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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Mon, 2 Apr 2001 16:12:04 GMT
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Original-From:
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Chris 'Xenon' Hanson <xenon@3dnature.comSAYNOTOSPAM>
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Reply-To:
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xenon@3dnature.*ihatespam*com
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Viewed:
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840 times
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Juergen Stuber wrote:
> 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).
Yes, this is the result I discovered this weekend.
My conclusion is that setting the sensor to raw mode does
not fully remove the light produced by the LED, and detrimentally
impacts the sensor performance.
I think my next approach is to try to crack open the light sensor,
and install an externally-accesible jumper to open the circuit across
the LED's leads, so I can enable or disable it at will.
Any suggestions for opening the light sensor without using saws and
hammers?
> Jürgen
Chris - Xenon
--
Chris Hanson | Xenon@3DNature.com | I've got friends in low latitudes!
New WCS 5 Demo Version! http://www.3DNature.com/demo/
"There is no Truth. There is only Perception. To Perceive is to Exist." - Xen
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