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Gemma, NeoPixels & 9v Battery
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Mon Apr 28, 2014 9:07 pm

Hey Bill,

I hooked a 5v trinket up and wired up 2 one meter LED Strips. It is a total of 96 LEDs in two strips 48 LEDs on each. I have them sharing the power, ground and digital pin. When hooked up to USB the voltage out via the 5v is 4.5v. When I use my 4 x AA holder te voltage in is Close to 5v but the voltage out on the 5v output is close to 2.1v. The lights just light red or orange and don't funtion. I am guessing it is from the voltage being low. Any suggestions on how to resolve this. Also I have a few of your UBEC/buck converter if it will help.

Also just out of general principal I hooked up a 9v which may have been old, but it exhibited the same behavior.

Thanks,

Joshua.

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Mon Apr 28, 2014 9:26 pm

When I use my 4 x AA holder te voltage in is Close to 5v

The on-board voltage regulator needs some headroom to regulate properly. You should have at least 5.5v on the battery inputs.
Also just out of general principal I hooked up a 9v which may have been old, but it exhibited the same behavior.

9v should be plenty, but old ones do tend to droop badly under load. What do you measure on BATT+ when connected to the Trinket?

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Tue Apr 29, 2014 9:54 am

Hi,

Here is a really bad picture of the wiring diagram.for what I am doing. One observation in addition to the lights glowing orange is that the trinket gets very hot under the processor when I use the battery. When I use the USB connection it works well. I was hoping to be able to stay with batteries to keep the cost down, as I imagine using a 3.7v Lipo would add an additional $30 or so to the project.

Please let me know if there are some suggestions on how to improve this design.

-- Joshua

Image

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Tue Apr 29, 2014 10:24 am

96 pixels is way more than the 5v regulator on the Trinket can handle. I would not try to run more than 10 or so from the 5v pin. It is no surprise that it is getting hot when running from batteries. When running from USB, it is using the 5v regulator in your USB port. These can typically handle 500mA.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Tue Apr 29, 2014 10:39 am

Would a Micro be a better choice? I have used one of those in the past.

https://www.adafruit.com/products/1315

Also I have a UBEC/Buck I can use, but I don't know if that would help at all with the Trinkets.

https://www.adafruit.com/products/1385

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Tue Apr 29, 2014 10:54 am

Would a Micro be a better choice?

All the Arduino boards use linear regulators. You do not want to load these with that many pixels. The UBEC should work OK with a 5v Trinket.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Tue Apr 29, 2014 11:08 am

Great, Thanks Bill,

If I am following then, I can wire it up this way, correct?

Image

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Tue Apr 29, 2014 11:32 am

No. That is still trying to go through the Trinket regulator. Since the UBEC is itself a regulator, you can connect it to the 5v pin and bypass the internal regulator.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Tue Apr 29, 2014 11:49 am

Got it!

So something like this....

Image

Will I have to do anything to bypass the internal regulator? Is there something in the source code I should add to turn it off?

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Tue Apr 29, 2014 12:06 pm

I meant to connect the output of the UBEC to the 5v pin. As you have it drawn, you are powering the UBEC via the Trinket 5v regulator.

But actually, there is a better way to do it:
Connect your battery to GND and Bat+ as you have it drawn.
Then connect input of the the UBEC to GND and Bat+ also. This will let the Trinket run off it's own regulator and the UBEC will regulate power to the pixels.
battery
For the Pixels:
Connect the output side of the UBEC GND to the GND on the strip.
ALSO (to assure a good ground reference for your signal) connect a wire from the Trinket GND to the GND on the strip.
Then connect the 5v from the UBEC to the 5v on the strip.
And finally, connect your Pin 1 to DI on the strip

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Tue Apr 29, 2014 12:25 pm

Thank you so much!

I will set it up like this...

Image

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Tue Apr 29, 2014 12:46 pm

That looks better.

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Re: Gemma, NeoPixels & 9v Battery

by joshuakane on Tue Apr 29, 2014 7:07 pm

Here is the finished prototype. It will be used in a prop a friend is making. Thanks for the help getting it all set up.

http://www.youtube.com/watch?v=8SqfMz6l4Cs

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Re: Gemma, NeoPixels & 9v Battery

by adafruit_support_bill on Tue Apr 29, 2014 8:08 pm

Very nice!

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