Subject:
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Re: Shutting off illumination LED on Light Sensor for LIDAR
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 1 Apr 2001 19:50:50 GMT
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Viewed:
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883 times
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jetleb@netcom.ca (Matthias Jetleb) writes:
>
> > Someone else mentioned that LegOS is able to read the light
> > sensor 'passively' without illuminating the LED. Any LegOS
> > folks here know what they do differently?
>
> I strongly suspect this is a myth. A transistor is a transistor is a
> transistor. They all require biasing in order to function properly and
> that requires power. Mind you, even so-called passive devices must
> either generate a voltage or have a voltage present in order to read
> their value, and it's probably that reduced voltage that is in fact
> powering the light sensors. Not a high enough voltage to light the LED
> (min 1.2V - more likely 1.9V - I haven't tried it yet) but enough to
> get the photo-transistor biased (but not properly), Hence a weak and
> non-linear reading.
Actually you don't need LegOS, any input set to raw mode
with the LEGO firmware will do fine.
This is because even in passive mode there is a pull up of 10k to 5V,
and in fact the LED is glowing dimly in this mode.
Just tried it, I can get raw values from ca 530 (dark)
down to ca 380 (at not-quite-frying distance to a halogene light).
Jürgen
--
Jürgen Stuber <stuber@loria.fr>
http://www.loria.fr/~stuber/
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