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WP34s Power Proc-Speed Performance
02-14-2015, 04:04 AM (This post was last modified: 02-14-2015 04:31 AM by MarkHaysHarris777.)
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RE: WP34s Power Proc-Speed Performance
(02-13-2015 11:35 PM)matthiaspaul Wrote:  One characteristic of this technology is that a cell consisting of two complementary MOSFETs draws measureable power only in state transitions, whereas in the static phases between these transitions, either one or the other transistor is always off (and the complementary one always on, respectively), so that no current can flow from supply to ground except for in those moments of state transition. So, the power consumption is a linear function of clock frequency - down to virtually zero when the clock is off.

Yes. This is measurable as well, with the setup above. At rest the current drain is virtually zero; I think I measured (not sure how accurately) something just less than 200 microAmps... 0.2 mA. During a square-root the current spiked quickly to 5 mA and quickly dropped back to zero. The CMOS gates are voltage logic... the high is tapped directly to Vcc, and the low is tapped directly to Grnd; no current flows except very briefly at transition; which is nice, because it allows us to power these hand-held super calculators with coin cells! The problem is that when the coin cells begin to die they still have a 'surface' voltage that reads near 3.0v, but which cannot sustain a 57 mW-minute. Marcus confirmed that the speed-stepping will try to auto-adjust up if it can; I think it should be designed so that if a shift down is necessary, it stays down! Consequently, I think its better to use the 'SLOW' function to set the frequency low from the get-go when we know that high current draw is going to be a problem.

PS Since I installed fresh cells the 2 second power-on delay has been corrected. I had a situation where the BATT reading was 2.9 (should have been high enough) but the system was losing power, forcing the power-on to reinitiate crystal calibration (Marcus knows the details).


Kind regards,
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RE: WP34s Power Proc-Speed Performance - MarkHaysHarris777 - 02-14-2015 04:04 AM

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