Light sensor on XO-1.75

Bert Freudenberg bert at
Tue Aug 30 09:50:47 EDT 2011

On 30.08.2011, at 01:38, Richard Smith wrote:

> On Mon, Aug 29, 2011 at 1:06 PM, Bert Freudenberg <bert at> wrote:
>> On 17.08.2011, at 17:24, Martin Langhoff wrote:
>>> Saadia Baloch (4):
>>>      Driver to read Outdoor Light Sensor from EC on OLPC.
>> So this is exposed at
>>        /sys/devices/platform/olpc-ols.0/power_state
>> And it seems to sit "behind" the blinking left-most LED? And the blink rate is proportional to the light sensed? Why?
> Its proportional because that's how  the sensor works.  The amount of
> light changes the time to bleed off the charge stored in the diode
> when you reverse bias it.

Ah, so you use the LED itself to sense light? And then time how long a cycle takes in the EC? Awesome design!

This almost takes the cake over the analog mic hack.

- Bert -

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