I am reading the Adafruit Trinket tutorial here. It states that BAT+ is used for battery INPUT:

If you want to power the trinket from a battery or power adapter or solar panel or any other kind of power source, connect the + (positive) pin here!

So I'm slightly confused by the Adafruit LED skateboard tutorial, which uses this pin for power OUTPUT.

My questions:

  1. How can you use the power input pin for output?
  2. Why don't the LEDs draw way too much amperage through the Trinket board?

trinket diagram

  • \$\begingroup\$ Really really really nice diagram. Well researched, well written. Great question \$\endgroup\$ – Funkyguy Jul 30 '14 at 17:40
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    \$\begingroup\$ (The diagram is from Adafruit's tutorial.) \$\endgroup\$ – JYelton Jul 30 '14 at 17:54
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    \$\begingroup\$ @Adafruit Really really really nice diagram. \$\endgroup\$ – Funkyguy Jul 30 '14 at 19:34
  • \$\begingroup\$ @Funky lol - It does make me wonder if they are using Illustrator or some other graphics program to make these; they're quite useful for newcomers. \$\endgroup\$ – JYelton Jul 31 '14 at 18:15
  • \$\begingroup\$ @JYelton it looks like fritzing but the items in fritzing must be made in something like Illustrator. I wouldn't be surprised, adafruit is a very profitable company \$\endgroup\$ – Funkyguy Jul 31 '14 at 18:17

You are thinking of the power pin in a digital manner. The power pin is not set to be an input or an output. It is just the positive terminal of the power rail. If you want to power the trinket using a 5V power source, you'll put it in there since its the positive terminal. If you want to power another device that uses 5V and it just so happens that the 5V rail connects to the trinket as well, the device will still be powered.

The trinket isn't sourcing the power, the battery is, or in this case the power supply that the battery is connected to.

The LEDs aren't pulling their current from the trinket but rather the power supply. All the trinket is doing is sending the signal through the DIN pin.

  • \$\begingroup\$ Thanks for a clear explanation. Does this only work on the Trinket? How would you connect a Neopixel and a 2Amp power source to an Arduino UNO? (using the a 5V or VIN pins?) \$\endgroup\$ – Kokodoko Jul 30 '14 at 19:42
  • \$\begingroup\$ You should be fine, but before I say for sure, check to make sure that the power rails coming in from the USB connector don't go into the on-board regulator on the UNO. If they don't go in, you should (emphasis on should) be fine. At that point you should be able to connect them all at the 5V / BAT+ connections. \$\endgroup\$ – Funkyguy Jul 30 '14 at 19:48

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