Small projects — up to a few dozen NeoPixels, maybe a couple hundred if you’re extremely selective about animation — can be powered with a lithium-polymer battery connected to SCORPIO’s JST socket, and recharged via the USB port. This is the most compact option for fully self-contained projects, such as wearables and cosplay.
Before proceeding, consider:
- As with all of these examples, you’ll need to do some wiring and soldering to distribute power to all of the NeoPixel chains.
- One should understand the safety and durability issues surrounding bare LiPoly cells. If this raises red flags, powering from USB (next page) might be preferable.
- To turn the circuit off, you’ll need a beefy DPDT switch (double pole, double throw).
- There are a number of other “gotchas” with this power arrangement, and one should have an intuitive understanding of issues discussed below. Consider using one of the other approaches if at all possible. This is only for the smallest, tightest situations.
Here’s a schematic diagram of how the parts connect. It’s laid out to make all the connections clear, though the actual physical wiring will likely take a different shape…and might have JST plugs on the strips, etc.:
This shows NeoPixel strips, but any NeoPixel-compatible part could be used (rings, dot strands, etc.), and in any combination. Most software (e.g. NeoPXL8 library) has an additional constraint that they’re all RGB or all RGBW; can’t mix the two types. Also, you don’t have to use all 8 outputs; fewer is fine if that’s all your project needs.
Remember that this arrangement is only suitable for smaller projects with few pixels lit; perhaps 1 Amp (1000 mA) overall. See the top page of this section regarding minimum and maximum per-LED current guidelines. This might suffice for a self-contained build of the Ooze Master 3000 project, where only a small fraction of LEDs are lit at any time. It does not “scale up.”
It’s unusual in that we’re using the ground connections at the end of the board as part of the power distribution; in larger, more power-hungry projects, power distribution to the LEDs is a separate thing, and those pads are only used for ground reference between board and power supply, not as current-carrying members themselves.
Positive voltage must be split from SCORPIO’s BAT pin to the 5V input on each of the NeoPixel chains — either wiring up a splitter or chaining one to next, or using part of a Perma-Proto board or a power distribution bus. The NeoPixels in this case are powered straight off the battery — nominally around 3.7V give or take — rather than the typical 5V, but this works fine.
You don’t have to run the ground wires this way. If it’s easier in your project to split or chain as done with the positive voltage, do that and use just one ground pin.
Notice the DPDT switch is used in a “staggered” configuration. In one position, only EN and GND are connected, powering off the board and disconnecting power to the NeoPixels (so they don’t drain the battery when “off”). In the other position, only BAT and 5V (to NeoPixel chains) are connected. Charge the battery with the switch in the “off” position.
Most small toggle switches are insufficient for this setup due to their limited DC current rating, sometimes just milliamps. Check the product info or datasheet, or use Digi-Key’s parametric parts search. DPDT switches rated for ≥1A are not inexpensive!
LiPoly batteries themselves have best practices for current draw that must be observed. Product info might mention something like a “C/10” or “C/3” discharge rate (e.g. can safely draw 1/10 or 1/3 of capacity per hour, respectively). The ones we sell have built-in protection against over-current.
When uploading new code to the board, the power switch must be in the “on” position. This presents a situation: the NeoPixels are being powered from ~3.7V, but logic signals from the board are shifted to USB’s 5V, exceeding the pixels’ supply voltage. All present-generation NeoPixels (SK9812 LEDs) have input protection and work fine this way…but other “compatible” pixels (WS2812, etc.), and old first-generation NeoPixels, may or may not. For maximum reliability in this situation, disconnect the battery when uploading new code, and conversely, set the switch to the “off” position when charging the battery.
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