Subject:
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Re: LEGO light sensor schematic
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 3 May 1999 14:16:48 GMT
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Original-From:
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rajackson@^antispam^qnx.com
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Viewed:
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1072 times
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Previously, you (Michael Gasperi) wrote:
> > > I was kinda hopeing some bright guys like you would figure out what was
> wrong with it for me so I wouldn't have to.
>
> Well I couldn't wait. I broke down and broke into my Light sensor. All I can
> say is don't do it! The guy that figured out how to package this thing must
> wear a straight jacket. You will break things getting it open.
>
> Other than the already talked about upside down diodes, I found 2 pin numbers
> on the Opamp were switched and that was it. I think it is all correct now. I
> fixed up the circuit and added some measured voltages to make things clearer.
> There is a little analysis added below the circuit for how I think it works.
Ah... much better, I figured one or two components were backwards.
Just to clean up the schematic a bit you could flip R1 (75R) to the right
side of the Q4. I would also bring R8 (12R) in line with the LED.
This would then be a more standard drawing of a current source.
Is the detector a photo diode or a photo transistor? The transistor
Q17 is fuzzy to me as well ;-) I need to think about it some more...
The transistor Q15 looks to be setup to compensate for the drop between
the collector and emiter of Q14. This would improve the linearity of
the output.
>
> I'd forgive this much complexity if it actually worked better, but I'm not all
> that impressed with it. It never goes down much below 20 and who cares how
> linear it is.
>
> http://www.plazaearth.com/usr/gasperi/light.htm
> --
> Did you check the web site first?: http://www.crynwr.com/lego-robotics
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: LEGO light sensor schematic
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| (...) OK, I fixed that and in the process discovered they should be PNPs. 3Hp83 is a BC857 GP PNP from Philips. Looks better now. (...) I think photo diode used in photovoltaic mode. It looks like it pushes the voltage down from that established by (...) (26 years ago, 3-May-99, to lugnet.robotics)
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