Beginner: how to hook up battery pack?

TL;DR: The Trinket Pro 5V user guide says that it’s easy to hook up battery packs by connecting the positive to the BAT+ pin, but what do I do with the negative coming from the battery pack?

My apologies in advance, for any of you who know anything about electronics (which is all of you!), this is going to be probably the most boneheaded question you’ve ever seen.

But I’ve gone my whole life without knowing anything at all, but I grabbed a couple of Arduino-compatible devices (Adafruit Trinket Pro 5V and Mini Trinket 3.3V) to see what the deal is and why people are so crazy about them.

I managed to follow these instructions ( to get three LEDs blinking and my first simple project worked right off the bat! I’m more impressed that I didn’t manage to destroy anything (also my first time soldering anything).

But now I want to figure out how to power this thing with a battery pack instead of via USB. Basically, here’s my project idea: my 3 year old wants a robot costume at comic con, so I’ve figured out how to get three flashing LEDs on a breadboard - but only powered via USB - so this robot will have some flashing lights, and I’ve figured out separately how to hook up a 9V battery pack to a 12V CPU fan (to keep the helmet cool). Not bad for a newbie!

My only problem at this point is I don’t know how to hook up a battery pack to the Trinket Pro to have it work on the go. As far as I understand, there should be no problem powering the 5V Pro with a 9V battery. (I can get a new battery pack if there’s a better option)

The Trinket Pro 5V user guide says that it’s easy to hook up battery packs by connecting the positive to the BAT+ pin, but what do I do with the negative coming from the battery pack?

I’ve attached a photo of my breadboard with Trinket Pro attached.

It goes to the terminal marked GND

It goes to the terminal marked GND


Moderator edit: unnecessary sarcastic comments removed

raschemmel, it's easy for a guy with 35 years of experience like you. I've got about two days of experience and almost all of it was spent googling. Unfortunately, I don't have the knowledge yet to even know what exactly to search for. I kept finding things that were intended for extremely (to me, anyway) advanced projects and I couldn't find the basics. I did read through a number of tutorials, but none of them tackled the particular subject of connecting battery packs. I've never taken a class, never done any projects, and am trying to learn bit by bit.

I mentioned that I was a complete beginner, so if this is the way that you treat people who come for help, I don't think that this is the place for me. This community is obviously targeted towards hobbyists, not people struggling with the basics. Thanks for the hospitality.

BTW, before posting this, I did try connecting the negative to GND, as that's pretty much what hours of googling will suggest is correct. But the LEDs didn't light up like they did when plugged in via USB. The LEDs had a very faint glow. That's why I figured that GND wasn't the right way to go and I came here. Maybe there wasn't a good connection, I don't know. The battery pack does work when I connect it to the 12V fan, and the battery is new. So it didn't work when I tried it, I thought I'd ask people who know what they're doing. I don't want to do anything that'll fry my Trinket.

Anyway, I'll show myself out now. Have a good time with your hobby. I'll find somewhere else to ask my questions.

[quote author=Runaway Pancake date=1465137399 link=msg=2786825] It goes to the terminal marked GND [/quote]

Thanks for the reply! I mentioned in my other reply that I had tried this, but the LEDs just glowed faintly, so I figured I wasn't doing it right.

I assume you have connected 12v to Bat+ and GND. You also might be using a resistor in series to LED, what's the resistor value?

If you are using a high value resistor then the LED will not be bright. Try to use a resistor of 390 or 420 ohm.

If there was an issue with GND then LED wouldnt even light up.

Dont take things too seriously here, some times you might feel harsh but Raschemmel managed to post a diagram of how to connect. So every one is trying to help each other.

You are using LEDs without resistors (always N.G.) The other guy's dwg shows a Trinket, not a Trinket [u]Pro[/u]. Perhaps you could pare back a bit and work with one LED, to make your breadboard photos a little easier to follow, and indicate where you're applying the battery.

I've added 330 ohm resistors to the board and it works as expected. I'm going to play a bit with the battery and see what I can figure out. Thanks again everybody for your patience and assistance! I've got a lot of reading and experimenting ahead of me!

EDIT: Just connected the battery pack as instructed and it works perfectly! My first mini-project is finally a success.