NeoPixel Stick(s) detailed Specifications

[NovaDom]

Good evening everybody;

I'm sorry to bother you with something that will be either really easy to answer or just plain stupid to ask.

I've only begun fiddling with electronics, and my knowledge is very limited.

Quick explanation of what I'm trying to do, to give a picture of the project.


I have a arduino UNO that I want to use to control 2 Neopixel Stick.
(Other components will be added later on, but I want to make sure I understand this first)

The power source for the arduino will be a 7.4V Li-on battery.

I want to use a NPN transistor (connected to a PWM pin of the arduino) to 'control' the lighting from the Neopixel Sticks.

Both NeoPixel Stick will be connected in series.

I'm trying to figure out the transistor to use, and for that I need some informations about the NeoPixel Stick that I didn't find.


Well, actually, to start I have two conflicting specifications:

on the NeoPixel Stick webpage, it says that
Each one has ~18mA constant current drive

While in the NeoPixel uberGuide, it says that
Each individual NeoPixel requires 60 milliamps max at full brightness

If one NeoPixel Stick is 8 individual NeoPixel, how could that total to 18mA ?

I'm trying to calculate the total current drawn from my two NeoPixel Stick!


Also, is it possible to know the voltage drop accross the two Sticks?


Next, in the NeoPixel Stick webpage, it is stated that:
Power the whole thing with 5VDC (4-7V works), does that mean I should use 5V as forward voltage in my calculation?


Finally, in the 'Best Practices' webpage it is stated that I should use a capacitor (1000 µF, 6.3V or higher) and a 300 to 500 Ohm resistor if the setup is powered by a plug-in power supply.
Since this is a raally small project, powered by a relatively low power battery, do I risk damaging the NeoPixel Sticks if I don't use those parts?

thank you very much for your help in advance, and have a great day

[adafruit_support_bill]

I want to use a NPN transistor (connected to a PWM pin of the arduino) to 'control' the lighting from the Neopixel Sticks.

You cannot control them that way. As the product description says

Each LED is addressable as the driver chip is inside the LED. Each one has ~18mA constant current drive.

You control the individual leds on the stick with a one-wire serial protocol using a ttl logic pin. (Our neopixel library takes care of the low-level details of that).

Since each neopixel has 3 leds (red green and blue) with a maximum of 18mA - plus some overhead for the chip itself, 60mA per neopixel is the maximum current draw.

Since each led has its own constant current control, you do not need to worry about forward voltage or current limiting resistor calculations. Just supply it with a steady 4-7v.

For a battery powered project, the capacitor is probably not necessary. A resistor on the signal pin is still recommended. And do heed the cautions regarding making connections and care in handling them to avoid damage from static discharges.

[NovaDom]

Since each neopixel has 3 leds (red green and blue) with a maximum of 18mA - plus some overhead for the chip itself, 60mA per neopixel is the maximum current draw.

Since each led has its own constant current control, you do not need to worry about forward voltage or current limiting resistor calculations. Just supply it with a steady 4-7v.

I'm not sure I understand correctly..
Will the Neopixel stick be powered FROM from the arduino uno? (I thought that the output pins of the arduino could only provide 40mA maximum?)
or rather

(I have a feeling this is correct) I connect both Neopixel in series, I then wire my power source 4-7v directly to the first NeoPixel Stick, and then I wire a PWM pin from the arduino uno to the input pin DIN of the first NeoPixel Stick, and that's it? I'd be able to control each led independently on the sticks this way, thru coding?

[adafruit_support_bill]

The neopixels have 3 pins on the input end: GND, V+ and signal input.
and 3 pins on the output end. GND, V+ and signal output

The stick is powered by GND and V+.
The pixels are controlled by the signal input.

I connect both Neopixel in series,

Correct

I then wire my power source 4-7v directly to the first NeoPixel Stick

Also correct

and then I wire a PWM pin from the arduino uno to the input pin DIN of the first NeoPixel Stick

No. It is not controlled by PWM. It is controlled by a one-wire serial protocol as implemented in our neopixel library. You can use any Arduino pin for this.

Please read through our Neopixel Überguide. It explains the wiring and the coding for these devices in detail. Pay particular attention to the "Best Practices" page. It is easy to damage these devices if not wired correctly.

[NovaDom]

Thank you very much for your concise explanation! I think I got it now!

I think I also understand my earlier confusion...
At the beginning of my project, I was thinking of using regular 5mm RGB common cathode LEDs to get the color I wanted (hense my using of the PWM pins)

I changed my minds after seeing a video showing what the Neopixel Sticks could do
(and I was trying to use the exact same wiring scheme as with the standalone RGB leds.. which I know now is wrong)

I also realized now how much simpler everything will be to wire (and to control) with the Neopixel Sticks!