Phil Spiegel said:
My first reply to this double-posted topic vanished into thin air -along with the 2nd copy!
Whereas a phone is optimised in its design to save power and work from a 3.6V Lithium battery, for as long as possible; switching off unused parts, for example, its peak power consumption would only be for the short times when it is transmitting in a poor signal area, with the screen active.
(Note how they blank the screen when your phone is 'held to the ear')
The Pi design assumes that if it is powered; it is because you are using it: it will not blank the screen if you glance away, or slow its processing. The Pi is powered from a continuously available external 5V: (700mA minimum capability)
Therefore an economy to meet the 25$ cost was to use a LINEAR regulator from 5V external supply to 3.3v etc..
However: at 700mA maximum current (rare on a phone, but possibly continuous on the Pi) P=IV : Power lost in the regulator = 0.7A x 1.7V (approx) =1.2W ... close to equalling that of the 'Pi itself'
This might be an area where the increased buying power of RS+Farnell might allow a pin-compatible switched-mode regulator to fitted - thus helping save the world's energy (by scrapping thoise old PCs) - and be more flexible on battery voltage!
I believe Gert is intending to provide instructions on how to change the power regulator to something more efficient. It is the weak link in the power chain. The GPU only uses about 8mW when not doing anything (which in the OP's case sounds likely) - not sure about the Arm though. Depends how good the Linux power management is, and I don't know anything about that.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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