[nSLUG] Powering a RPi (was Re: Cellular dongles)

Joel Maxuel j.maxuel at gmail.com
Mon May 27 22:18:41 ADT 2019

On Mon, 2019-05-27 at 14:30 -0300, Dave Flogeras wrote:
> On Mon, May 27, 2019 at 1:44 PM Joel Maxuel <j.maxuel at gmail.com>
> wrote:
> >  Interestingly enough, I discovered one of those conclusions
> > earlier today with the MoPi2 (paired with the stacking header):
> > https://pi.gate.ac.uk/pages/mopi.html  
> > 
> > ...which will allow up to 2.5A (given if each peripheral peaks at
> > the same time - that can still leave 960mA) for the Pi.
> > 
> That's the one I couldn't remember earlier!  Make sure you read up on
> any candidates, there is always a varying degree of quality/support. 
> Some of these products are just pet projects, with no intention of
> doing proper software/kernel level support after it is released. 
> YMMV.  IIRC I evaluated a Pimoroni E-Paper board, and while it did do
> what it said it would, it wasn't integrated in any way to the
> operating system; just some hacks and python scripts to communicate
> with it.  Same went for the early Wolfson audio boards, unsupported
> bash nonsense and user daemons in lieu of a proper driver (which the
> community has since created).

I hear that.  The MoPi2 documentation seems quite complete except ...
the device comes with a charge gate terminal pair if you want to
control charging of one of the voltage inputs (say 8 x 1.2V NiMH AA
cells - picking on this scenario as it is their default).  I am having
difficulty in finding a corresponding charging circuit aside from a
couple circuit sketch-ups for other scenarios (for use in a vehicle;
for connecting a Li-Po battery) and seemingly impossible for an off-
the-shelf companion for their software default.

An annoying outcome since this was featured in the shortlist of an
Instructables article, and most in that list (how to power a RPi) were
not floating something third party.  

> >  
> > > And this way you could position your board between the pi and
> > > Razberry2.  You could break out the supply pins, and any other
> > > peripherals for any customization you need (UART, I2C for
> > > realtime clock....).  It's pretty cheap to get PCBs made up at
> > > OSHPark and if you have a couple random circuits, it can greatly
> > > clean up your project.  When you're getting closer, I'd be happy
> > > to show you enough KiCad to make you dangerous.
> > > 
> > 
> > Not sure how important that detail will be, as the finished product
> > will be in my basement (likely mounted to the wall in a panel
> > box).  You mentioned breakout for an RTC - is internal time-keeping 
> > that bad, or just plain non-existent?
> > 
> > 
> The Pis don't include an RTC, probably to save a bit of BOM cost/real
> estate of having a coin cell on board.  It's easy enough to add one;
> I've spit rolled my own but I would imagine kits are readily
> available by now.  Most people don't care, since typically they are
> always connected to get NTPD to update the clock.  In my experience,
> the internal clock doesn't skew more than your average PC.

Oh,that makes more sense.  Yeah, that won't bother me.  I
misinterpreted it as it would not be unable to tell time if it didn't
have constant network access.

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