Editing N900 light meter

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The light meter lets the software on the [[Nokia N900|N900]] sense ambient light levels.

==Hardware==

The device is a TAOS [http://www.taosinc.com/downloaddetail.aspx?did=141 TSL2563], now AMS [http://www.ams.com/eng/content/download/250126/975581/TSL2563_Datasheet_EN_v1.pdf TSL2563]

==Software==

It is handled by the kernel module tsl2563.

The kernel driver exposes the [[:wikipedia:lux|lux]] value in the sysfs file
 cat /sys/class/i2c-adapter/i2c-2/2-0029/lux
 21

Under MeeGo it's available as
<pre>
cat /sys/class/i2c-adapter/i2c-2/2-0029/device0/illuminance0_input
</pre>

Under Maemo-Leste it is available as
<pre>
/sys/class/i2c-adapter/i2c-2/2-0029/iio:device1/in_illuminance0_input
</pre>

Note: please check! This might only be one of the two different spectral channels and thus yield vastly incorrect LUX values when massive IR light has impact on the sensor. The lux value of N900 is a derived value from an [http://www.ams.com/eng/content/download/251504/992805/version/3 algorithm] calculating ''visible'' lux from roughly a difference between the two sensor values the ALS provides
 The TSL2562 and TSL2563 are second-generation ambient light sensor devices. Each contains two integrating analog-to-digital converters (ADC) that integrate currents from two photodiodes. Integration of both channels occurs simultaneously. Upon completion of the conversion cycle, the conversion result is transferred to the Channel 0 and Channel 1 data registers, respectively. 
 The transfers are double-buffered to ensure that the integrity of the data is maintained. After the transfer, the device automatically s begins the next integration cycle.
[http://wstaw.org/m/2014/10/20/plasma-desktoprI1874.png diagram of spactral sensitivity channel0/1]

Third party applications that use this sensor include [http://www.tuug.fi/~toni/serendipity/index.php?/archives/14-Luxus-Light-Meter-v0.2-for-N900,-as-a-real-homescreen-widget.html Luxus Light Meter] and [http://norayr.arnet.am/weblog/?p=1710 photographic light meter].

The sensor is also used to modulate the backlight in response to ambient light, although this behaviour [[Disable the ambient light sensor|can be disabled]].

[[Category:N900 Hardware]]

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Editing N900 light meter

@@ Line 26: / Line 26: @@
   The TSL2562 and TSL2563 are second-generation ambient light sensor devices. Each contains two integrating analog-to-digital converters (ADC) that integrate currents from two photodiodes. Integration of both channels occurs simultaneously. Upon completion of the conversion cycle, the conversion result is transferred to the Channel 0 and Channel 1 data registers, respectively.
   The transfers are double-buffered to ensure that the integrity of the data is maintained. After the transfer, the device automatically s begins the next integration cycle.
-[http://wstaw.org/m/2014/10/20/plasma-desktoprI1874.png diagram of spectral sensitivity channel0/1]
+[http://wstaw.org/m/2014/10/20/plasma-desktoprI1874.png diagram of spactral sensitivity channel0/1]
 Third party applications that use this sensor include [http://www.tuug.fi/~toni/serendipity/index.php?/archives/14-Luxus-Light-Meter-v0.2-for-N900,-as-a-real-homescreen-widget.html Luxus Light Meter] and [http://norayr.arnet.am/weblog/?p=1710 photographic light meter].