godFather89 wrote:In other topics I described that I removed the onboard USB hub (+ethernet). I also removed the 3.3V linear regulator. Actually I replaced it with a switch mode regulator (higher efficiency) and added a Li-Ion battery (from a phone), a charger IC and a power switch. So now my Pi is powered from the battery (4.2V max) and the battery is charged from the lapdock. In this way, the Pi will not restart anymore when the lapdock lid is closed.
I also did some power measurements and my Pi draws 0.504W (120mA) when idle.
That .504watt is pretty low. Someone had a thread where they tested the production RasPi at 2watts resting. The Alphas were at 350watts resting or so and 1watt running full out. .
Something is seriously wrong with these numbers.
From everything I've experienced and others have reported, there's no way a Pi can run on 4.2 volts at the supply input - none, nada, zip. Where/how was this measured?
Measuring power is a tricky proposition because you have to measure both voltage and current together instantaneously. I don't see in the photos where you're measuring both at the same time. Plus, meters perform averaging, whether they're analog or digital, so, you can't really state accurately what the actual power is on such a complex device as a computer without using storage oscilloscopes or digital signal processors/analog-to-digital converters (one for voltage and another for current). Power consumption fluctuates by sub-microseconds, depending on what's being executed at any given moment, and this is especially true when power levels are as low as they are with the Pi.
350 watts? Waaaaatt??? Obviously, you meant 350 milliwatts (mw), or 0.350 watts (that's why engineers include the leading zero before the decimal point
). We all know this, but, I'm pointing this out for folks who may be trying to learn from us. It's bad enough when we get sloppy with programming, but, data, especially physical data measurements, need to be measured and reported precisely, or they tend to take on a life of their own. Few people have the knowledge, experience, and equipment needed to do it right, so, we need to be extra careful what we measure and report as ideal examples to the students following our work.
Once I get everything tucked into my below-lapdock case, I'll make some measurements with voltage and current recording equipment in the EE lab that's appropriate for this sort of thing. I'll see if I can figure out how to coordinate the recordings with what's actually running on the Pi at any given point in time (e.g., output from the Linux "top" utility). I'm not sure how I'll get timestamps so the voltage/current data can be correlated with the running processes.
Other than that, everything else went fine at the theater, Mrs. Lincoln!
The best things in life aren't things ... but, a Pi comes pretty darned close!
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!