the current through the JST connector. That will involve cutting the VCC line to the battery pack so you can put the ammeter in line with the power, but it's the next logical thing to measure.

Also check your connections and wires for intermittent connections. The "pixels worked briefly" part sounds like a symptom of something loose.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Mon Apr 28, 2014 8:24 am

Here is something I noticed, and maybe it has to do with something particular to the NeoPixels.

I have the 4 x AA holder and the Diode conncected to the Gemma. When I read the Voltage from the VOut it is about 5.2. With this the LED's do not light. If I place a second Diode in line with the positive power line the voltage drops to about 4.5 and the LED's light as expected.

What are your thoughts on that, and would it matter if I used a longer say (2m) piece of the NeoPixel LED tape as opposed to my test strip of about 15?

-- Joshua

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Mon Apr 28, 2014 8:37 am

The Neopixels prefer that the signal voltage be close to the supply voltage. Since the Gemma digital pins operate at 3.3v, the Neopixels will work more reliably if the supply voltage not much higher than that. 3.7v LiPo cells work very well. When you get closer to 5v for thee supply, they do not work reliably with a 3.3v sgnal.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Mon Apr 28, 2014 10:18 am

So, if I use a 5v trinket, the 5.2v signal should work fine?

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Mon Apr 28, 2014 10:31 am

That should work.

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