Re: Longer XO transformer power cord in the plans?

2009-05-31 Thread Reinder de Haan


Sascha Silbe wrote:
 On Sun, May 31, 2009 at 03:16:53PM +1000, James Cameron wrote:
 
 1.  Earthing.  The current design has no earth at the AC end, and is
 isolated in relation to the DC end.  An earthed AC plug in some
 countries produces a more reliable and positive insertion and anchoring.
 All travel adapters (power outlet adapters) I've come across so far
 had no earthing so would be impossible to use (unaltered). Of course
 this wouldn't be much of a change as the current wall warts also don't
 fit any adapter I've seen at shops. At SugarCamp in Paris, quite a few
 people (including myself) had custom ones, i.e. with mechanic
 alterations.
 Personally, I feel comfortable making minor mechanic changes to an
 adapter, but I won't usually dare using a non-earthing adapter with a
 device having an earthed plug (unless I know for sure this is safe).
 
 Actually, if you are able to use a standard plug (e.g. IEC-60320-C5/C6)
 at the power supply end, above won't apply at all as it's usually easy
 to get a matching cable, no travel adapter needed. :)

+1 for inline adaptor its MUCH easier to exchange only the mains cable:
1) when its demaged
2) when shiping to a different part of the world
 you would need only one powersupply brick for (almost?) all or the world.
i have seen some companies ship a couple of different cables so the
device is usable almost everywhere and doesn't need to be custom
packed/country.

i would go which IEC-60320 C8/C9 which is used for half of the laptops
today.

i feel a earthed design only increases the risks, even more so when you
cant depend on the quality of the mains supply.
the only advantage to the earthed design that im aware of is that the
power supply easier(cheaper?) meets EMC/FCC regulations.

 
 I hope future XO versions will still have the same broad power input
 specs as the XO-1. It's been very useful already (e.g. cable-only car
 adapter, no voltage conversion or even voltage limit necessary).
 
 CU Sascha
 
 
 
 
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Re: Longer XO transformer power cord in the plans?

2009-05-31 Thread Reinder de Haan

Tiago Marques wrote:
 On 5/31/09, Reinder de Haan r...@mveas.com wrote:

 Sascha Silbe wrote:
 On Sun, May 31, 2009 at 03:16:53PM +1000, James Cameron wrote:

 1.  Earthing.  The current design has no earth at the AC end, and is
 isolated in relation to the DC end.  An earthed AC plug in some
 countries produces a more reliable and positive insertion and anchoring.
 All travel adapters (power outlet adapters) I've come across so far
 had no earthing so would be impossible to use (unaltered). Of course
 this wouldn't be much of a change as the current wall warts also don't
 fit any adapter I've seen at shops. At SugarCamp in Paris, quite a few
 people (including myself) had custom ones, i.e. with mechanic
 alterations.
 Personally, I feel comfortable making minor mechanic changes to an
 adapter, but I won't usually dare using a non-earthing adapter with a
 device having an earthed plug (unless I know for sure this is safe).

 Actually, if you are able to use a standard plug (e.g. IEC-60320-C5/C6)
 at the power supply end, above won't apply at all as it's usually easy
 to get a matching cable, no travel adapter needed. :)
 +1 for inline adaptor its MUCH easier to exchange only the mains cable:
 1) when its demaged
 2) when shiping to a different part of the world
  you would need only one powersupply brick for (almost?) all or the world.
 i have seen some companies ship a couple of different cables so the
 device is usable almost everywhere and doesn't need to be custom
 packed/country.

 i would go which IEC-60320 C8/C9 which is used for half of the laptops
 today.
 
 Completely not the picture around this part of Europe. Most of them
 come with C13 and some are being sold with C7, which is pretty much a

oops i meant C7/C8 NOT C9!!

 standard for other types electronics. C13 would be my favorite, if the
 size of the plug is not an issue, since it is also the standard for
 computer power supplies. As mentioned above, C5 would also be sweet.

both are an earthed connector and so 'require' an earthed outlet.
combined with that almost all power supplies i have seen with a C5/C6 or
C13/C14 connect the earth input to the ground/0V dc output...
if you insert such power supply into an not earthed outlet (which are
quite common)
your whole laptop will be at ~1/2*Uin Vac due to the filter capacitors
in the mains filter.
which gives a nasty shock if you touch both a non insulated part of your
laptop and a earthed object..


 As for safety, adding something like the cable plug of the original
 Xbox pads would work perfectly and it's not as expensive as Apple's
 magnetic plug. Cost of this is something I have no clue about.
 
 Best regards,
 
 Tiago Marques
 
 i feel a earthed design only increases the risks, even more so when you
 cant depend on the quality of the mains supply.
 the only advantage to the earthed design that im aware of is that the
 power supply easier(cheaper?) meets EMC/FCC regulations.

 I hope future XO versions will still have the same broad power input
 specs as the XO-1. It's been very useful already (e.g. cable-only car
 adapter, no voltage conversion or even voltage limit necessary).

 CU Sascha


 

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Re: [Fwd: Re: Ambient light sensing via LED response]

2009-05-10 Thread Reinder de Haan


C. Scott Ananian wrote:
 On Wed, May 6, 2009 at 6:14 PM, Reinder de Haan r...@mveas.com wrote:
 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.
 
 I think the actual A/D reference voltage is probably *maximum* 3.3V.
 What's the *minimum* A/D reference voltage?  And can the A/D measure
 all the way down to ground?  (Sometimes there's a Vmin for the A/D
 input, often around a diode drop above ground.)
 
 i did some more experiments and at ~20 cm from the halogen lamp i doest
 matter is i turn the backlight full on of off .. i dont have color
 anymore
 at that distance the bare led gave about 250mv (maybe a bit more into a
 very high R fet gate...)


that 250mv is without the light guide and lcd cover installed!
with the light guide in place its more like ~70mv ...
0.07/3.3*256= 5.4 LSB and then the Rin of the ADC must be 10Mohm...

 
 250mv should be a count of about 20 from the A/D.  That's plenty for
 this purpose.  Heck, a count of 1 would be sufficient, as long as it
 was repeatable. ;-)
 
 So, it seems like all that's required is one wire from the top of the
 LED to the A/D input, and wiring Vref directly to +3.3.  Adding a
 zener and a resistor for a lower Vref would probably improve precision
 and accuracy.
 
 Everything else is software  tweaking some constants.
   --scott
 

if i find the time somewhere this week i might test it ... otherwise it
will be during of after paris..

Reinder
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[Fwd: Re: Ambient light sensing via LED response]

2009-05-06 Thread Reinder de Haan


 Original Message 
Subject: Re: Ambient light sensing via LED response
Date: Thu, 07 May 2009 00:02:49 +0200
From: Reinder de Haan r...@mveas.com
To: raf...@laptop.org
References: 200904290017.n3t0hl2v006...@new.toad.com
c5d4a4e5-b183-4b7d-bafb-3488e15f7...@laptop.org
c6d9bea0905011128j2d5cdf3cw975cfad790480...@mail.gmail.com
675d3c5c-95ed-4ee9-84bc-3b5164675...@laptop.org
c6d9bea0905042207i458ed9b1if74e0e16d24f5...@mail.gmail.com
4a00a073.8020...@mveas.com
a80d16920905051544s525b7039nf7e87a4a3c754...@mail.gmail.com
75dc0458-925b-4792-9aee-a24b9b1f3...@laptop.org
a80d16920905051952h3d82d15brb8f690cf1c402...@mail.gmail.com



Rafael Enrique Ortiz Guerrero wrote:
  
 
 
 On Tue, May 5, 2009 at 8:34 PM, John Watlington w...@laptop.org
 mailto:w...@laptop.org wrote:
 
 
 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.
 
 
 i don't know if the measurements at sunlight would show the same
 variations.. we would have to make new measurements, but for experience,
 the variations of voltage regarding light sensing are not of
 considerable amounts, so if the accuracy is 26mv, we would have to see
 if a perceptible change in ambient light could be of a higher magnitude
 than 26mv, if not the accuracy could be lost..
 
 

i did some more experiments and at ~20 cm from the halogen lamp i doest
matter is i turn the backlight full on of off .. i dont have color
anymore
at that distance the bare led gave about 250mv (maybe a bit more into a
very high R fet gate...)

i guess it would be around 70mv whit the light guide in front of it..
(i guess this be more (150mv?) with a very high R (~25 Mohm?) fet gate
as only load)

i would add a simple amp (mosfet? or maybe cheap opamp ?)
to amplify ~X10 so 300mv would be full scale..
my memory is dusty but that should be posible with 2 resistors an a fet
? gain would be posible to change by replacing one of the resistors with
a bigger / lower value...

maybe a trasistor is better bc the leds is acts as a current source ?

ideas welcome

if i can get the partnr of a fet/transistor that would be usable (and
cheap enough) i could maybe order a couple of them from say farnell and
hack something together here

is there a free or hackable input on the current EC ? (or is that
different from the ec that will be in 1.5 ?


 (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...
 
 Ok, thanks :).
  
 
 
 
 
 On Tue, May 5, 2009 at 3:24 PM, Reinder de Haan r...@mveas.com
 mailto:r...@mveas.com 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

Re: Ambient light sensing via LED response

2009-05-05 Thread Reinder de Haan
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








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