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Neopixel rgbw and capacitor
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Neopixel rgbw and capacitor

by ltodd2 on Tue Dec 24, 2019 7:10 am

Hi all
I started a question about on another thread https://forums.adafruit.com/viewtopic.php?f=57&t=159947&p=788247#p788247 about using the pixels with a feather. Ive change from that to looking at using a trinket M0 mainly for its small size. Im going to be using either 3 or 5 individual pixels. for such a small number is the 0.1uf decoupling cap needed on each pixel and will it also need a 1000uf cap and resistor at the beginning? It will be powered but a 3.7v lipo using the lipo backpack board to allow charging. Im wanting to keep this as small and light as possible.

As for power needed im not sure on battery size. looking at the 150 upto 400mah ones. I know the pixels take 20ma each max. if working on 5 pixels i will have 2 on full brightness red, 2 full brightness green with the white giving a double flash on those every second and the colour is off while the white is on. The 5th pixel will just be a double flash every second in red. can i just work on it will be approx 80ma give or take a bit for the flashing red? Still trying to find the power draw for the trinket M0. Im wanting this to ideally run for 1.5 to 2 hours. Im guessing the adafruit lipos will cut off when the voltage is too low as not to kill them?

Thanks all and have a merry christmas

Lee

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Re: Neopixel rgbw and capacitor

by adafruit_support_bill on Tue Dec 24, 2019 8:27 am

With a small number of pixels powered by LiPo, you can omit the 1000uF cap on the power source. But the .1uF decoupling caps per pixel are generally necessary for stable operation.

i will have 2 on full brightness red, 2 full brightness green

Full brightness red or green will require about 20mA per pixel.
with the white giving a double flash on those every second and the colour is off while the white is on.

If by white you mean just the white channel, that is 20mA per pixel also. Full white would be with all channels on and would require closer to 80mA.

Depending on how long your flashes are on the 5th pixel, I'd estimate about 85-90mA. to be safe. You can divide the mAh rating of the battery by the mA of your average current draw to estimate your run-time. 250mAh / 90mA = 2.78h.

https://learn.adafruit.com/sipping-powe ... s/overview
https://learn.adafruit.com/energy-budgets

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Re: Neopixel rgbw and capacitor

by ltodd2 on Tue Dec 24, 2019 10:03 am

Hi

Thanks for for reply. I will add the decoupling caps then. Would the resistor on the data line be needed in this setup?
Looks like 250mha would be plenty for the leds, just got to go find the power of the controller now

Thanks

Lee

ltodd2
 
Posts: 23
Joined: Mon Apr 06, 2015 12:14 pm

Re: Neopixel rgbw and capacitor

by adafruit_support_bill on Tue Dec 24, 2019 3:06 pm

The termination resistor for the data line is only needed for longer runs. If the data line is less than a foot or so it is not necessary.

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