Trellis, trinkets, power

[teeler]

Hi, (also, total noob warning)

I'm trying to figure out power requirements for a small project I'm doing with a trellis and a trinket.

Am I figuring this right? The trellis has 16 LEDs, so at 20mA each thats (16x20) 320mA, if all the LEDs are lit? So thats my maximum draw?

The trinket though, on the regulated voltage output pins can source a max of 150mA ... so I'm wondering, if I want to power
this with batteries, can I wire my batteries up in parallel to the trellis, just like what's done for these servos, in the rover project? (http://learn.adafruit.com/trinket-power ... lectronics, fritzing schematic at bottom)

But then I'm confused about the '5v' pin on the trellis actually means, also...do I *need* that source to be as close to 5v? In rover project for example, these servos are 5v (i think?), but the battery pack would only be producing 1.5v? Or do I have this all totally confused? EDIT: batteries wired in serial produce the sum of voltages? 3 AA's in serial would be 4.5V?

Any help would be greatly appreciated, thanks.

[adafruit_support_mike]

Am I figuring this right? The trellis has 16 LEDs, so at 20mA each thats (16x20) 320mA, if all the LEDs are lit? So thats my maximum draw?

Yep.

The trinket though, on the regulated voltage output pins can source a max of 150mA ... so I'm wondering, if I want to power this with batteries, can I wire my batteries up in parallel to the trellis,

Yes again. You need to connect GND on the Trellis to GND on the Trinket so they have a common reference point, but yeah, "this device gets its own battery" works.

But then I'm confused about the '5v' pin on the trellis actually means,

It means "connect the positive end of a 5v power supply here".

Or do I have this all totally confused?

That's another yes.

EDIT: batteries wired in serial produce the sum of voltages? 3 AA's in serial would be 4.5V?

Yep.. it's like putting three rulers end to end. They're each a foot long, but together they span a distance of three feet. Voltage is basically the 'electrical distance' between two points in a circuit.

[teeler]

Awesome - thanks Mike! One more question...

But then I'm confused about the '5v' pin on the trellis actually means,

It means "connect the positive end of a 5v power supply here".

Does it need to be exactly 5v, or will it operate under a range? I was currently planning on 3 AAA cells which would give me 4.5V, thats why I ask...I couldn't find any spec for the trellis, either.

[adafruit_support_mike]

It's a range, and to find the exact boundaries you kinda have to shuffle through the paperwork.

As a rule of thumb, you don't want to go more than about 0.25v higher than a listed value. You can burn chips out by connecting too much voltage, and if a device can handle more than the 'preferred' voltage, the maker will tell you about it. The Trinket's 'BATTERY +' pin can take up to 16v, for instance, so it's our job to tell people about it in the documentation: http://learn.adafruit.com/introducing-t ... uided-tour

Using too little voltage usually won't damage anything. If you're way too low, the device just won't work. If you're a little too low, things will mostly work but might not give you the best possible performance. Between those levels is a zone where you get all sorts of wierd behavior.

In this case, I know from experience that a 5v Trinket will run from a 3-pack of AAs connected to the GND and BAT+ pins, and the Trellis will also work on 4.5v. That's one of those slightly-off situations where asking is exactly the right thing to do. Ladyada/PT keep me around specifically to know stuff like that.

[teeler]

Thanks Mike! This is super helpful - I appreciate it.

[djwhouse56]

Any hope to run the Trellis in the 3 volts range??

[adafruit_support_mike]

Nope. The HT16K33 chip which does all the work wants a minimum of 4.5v.

[djwhouse56]

Thanks! I didn't see anything on the 'spec' pages for the device. Good to add operating voltages if they aren't there already. Great to know!

[djwhouse56]

I've looked around, but I have not been able to find a schematic for the 4x4 trellis board. My interest is primarily in the INT line, what it does, and how I might use it (does it need / have a pullup).

It looks like it's an indication of a button press? Schematic would be great!

[adafruit_support_mike]

It's an interrupt signal generated when the HT16K33 recognizes a pushbutton input.

Schematics for the Trellis are in our Github repo: https://github.com/adafruit/Adafruit_Trellis