Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!tut.cis.ohio-state.edu!uc!noc.MR.NET!gacvx2.gac.edu!hhdist From: robert@longs.LANCE.ColoState.Edu (Robert D. Thompson) Newsgroups: comp.sys.handhelds Subject: RE: HP28 power study Message-ID: <9012040556.AA19531@longs.LANCE.ColoState.Edu> Date: 4 Dec 90 05:56:13 GMT Lines: 77 To: handhelds@gac.edu Return-path: In-reply-to: Your message of Sat, 01 Dec 90 18:27:00 -0600. To: handhelds@gac.edu > Relay-Version: VMS News - V6.0 13/10/90 VAX/VMS V5.4; site gacvx2.gac.edu > Path: gacvx2.gac.edu!noc.MR.NET!msi.umn.edu!src.honeywell.com!sol.ctr.columb ia.edu!emory!swrinde! > zaphod.mps.ohio-state.edu!usc!snorkelwacker.mit.edu!mit-eddie!uw-beaver!mil ton!ogicse!orstcs!usenet!ECE.ORST.EDU!daver > Newsgroups: comp.sys.handhelds > Subject: Re: HP28 power study > Message-ID: <1990Dec01.224400.11957@scion.CS.ORST.EDU> > From: daver@ECE.ORST.EDU (Dave Rabinowitz) > Date: 1 Dec 90 22:44:00 GMT > Sender: @scion.CS.ORST.EDU > References: <3017@gmuvax2.gmu.edu> > Organization: Oregon State University -- Electrical & Computer Engineering > Nntp-Posting-Host: ece.orst.edu > Lines: 76 > > In article <3017@gmuvax2.gmu.edu> peraino@gmuvax2.gmu.edu (Bob Peraino) writ es: > >A few people have asked how much power can be saved if the operating speed > >were set to 0, and the display were turned off. We can now calculate this. > >From the above power chart, we see that speed 7 draws 2399 uAMPS and speed > >0 draws 1633. Combined with disabling the display at minimum contrast, this > >is a savings of (2399-1633)+243 = 1009, or about 42% of the normal operating > >current. > [ Stuff Deleted ] > This is not a surprising result. Actually it is > The hp28s is implemented in CMOS, so for > digital operations there is no DC power I would really like to see this CMOS design!! > (there is DC power in the analog > circuits which generate the display voltages, generate the CPU clock and > check the battery condition, etc.). Each operation requires charging and > discharging capacitances, and the same capacitances go through the same > charge and discharge cycles to execute the same operations regardless of > operating speed. Therefore, you can think in terms of capacitance charges > per operation. It turns out that the power dissipated in charging a > capacitor from a given voltage to another voltage is the same regardless > of how fast the capacitor is charged, so each digital operation takes the > same amount of energy regardless of how fast the operation is performed > (obviously this breaks down if you go too fast or too slow, but this is > accurate within the available speeds). Running the calculator faster takes > the same amount of energy to do the digital operations as running it slower, > but since less total time is taken, there is less overhead energy lost to the > analog circuits so the total energy consumption is less. So basically you are sayin that the HP-28 is an analog computer of sorts. I beg to differ !!! In fact CMOS typically demands more power at higher clock frequencies. This can be seen by looking at the spec sheets for a simple CMOS gate. Furthermore, the capacitors used to drive the display (for instance) have no relevance here. They play *NO* part in the performance of the math functions available in the calculator and as such have no role in the consumption of power when considering the execution of a program, for example. The power thay consume, or rather the driving circuitry, is dependent on such things as display contrast, battery voltage, temperature, etc. Lets get some background information before we release -Robert ------------------------------------------------------------------------------- Department of Electrical Engineering | "If you are going to say it, Colorado State University | check the facts..." | Center for Computer AssiSted Engineering | robert@longs.LANCE.ColoState.Edu Colorado State University | -------------------------------------------------------------------------------