On May 5, 2009, at 6:44 PM, Rafael Enrique Ortiz Guerrero wrote: > These measurements are really cool. > > But the question remains in whether the ADC could have a resolution > of 1mv?, i mean in light of these measurements is necessary to have > an ADC that can reliable sense these variations and then with that > basis have a transfer function and add it to the algorithm.
Absolutely not. The A/D is eight bits, with an input range spanning 0 - 3.3V, so the best you can hope for is about 13 mV per LSB. I would guess actual accuracy to be closer to 26 mV. But why do you say you would need 1 mV accuracy ? Bright sunlight is far stronger than the light sources he used. > (haven't checked the specs though..) Having the data sheet for the EC controller doesn't help --- 8 bits and recommended operating voltage for the analog reference voltage is about all it provides. I had to ask a chinese speaker to call the app. engineer to find out the input impedance... > My two cents..;). > > Rafael Ortiz > > > On Tue, May 5, 2009 at 3:24 PM, Reinder de Haan <[email protected]> wrote: > Hallo, > > C. Scott Ananian wrote: > <snip> > > > A last resort would be hooking up a MOSFET as a simple amplifier -- > > again, you're not worried about linearity or any such niceties, but > > you'd still need a good match for your MOSFET's threshold voltage... > > some real measurements to replace the WAGes would go a long way. > > --scott > > > > measured on a B1 XO1 laptop (where the leds and the series resistor > are > wired in parallel it seam) : > > almost dark: 0mv > ~3meter away from a 8w PL; bare led: ~2mv > ~50 cm below ~25W halogen desk lamp; bare led: ~40mv > bright white led directly on bare led ~200mv > bright white led directly on light guide of the bat.led (lcd side) > ~50mv > ~50 cm below ~25w halogen desk lamp (~75* angle to the axis of the > light > guide) ~5mv > > i measure this between GND of the laptop the led side of the series > resistor. > all leds seam to be about the same.. i did not compare the different > light guides. > the main battery and DC power where removed, the RTC baterry was still > in place. > > > the meter i measured this with was fixed in the 2000mv range > and was abou 10Mohm when i connected it to another meter in resistance > mode; the (volt) meter read 250mv at that time. > > adding a 10Mohm resistor across the meter halved the > ~50 cm below ~25W halogen desk lamp; bare led: ~40mv reading to > ~20mv > > strangely enough when i add that resistor in series the meter said > ~60mv > so voltage on the leds must have been ~120mv? i will have to > investigate > this at a later time... > > if you want more measurement doen feel free to ask.. i also have a XO1 > (production model ?C1?) that i could measure. > > i dont have a lux meter :-( > > Greetings, > Reinder > > > > > > > > > _______________________________________________ > Devel mailing list > [email protected] > http://lists.laptop.org/listinfo/devel > > _______________________________________________ > Devel mailing list > [email protected] > http://lists.laptop.org/listinfo/devel _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
