Bilge Tank 116 Micro Bit


#1

I was just watching the Micro Bit Bilge Tank video on the Micro Bit, I have a caution that I think needs mentioning. When powered via USB your limited to 120ma, which may be why some of the demos didn’t work so well. The limit is because of the 5V to 3V regulator on the Micro Bit, see here in the power supply section, http://tech.microbit.org/hardware/#power-supply
However, if you use a battery pack connected to the JST jack, you won’t hit that limit as your not using that regulator anymore. The 3V bus comes right from the battery + contact. Just make sure you only apply 3V, two double A or triple A battery’s etc. Do not connect a LIPO battery as that will damage the Micro Bit, 3.6V is the max. Caution is still advised if connecting motors etc, you don’t want to sink too much current through the Micro bit inputs. IMHO you’ll have much better results with projects if you run from a battery pack.


#2

This is a good point. We’ve taken this into account and tested it for boards like scroll:bit, which adheres to the limits, but for things like pin:bit where the end-user can connect any madness they desire we’ll just have to make sure this is communicated clearly in documentation. /me summons @tanya


#3

I first ran into it with the Micro:Pixel Edge. On battery it works fine, on USB not so much. If I kept the brightness low it was OK on USB.
Same sort of thing happened when I played with a servo. Didn’t work from USB but was fine when on battery. I do believe anything wired to the 3V and Ground pins gets the power from the battery pack, if its connected. Like a servo for example. And control signal comes from the Micro Bit. No real danger of drawing too much current from the Micro Bit unless you short something out.
One thing I don’t know, is what happens if you draw too much current from the regulator. Can you damage it? I try to make it a habit to not have anything attached to my Micro-Bit when uploading code via USB. I have the bread:bit for bread board connection. Your version wasn’t available at the time I bought mine.


#4

IIRC te Micro:Pixel documentation explicitly warns you not to drive the pixels too bright, or they’ll draw too much power. Not exactly the best approach for something supposed to be child-friendly. With 10 pixels at a hypothetical 20mA per element that’s a whole 600mA peak current draw which is just a tad over the micro:bit’s budget :D

We have been careful to keep power budgets within the documented limits for micro:bit, or at least very, very close. The regulator can certainly deliver more current but it gets hot and eventually the micro:bit becomes pretty unstable.

Servos are a pain- they don’t need all that much current once they’re moving, but need a big spike when they start up. This is why Flotilla doesn’t have a servo board, try as we might we couldn’t get it to work within our power budget.

You could certainly damage the regulator, but how far you can push it will vary. I think the much more immediate risk is of you physically hurting yourself on a hot component. (which I did during some early testing, ow!)


#5

I remember discussing current draw with the Micro Pixel with you when I first got it and my first Micro Bit. That’s when I started looking at the spec sheet for the Micro bit.
If it ever warms up around here I’d like to take my Micro Bit and attachments out on my deck to play with. I have the Bread Bit, bread board, speaker and one of the Sidekick components packs to play with. I actually have 2 of everything I just listed. I have a nice big table and a shaded gazebo. I want to try a few things to maybe get one or more of my grand kids interested and then let them have a go with one of them.
I bought a couple of the 3 AA battery packs and soldered male headers to the leads to make it easy to plug them into a bread board. My plan is to use that as the power for servos etc, and only connect the signal and ground to the Micro Bit. That’s my plan anyway.


#6

That Gator Bit looks interesting, and maybe a way around the current limit restriction? I haven’t delved into the actual specs yet but the 5V and 3V out looks like a cool feature. It’s not cheap but it looks like there is a lot on it.

EDIT: It looks like up to 1.5A on the 3V and 3.6 on the 5V, but the 3V is feed from the 5v out?