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(...) 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 (...) (26 years ago, 3-May-99, to lugnet.robotics)
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| | 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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| | Re: LEGO light sensor schematic
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(...) [snip] I'm happy to see that some of my concerns have been born out with these changes, it looks more like a happy little circuit now. (...) Are we sure that the photodiode is located in the schematic correctly? It doesn't look like its biased (...) (26 years ago, 3-May-99, to lugnet.robotics)
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| | Re: LEGO light sensor schematic
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Dennis Clark wrote in message ... (...) Your right. It just can't be the way it is drawn. I think it must be a photo transistor. Usually photo diodes are not as sensitive as photo transistors either. I'll touch up the circuit and see if it looks (...) (26 years ago, 4-May-99, to lugnet.robotics)
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| | Re: LEGO light sensor schematic
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Well if anybody still cares, I think the LEGO light sensor circuit is 100% correct now. The sensor is a phototransistor. Looking at the circuit implies a interesting side effect. If you shine a very bright light (ie laser pointer) into the (...) (26 years ago, 4-May-99, to lugnet.robotics)
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| | Re: LEGO light sensor schematic
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(...) Mike, Could it be that transistor 15 (I think), the one that is configured as a diode whose emitter is tied to the emitter on the output of the OpAmp potentially be some kind of non-linear negative feedback loop? Maybe to prevent oscillation (...) (26 years ago, 5-May-99, to lugnet.robotics)
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| | Re: LEGO light sensor schematic
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(...) Transistor 15 only has about .4V across it, so it is not operating in a very linear region. My best guess is that it helps make up for the drop in the follower 14 and provides some nonlinear gain. It tends to lower the gain for larger signals (...) (26 years ago, 5-May-99, to lugnet.robotics)
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| | Re: LEGO light sensor schematic
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Michael, Is your light sensor still in pieces? I was wondering if you could find a moulded Lego part number for the upper half of the brick. -John Van Michael Gasperi <gasperi@alynk.com> wrote in message news:FB614n.JBF@lugnet.com... (...) (26 years ago, 6-May-99, to lugnet.robotics)
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| | Re: LEGO light sensor schematic
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(...) Sorry about that, I glued it back together with liquid plastic cement. I don't think it can take another operation and survive. I can't remember seeing a number inside and I was looking in there when you wedge the pc board in place. You might (...) (26 years ago, 6-May-99, to lugnet.robotics)
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