Re: Ambient light sensing via LED response

2009-05-01 Thread Nate Ridderman
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*

 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 (

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 -
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.

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Re: CL1B power distribution

2009-04-25 Thread Nate Ridderman
Any chance of getting schematics and PCB files this time around? I doubt you
renegotiated your contract with Quanta to allow for this, but it doesn't
hurt to ask.


On Sat, Apr 25, 2009 at 12:23 AM, John Watlington wrote:

 BTW, Gen 1.5 is the OLPC codename for the next revision of the XO.

 The official Quanta model number for the XO was CL1.
 The version of the XO with a new touchpad is CL1A.
 The Quanta model number for Gen 1.5 is CL1B.


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Re: CL1B power distribution

2009-04-25 Thread Nate Ridderman
On Sat, Apr 25, 2009 at 10:05 AM, wrote:

 smith wrote:
Additional changes from Gen 1 include the ability to both measure
DC input current and VIN voltage, as well as EC control over the
current drawn from the DC input. The intent was to better support
charging directly from solar panels.
I hope that this will be available to activities like Measure.

 (will an XO even run properly from an unrectified, or even
 unfiltered, supply?)

Sure, if the right circuit is in place. A solar panel is rectified, which
makes things easier, but the power and voltage output is variable. It sounds
like Gen 1.5 will have charging FETs that you can gradually turn on/off to
limit the current flow through a path. Therefore, you can shut it off when
the charger isn't producing enough voltage or too much voltage for the
battery. It's hard to know exactly what's going on without seeing a
schematic and/or datasheet of the parts involved.

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Re: View Slides is in

2009-02-03 Thread Nate Ridderman
There was an email thread about problems with not long ago
- see I
was having the same problem and I sent an email to
I'm not sure if it was ever resolved for my account, because I haven't tried
it yet.


2009/2/3 James Simmons


 The current View Slides sends the whole slideshow in a Zip file over the
 network.  These slideshow Zip files can be 20-60 meg and I find that sharing
 files of that size just doesn't work.  Worse, if the original file is still
 being shared it is impossible to resume a document you have received by
 sharing without starting the whole download over again.  So I think my new
 idea makes a lot more sense, and I'm thinking I can use code in Chat as an
 example to work from.

 I have moved both my repositories to gitorious:

 However, last night and this morning when I tried to do a git push to the
 new repository I got this:

 [...@localhost ~]$ cd olpc/readetexts/mainline/
 [...@localhost mainline]$ ls
 activity  NEWS   ReadEtextsActivity.pyc
 MANIFEST  readtoolbar.pyc
 [...@localhost mainline]$ git push origin master
 fatal: The remote end hung up unexpectedly

 This is on a machine where I have never done a git push before (I did my
 development work on a different box).  I created my SSH key and published
 the public key in the account named jdsimmons, along with the other public
 key from the other box.  I just used ssh-keygen with no parameters to
 generate the key, and gave it my passphrase when prompted.  I think this is
 all I did for the other box, but I can't remember.  So I don't know if this
 is my problem or something to do with  If you or
 someone else can steer me in the right direction I'd appreciate it.

 James Simmons

 Wade Brainerd wrote:

 On Mon, Feb 2, 2009 at 6:10 PM, James Simmons 

 Second, now that I have this I want to perfect collaboration on my two
 Activities, Read Etexts and View Slides.  Unfortunately, I am convinced
 that collaboration in View Slides that involves sending large Zip
 archives over the network is not and never will be practical.  What I'm
 thinking about now is making the person sharing a slide show see only
 the image being viewed on the XO that has the full presentation.  The
 master XO would page through the slides and those sharing would follow
 along.  I'm not sure that's practical, either.

  I think sending one page at a time, and having the initiator control the
 presentation is a great idea.  Otherwise, you might as well just send the
 document to everyone and have them open it up on their own :)

  Also, are you planning to move your repositories over to  Most of the other activities are doing that now, and
 we have set up a Sugar Labs ActivityTeam ( to coordinate the process.


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Re: multitouch + audio feedback linux dev - XO-2?

2009-01-26 Thread Nate Ridderman
On Mon, Jan 26, 2009 at 7:22 PM, Nirav Patel wrote:

 1) Are there any existing hooks/systems for Linux for multi-touch?
 That's the only proper way you can get a virtual keyboard to work for
 a double-touchscreen clamshell device (the feasibility of which is not
 sold to me because of the power consumption of running a 2nd screen vs
 a keyboard, and mostly mostly mostly the lack of haptic feedback from
 a virtual keyboard).

 Peter Hutterer has been working on Multi-Pointer X for several years.
 It is getting pretty usable, judging by the Youtube videos.

Jim Gettys put together a synopsis of multi-touch input for XO-2 in
September -

2) Audio feedback
 A big problem with touch-screen/virtual keyboards is lack of haptic
 feedback (and haptic feedback would probably eat batteries a lot). A
 standardized/universal audio mapping to keyboard keys similar to
 QWERTY, Dvorak or Braille would help solve this.

I have some insight into this topic from experience in the cell phone
industry. There are several ways to do haptic responses: linear vibrators,
piezo-electric elements, speakers. Localized haptics are best (the vibration
comes from the area on the screen that has been touched), but that's still
an emerging technology. The challenge with your idea is latency. For
applications like typing, the haptic response must happen very quickly to
trick the brain into thinking it is related to the press. I think I've heard
the number 25 ms before, but don't quote me on that. A quick google search
couldn't confirm or deny this. I did find an interesting paper ( that stated
100-200 ms was the limit, but I don't think the results apply to typing. The
game in their experiment took a second to complete, which is way longer than
a keystroke takes. If you don't care about typing repeatedly, the latency is
less important. But for typing quickly with a  limit of 25 ms, it will be
hard to interrupt the processor, load a sound file, and play it in time. A
dedicated microprocessor might be up to the task though.

Also, I'm not sure if a speaker would draw significantly less power than a
piezo or linear vibrator. I don't remember hard numbers for either use case.

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Re: New joyride build 2613

2008-12-30 Thread Nate Ridderman
On Tue, Dec 30, 2008 at 3:51 PM, wrote:

 I thought you were trying to not have perl in the system?

My understanding is that Joyride builds are kicked off automatically when
there is something new to build. A new version of Perl was posted to the
Fedora repositories, so Joyride picked it up. This doesn't mean that perl
will stick around. Please correct me if I misstated something.

On Tue, Dec 30, 2008 at 2:42 PM, Mikus Grinbergs wrote:
 Why not start putting 0.84 in Joyride ?


Sucrose 0.83.x is an unstable development series intended for testing and
development purposes. Sucrose uses odd minor version numbers to indicate
development status, so this unstable 0.83.x series will eventually become
the 0.84 stable release. 

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Re: 9.1 Proposal: Power.

2008-10-23 Thread Nate Ridderman
Do we have the ability to pulse width modulate the backlight LEDs? What is
the resolution on the PWM? It's hard to know if this is feasible without a
hardware schematic and specs on the backlight driver. The CL1 spec mentions
a PWM signal, but maybe it only has four bits of resolution?

In the cell phone world, PWM is used pretty regularly as an approach to dim
backlights. It's much cheaper than having a bunch of analog current sensing
circuitry. I believe 100 Hz or greater is required to reduce flickering, but
this might be higher on a larger screen. Sometimes using PWM on LEDs can
create spectral noise, especially if there is no soft start mechanism in the
LED driver, so the antenna desensitivity would probably need to be tested
against this approach.


On Thu, Oct 23, 2008 at 4:45 PM, Jim Gettys [EMAIL PROTECTED] wrote:

 How well we can do that isn't clear.

 We have 16 brightness levels, but we didn't think about making them
 logarithmic in response to correspond to the eye's behavior, so there
 are really fewer than that that are useful.

 Please experiment and see if it is helpful, of course...
  - Jim

 On Thu, 2008-10-23 at 10:14 -0400, Eben Eliason wrote:
  I could be talking nonsense, and perhaps this would consume more power
  than it saves, but if you were able to slowly dim the backlight over
  the course of a minute or so, instead of waiting a minute and then
  dropping it suddenly, we could prevent the sudden change which causes
  a break in concentration.  (As long as the screen is bright enough to
  be usable when dim, of course.)
  - Eben
  On Wed, Oct 22, 2008 at 4:21 PM, Chris Ball [EMAIL PROTECTED] wrote:
  When running on battery with Energy Saver set to Better Battery
  Life (which sets Automatically reduce the brightness of the
  display before display sleep) the backlight dims after 30 seconds.
  On AC with the equivalent setting it's 2 minutes, 30 seconds.  In
  each case the dimming time seems to be 50% of the time until the
  screen is turned off.  1 minute is the minimum time before display
   Thanks!  I was hoping someone would have numbers.  Our backlight dim
   currently happens fifty seconds after idleness starts, so we're
   definitely less aggressive than OS X already..
   - Chris.
   Chris Ball   [EMAIL PROTECTED]
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Re: Stability and Memory Pressure in 8.2

2008-09-10 Thread Nate Ridderman
My layman's understanding is that you can't execute in place from the NAND
flash on the XO. XIP requires NOR flash which is more expensive than NAND
but has faster read speeds. It mentions this briefly on the axfs FAQ.

Storing some executables and libraries in a separate uncompressed partition
seems more plausible, but I can't speculate on the system performance


On Wed, Sep 10, 2008 at 9:38 AM, [EMAIL PROTECTED] wrote:

 On Wed, 10 Sep 2008, Tomeu Vizoso wrote:

  On Wed, Sep 10, 2008 at 11:53 AM, John Gilmore [EMAIL PROTECTED] wrote:
  It may be possible and useful to store some commonly used executables
  and shared libraries as uncompressed files in jffs2, making them much
  faster to page back in from Flash.  Nobody has tried doing this, as
  far as I know.
  Please, I would love to see this as well...

 not for this release, but would the axfs be an option in the future with
 it's execute in place capability for key files? or is the performance
 difference compared to ram such that you wouldn't want it in any case?

 either way, the profiling it does of which pages are used (and how much)
 could be useful in figuring out what binaries should be stored

 David Lang
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Re: PlayGo Patches/Commit access

2008-07-19 Thread Nate Ridderman

Go is one of my favorite games, so I'm excited to see that someone has
picked up development again! It requires such balance between aggressiveness
and defense, as well as local play vs spreading out on the board - I think
it's a great game for kids to learn. I look forward to trying out a new
version, and I agree that collaboration is an important problem to tackle
soon. Adding GnuGo ( support would be a
great addition too. It would be nice to support GnuGo and collaboration over
the same networking framework, but I don't know enough about the
collaboration framework and Bitfrost to know if this is a possibility. GnuGo
generally runs as it's own process and communicates over GTP (

It seems there's a lack of documentation for people like yourself who want
to pick up development on an existing activity. Most people who want shell
access to also want to host a new activity. I wasn't able to
find anything on the wiki about requesting shell access. Maybe putting a
blurb on the wiki about who to contact would be helpful.


2008/7/19 Andrés Ambrois [EMAIL PROTECTED]:

  Hello all!

  I've recently started learning python and sugar programming and, while
 trying to be useful in the meantime, have been tinkering around with the
 PlayGo activity.
  I have a few patches that add basic scorekeeping, error messages
 (like: There already is a stone there!), and small code cleanup. I'd like
 to start tackling bigger problems (like collaboration) in the future.
 However, cjb told me on #sugar the best way to get this commited is having
 commit access to the git repo. I couldn't find a Commit access
 in the wiki, so I'm using part of the project hosting application here :) :

 1. Project name   : PlayGo
 2. Existing website, if any :
 3. One-line description : A Go game activity

 6. Committer list:
Username   Full name SSH2 key URLE-mail
 #1  aa  Andrés Ambrois

 11. Translation
   [X] Set up the Pootle server to allow translation commits to

 12. Notes/comments: The project already is on the git repository:;a=summary . But I couldn't
 it in the pootle server. It'd be great to have it added.

 Also, I'm Uruguayan so I'll take care of the spanish translation :). If
 needs any help with Spanish, I'm usually around at #olpc :D

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