Re: Ambient light sensing via LED response
The back-bias voltage is a sensitive topic. If you could guarantee periodic clearing of the integrator, I could provide up to 10V or so. Otherwise, it should probably be limited to +3.3V. wad On May 1, 2009, at 11:59 PM, John Watlington wrote: > On May 1, 2009, at 2:28 PM, C. Scott Ananian wrote: > >> On Tue, Apr 28, 2009 at 8:38 PM, John Watlington >> wrote: >> > I don't have time to take a look at this right now, >> > but we have a A/D input to dedicate to this, if it helps work >> around >> > the patent. >> > >> > We can talk to MERL if needed. I probably still know a handfull >> > of people around there. >> >> Oh, yeah, you should be able to wire the top side of the LED >> directly to the LED and measure the photovoltaic current directly; >> that's not patented: >> battery voltage >> Q1 | >> ---from EC--|< _ to A/D >> | >> LED V >> | >> GND >> >> The only question is whether the LED can put out enough >> photovoltaic current to be reliably measured by the A/D. > > Ahh, therein lies the challenge! > >> Depends on what the input to the A/D looks like, how much >> capacitance it sees, etc. > > Thought the KB3700 (EC) A/D datasheet frustratingly doesn't list > any such exotic parameter > as input impedance, I asked ENE and they said that the input was > high impedance CMOS > (think a MOSFET gate, in the wee, wee microamps). The impedance > also does not vary > (even though the A/D is muxed). > >> An ultralow power versoin of the 339 could fix any problems there, >> but then your parts count increases. > > Sorry, no parts count increases allowed except for one LED, > resistors, capacitors (basically free), and maybe > one transistor, diode, or NMOS MOSFET (about a penny). I will > throw in a couple of EC digital outputs, and > a day of Richard's time in EC code. > >> You don't *have* to reverse-bias the LED; that just enhances >> sensitivity, but distinguishing between >> "outside on a sunny day" and "inside" doesn't exactly require >> precision; there's at least an order of >> magnitude change in illumination, maybe 2 (http://en.wikipedia.org/ >> wiki/Lux). > > I haven't read the patent, but the advantage to a digitally > controlled time integration A/D has always > been a high dynamic range by changing the time scale. I'll let the > community suggest this > circuit/algorithm. Someone practiced in the arts might suggest > measuring the integration of > the reverse leakage current over time, using a digital output to > clear the integrator, allowing > software to control the time period over which the current is > integrated to increase the range. > > In response to earlier mails on this topic: the microphone/camera > LEDs are inviolate. > ( Ivan got this one right! ) I will not allow software > interference with those LEDs. > > The power savings resulting from switching the LEDs was significant > in Gen 1 (on the order of > 50 mW in run/suspend). Even after adding this feature, it will > have to be integrated into Ohm > and the Control Panel before being useful in power savings. > > By the way, has anyone really thought about this feature ? I grok > the intent, but you have to make > sure that kids who happen to be in brightly lit rooms (glaring > fluourescents aren't uncommon) > don't loose their backlight, and wonder why ? The keyboard > lighting on my mac is a good idea, > but they only allow adjusting the amount of light output, not the > sensitivity to ambient light. > > And the Mac's light sensor is annoyingly placed where hand movement > during typing may occlude it, > something we should be able to avoid... > The light pipes for most LEDs, however, are quite large. I believe > that a second LED > could be positioned next to an output LED, under a light pipe. > Perhaps the battery LED is > the best candidate, since it is usually not lit when operating from > the battery. > > Cheers, > wad > ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Ambient light sensing via LED response
On May 1, 2009, at 2:28 PM, C. Scott Ananian wrote: > On Tue, Apr 28, 2009 at 8:38 PM, John Watlington > wrote: > > I don't have time to take a look at this right now, > > but we have a A/D input to dedicate to this, if it helps work around > > the patent. > > > > We can talk to MERL if needed. I probably still know a handfull > > of people around there. > > Oh, yeah, you should be able to wire the top side of the LED > directly to the LED and measure the photovoltaic current directly; > that's not patented: > battery voltage > Q1 | > ---from EC--|< _ to A/D > | > LED V > | > GND > > The only question is whether the LED can put out enough > photovoltaic current to be reliably measured by the A/D. Ahh, therein lies the challenge! > Depends on what the input to the A/D looks like, how much > capacitance it sees, etc. Thought the KB3700 (EC) A/D datasheet frustratingly doesn't list any such exotic parameter as input impedance, I asked ENE and they said that the input was high impedance CMOS (think a MOSFET gate, in the wee, wee microamps). The impedance also does not vary (even though the A/D is muxed). > An ultralow power versoin of the 339 could fix any problems there, > but then your parts count increases. Sorry, no parts count increases allowed except for one LED, resistors, capacitors (basically free), and maybe one transistor, diode, or NMOS MOSFET (about a penny). I will throw in a couple of EC digital outputs, and a day of Richard's time in EC code. > You don't *have* to reverse-bias the LED; that just enhances > sensitivity, but distinguishing between > "outside on a sunny day" and "inside" doesn't exactly require > precision; there's at least an order of > magnitude change in illumination, maybe 2 (http://en.wikipedia.org/ > wiki/Lux). I haven't read the patent, but the advantage to a digitally controlled time integration A/D has always been a high dynamic range by changing the time scale. I'll let the community suggest this circuit/algorithm. Someone practiced in the arts might suggest measuring the integration of the reverse leakage current over time, using a digital output to clear the integrator, allowing software to control the time period over which the current is integrated to increase the range. In response to earlier mails on this topic: the microphone/camera LEDs are inviolate. ( Ivan got this one right! ) I will not allow software interference with those LEDs. The power savings resulting from switching the LEDs was significant in Gen 1 (on the order of 50 mW in run/suspend). Even after adding this feature, it will have to be integrated into Ohm and the Control Panel before being useful in power savings. By the way, has anyone really thought about this feature ? I grok the intent, but you have to make sure that kids who happen to be in brightly lit rooms (glaring fluourescents aren't uncommon) don't loose their backlight, and wonder why ? The keyboard lighting on my mac is a good idea, but they only allow adjusting the amount of light output, not the sensitivity to ambient light. And the Mac's light sensor is annoyingly placed where hand movement during typing may occlude it, something we should be able to avoid... The light pipes for most LEDs, however, are quite large. I believe that a second LED could be positioned next to an output LED, under a light pipe. Perhaps the battery LED is the best candidate, since it is usually not lit when operating from the battery. Cheers, wad ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Ambient light sensing via LED response
On Fri, May 1, 2009 at 2:28 PM, C. Scott Ananian wrote: > Oh, yeah, you should be able to wire the top side of the LED directly to > the LED and measure the photovoltaic current directly; that's not patented: > battery voltage > Q1 | > ---from EC--|< _ to A/D > | > LED *V* > | > GND > > The only question is whether the LED can put out enough photovoltaic > current to be reliably measured by the A/D. Depends on what the input to > the A/D looks like, how much capacitance it sees, etc. An ultralow power > versoin of the 339 could fix any problems there, but then your parts count > increases. You don't *have* to reverse-bias the LED; that just enhances > sensitivity, but distinguishing between "outside on a sunny day" and > "inside" doesn't exactly require precision; there's at least an order of > magnitude change in illumination, maybe 2 ( > http://en.wikipedia.org/wiki/Lux). > A reverse biased LED doesn't output much current at all - even photo sensor diodes that are tuned for the job. Have a look at this page for some ambient light sensors that you would find in a cell phone - http://www.avagotech.com/pages/en/optical_sensors/ambient_light_photo_sensors/light_sensor_photo_sensor/. The basic variety has a photodiode and a small current amplifier. The output current is logarithmically related to the lux level. If hook a series resistor to the output, the voltage across vs lux is also logarithmic. Besides the current amplifier, these devices have other advantages. First, they have a spectral sensitivity that's tuned to the human eye, so infrared light (say a campfire) will not skew the reading. Second, they have a large optical window so the readings won't change when you tilt your phone/laptop slightly. These little sensors are less than $0.25 in large quantities (perhaps by quite a bit), and they are being used more and more in cell phones to reduce backlight power in low light environments. It's well worth the price if you get 10% more battery life on average. Quantifying the impact on battery life is tricky because there are a lot of assumptions. Anyways, a normal LED might work under certain circumstances. I don't have the experience to say one way or another. Thanks, Nate ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: [support-gang] 2PM EDT Friday: BRIEF Contributors Program Mtg (#olpc-meeting)
Sorry also not able to keep up recently. Had a baby boy (7 lbs. 14 oz.) last week and have been wanting to get re-connected. But have been following the emails while catching up at work. Keep up the good work! Aaron On May 1, 2009, at 11:46 AM, Holt wrote: In 15min from now! Join us reviewing the latest OLPC/Sugar community projects today 2PM EDT, Boston Time: http://forum.laptop.org/chat Then type at bottom: /join #olpc-meeting AGENDA: * New Libraries! http://wiki.laptop.org/go/Projects#XO_Laptop_Lending_Libraries * Which projects might you enjoy Mentoring?! http://wiki.laptop.org/go/Projects http://rt.laptop.org/Search/Results.html?Query=Queue=%27contributors%27 * Fast Review of the 2 latest (greatest!) HW/Project Proposals: 1. Gaza Beach Art [Austria] http://rt.laptop.org/Ticket/Display.html?id=39345 http://www.gazabeach.at Requests 1 XO for 5 months Project Objectives: Titel: Gaza Beach: We Join the Party – public art intervention Background On the occasion of Tel Aviv's centennial, the city of Vienna has invited the state of Israel to stage part of its celebrations at a beach at the Danube Canal. Under the title „Gaza Beach – Life Imprisonment Live“, sever al intervention projects will simultaneously be staged in public spaces. They are aimed at directing as much attention to Palestine as to Israel for the duration of the „Tel Aviv Beach.“ Our project is aimed at helping to create an authentic atmosphere and to enable the cooperation between Tel Aviv and its nearest partner city: Gaza in a neutral environment. 2. Audubon MS XO Library and Repair Center [Los Angeles, Calif, USA] http://rt.laptop.org/Ticket/Display.html?id=39449 http://wiki.laptop.org/go/Projects#XO_Laptop_Lending_Libraries Requests 10 XO's for 24 months Set up an XO laptop lending library for the 50 students enrolled in the Vista College Bound/Famili After School Program Show that an XO lending library run by and for middle school students is a viable option Identify Sugar Activities most suitable for use in an after school academic enrichment program Develop students’ ability to make simple repairs to the laptops a s the need arises ___ support-gang mailing list support-g...@lists.laptop.org http://lists.laptop.org/listinfo/support-gang ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: [support-gang] 2PM EDT Friday: BRIEF Contributors Program Mtg (#olpc-meeting)
On Fri, May 1, 2009 at 11:22 AM, Aaron Hull wrote: > Sorry also not able to keep up recently. Had a baby boy (7 lbs. 14 oz.) > last week and have been wanting to get re-connected. But have been following > the emails while catching up at work. Keep up the good work! > Aaron > Congratulations! Finally, something productive :-) Just kidding. Post some pics. Make him pose with an XO! I couldn't make it to the meeting either...faculty meetings :-( Sameer -- Dr. Sameer Verma, Ph.D. Associate Professor of Information Systems San Francisco State University San Francisco CA 94132 USA http://verma.sfsu.edu/ http://opensource.sfsu.edu/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Ambient light sensing via LED response
On Tue, Apr 28, 2009 at 8:38 PM, John Watlington wrote: > I don't have time to take a look at this right now, > but we have a A/D input to dedicate to this, if it helps work around > the patent. > > We can talk to MERL if needed. I probably still know a handfull > of people around there. Oh, yeah, you should be able to wire the top side of the LED directly to the LED and measure the photovoltaic current directly; that's not patented: battery voltage Q1 | ---from EC--|< _ to A/D | LED *V* | GND The only question is whether the LED can put out enough photovoltaic current to be reliably measured by the A/D. Depends on what the input to the A/D looks like, how much capacitance it sees, etc. An ultralow power versoin of the 339 could fix any problems there, but then your parts count increases. You don't *have* to reverse-bias the LED; that just enhances sensitivity, but distinguishing between "outside on a sunny day" and "inside" doesn't exactly require precision; there's at least an order of magnitude change in illumination, maybe 2 (http://en.wikipedia.org/wiki/Lux). --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: CL1B power distribution
On Fri, 1 May 2009, Benjamin M. Schwartz wrote: > John Watlington wrote: >>> the LED trick has the advantage of not requiring a change to the case, >>> just a single additional drive pin to be able to run it as a detector. >> >> And where would you place said detector LED, without modifying the >> case ? > > While we're bikeshedding this to death, I'll put in my vote for reusing > the camera activity LED. It's well isolated from other light sources, and > it's rarely on. Whenever the camera is off, it can be used a > photodetector. To retain the security guarantee that the light is on when > the camera is on, it might be necessary to put a diode across the camera's > power supply, so that they can be reverse-biased together. my understanding is that currently the camera and mic LEDs are hard-wired to those devices, not controlled independantly (to make sure that it's not possible to activate those devices without activating the LED) the power LED is well seperated from everything else, has a fairly large opening in the case to let light in, so it would seem to be a good option. at least one article indicated that this could be done with an LED that was otherwise on without the user noticing (comments were made that in the dark the delay could become noticable, but that could be solved by setting a max count to wait for) David Lang > If only we could get another hole in the case. ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: CL1B power distribution
On Fri, 1 May 2009, Jameson Quinn wrote: I like the idea, but wouldn't light transmission inside the case, from the other LED's, screw this up? possibly, how much leakage is there between the LEDs? David Lang (btw, wikipedia says more light = faster backwards discharge) Heck, the two separate wireless LEDs cause more confusion then they're worth anyway, you might as well get rid of one and use the LED there only for input... +1 ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: CL1B power distribution
John Watlington wrote: >> the LED trick has the advantage of not requiring a change to the case, >> just a single additional drive pin to be able to run it as a detector. > > And where would you place said detector LED, without modifying the > case ? While we're bikeshedding this to death, I'll put in my vote for reusing the camera activity LED. It's well isolated from other light sources, and it's rarely on. Whenever the camera is off, it can be used a photodetector. To retain the security guarantee that the light is on when the camera is on, it might be necessary to put a diode across the camera's power supply, so that they can be reverse-biased together. If only we could get another hole in the case. --Ben signature.asc Description: OpenPGP digital signature ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: CL1B power distribution
I like the idea, but wouldn't light transmission inside the case, from the other LED's, screw this up? (btw, wikipedia says more light = faster backwards discharge) Heck, the two separate wireless LEDs cause > more confusion then they're worth anyway, you might as well get rid of > one and use the LED there only for input... +1 ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: CL1B power distribution
On Tue, Apr 28, 2009 at 8:51 PM, John Watlington wrote: > > All of our LEDs are dual (one on the inside and one on the outside). > Instead of running these in parallel, and throwing away the extra > voltage, I run them in series directly from the battery voltage > (ever notice that their brightness changes when you plug in > the charger ?) Is this a change to the Gen 1 design? I remember studying the Gen 1 schematic and convincing myself it could be done if only we could run an additional wire to an input pin. You don't have to drive the LED directly from the microcontroller; you only need to be able to switch it and sense the voltage while watching the time. The photocurrent causes the inherent capacitance to discharge faster (or slower? I forget). The time scale is really short, but that's no problem for today's chips. You could parallel a (very small) capacitor across the LED to "make it more sensitive". Any of the four existing LEDs would be appropriate: wireless "A" and "B", battery, or power. Heck, the two separate wireless LEDs cause more confusion then they're worth anyway, you might as well get rid of one and use the LED there only for input... --scott -- ( http://cscott.net/ ) ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
2PM EDT Friday: BRIEF Contributors Program Mtg (#olpc-meeting)
In 15min from now! Join us reviewing the latest OLPC/Sugar community projects today 2PM EDT, Boston Time: http://forum.laptop.org/chat Then type at bottom: /join #olpc-meeting AGENDA: * New Libraries! http://wiki.laptop.org/go/Projects#XO_Laptop_Lending_Libraries * Which projects might you enjoy Mentoring?! http://wiki.laptop.org/go/Projects http://rt.laptop.org/Search/Results.html?Query=Queue=%27contributors%27 * Fast Review of the 2 latest (greatest!) HW/Project Proposals: 1. Gaza Beach Art [Austria] http://rt.laptop.org/Ticket/Display.html?id=39345 http://www.gazabeach.at Requests 1 XO for 5 months Project Objectives: Titel: Gaza Beach: We Join the Party -- public art intervention Background On the occasion of Tel Aviv's centennial, the city of Vienna has invited the state of Israel to stage part of its celebrations at a beach at the Danube Canal. Under the title "Gaza Beach -- Life Imprisonment Live", several intervention projects will simultaneously be staged in public spaces. They are aimed at directing as much attention to Palestine as to Israel for the duration of the "Tel Aviv Beach." Our project is aimed at helping to create an authentic atmosphere and to enable the cooperation between Tel Aviv and its nearest partner city: Gaza in a neutral environment. 2. Audubon MS XO Library and Repair Center [Los Angeles, Calif, USA] http://rt.laptop.org/Ticket/Display.html?id=39449 http://wiki.laptop.org/go/Projects#XO_Laptop_Lending_Libraries Requests 10 XO's for 24 months Set up an XO laptop lending library for the 50 students enrolled in the Vista College Bound/Famili After School Program Show that an XO lending library run by and for middle school students is a viable option Identify Sugar Activities most suitable for use in an after school academic enrichment program Develop students' ability to make simple repairs to the laptops as the need arises ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: I2C bus assignments
I have a bad feeling about swiping the CRT I2C. It kind of leaves a needless landmine for video driver authors who would prefer to unify their code (XO and non-XO hardware) as much as possible. Suppose a video driver attempts E-DDC. Is it going to confuse some non-compliant I2C device or actually hit the address in use? Bit banging the DCON sounds OK. Your comment about the DCON bug makes this appealing, but is also worrisome. Is this not fixed in current chips? (if not fixed, and you do decide to fix it, please also make the two image quality fixes I requested) You didn't mention bit banging the camera. If you're bit banging anyway, the fact that the camera isn't correct I2C is no issue. (please tell me I2C is for control only, not streaming video) You didn't mention bit banging the clock generator. Impossible? ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
