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From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: comp.windows.misc,comp.sys.next,comp.sys.mac
Subject: Re: replacing the desktop metaphor
Keywords: desktop metaphor, graphical interfaces, computing environments
Message-ID: <17955@glacier.STANFORD.EDU>
Date: 31 Dec 88 18:13:44 GMT
References: <4362@pitt.UUCP> <257@gloom.UUCP> <82702@sun.uucp> <8939@ut-emx.UUCP> <3504@geaclib.UUCP> <18640@agate.BERKELEY.EDU> <18655@agate.BERKELEY.EDU>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University
Lines: 23

In article <18655@agate.BERKELEY.EDU> c60a-2di@e260-2d.berkeley.edu (The Cybermat Rider) writes:
>I know from personal experience (with IR remote controls, no less) that IR
>LEDs draw just a little power, and even considering the number of characters
>transmitted during an average session, I'm sure it wouldn't be too difficult
>to develop a battery pack that would allow activation of an IR LED at least
>10 billion times.

      Well, let's see.  Typical LEDs draw 20-100 mA at 5v.  Let's use 25mA
as a working figure.  Assume 1200 bit/sec transmission from a keyboard, and
that each character transmitted requires 12 bits (startup, framing, redundancy,
and shifts.)  So we take 10ms per character typed.  Each keystroke thus
uses 0.25ma/sec or 7 x 10^-8 ampere-hour.  NiCd batteries run about 0.1
ampere-hour in AA size.  So 3 AA NiCd batteries should be good for about 1.4
million keystrokes, not counting any power consumption in the remainder of
the electronics.  If we assume an average keying rate of 2 keystrokes/second,
we have an operating life of 200 hours.  

      These are very optimistic assumptions.  We've ignored any power
consumption from the rest of the system, and may want to use more power
than 25mA.  If we want to use diffuse infrared, bouncing off walls,
rather than requiring line-of-sight, 500mA would be more realistic.

						John Nagle