CL1B power distribution

James Cameron quozl at
Sun Apr 26 20:02:13 EDT 2009

On Sun, Apr 26, 2009 at 12:40:14AM -0400, Benjamin M. Schwartz wrote:
> Turning off a single port to which nothing is connected saves no power,
> right?  I don't see the appeal.  [...]

Sorry, perhaps I didn't explain myself adequately.

One of the uses of the laptop is in teaching of electronics and control
systems.  The current model has an analog input on the microphone
socket, but digital outputs require the addition of external USB
devices [1].

If there is a way to switch the 5V supply to individual USB ports, and
if that was exposed in software ... and it is $0.15, then the question
isn't really "what power will it save" but rather "does the potential
use justify the cost?"

The USB ports could then be used as switchable 5V sources, with the
current driving external devices directly, with the data leads of the
USB cable disconnected.

I don't know of anyone who plans to teach electronics and control
systems though.


[1] the analog input can be used as a digital output with additional
circuitry that detects the switching of the bias voltage, but that is
quite complex for a student to comprehend.

James Cameron    mailto:quozl at

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