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I have a small 1.5 volt useless solar panel. Is it possible to have the resistance change between two wires based on the amount of light? And what would the circuit look like?

placeholder
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skyler
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  • define LDR to make your question clearer – placeholder Mar 24 '13 at 21:02
  • Light Dependent Resistor – skyler Mar 24 '13 at 21:02
  • If you could explain what you are trying to achieve it could be that Olin's answer is the most practical. On the other hand if you insist that you wanted resistance variation with light on the panel then a different circuit may be appropriate. Focus on what you want this "thing" to do rather than thinking "maybe this is what I need to add to something else to achieve function or performance X" – Andy aka Mar 24 '13 at 21:12
  • So lets say I wanted a circuit that drove an LED and when there was no light, the LED turns on and when there is light, the LED turns off, would a single transistor inverter work? – skyler Mar 24 '13 at 21:47
  • It's not a resistor, more like a giant photo diode. – starblue Mar 25 '13 at 09:14

2 Answers2

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It's not the resistance that varies much with light, so no, I wouldn't use the panel that way.

However, the short circuit current is pretty linear with light, so you could make a circuit that detected light that way. One way to do this is to use a opamp in transimpedance configuration. It turns a current into a voltage while keeping the input voltage nearly fixed.

Olin Lathrop
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  • So lets say I wanted a circuit that drove an LED and when there was no light, the LED turns on and when there is light, the LED turns off, would a single transistor inverter work? – skyler Mar 24 '13 at 21:47
  • @skyler: You could possibly do this with a transistor, resistor, and LED, but you would need some external power source. However, that has little to do with what you asked. – Olin Lathrop Mar 24 '13 at 22:59
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    okay I think i should"ve thought through this more before I asked it. – skyler Mar 24 '13 at 23:36
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Yes, but not directly. solar cell could be modeled as a current source relative to the light intensity. You could simply use a current mirror with 100:1 ratio and convert that current into variable resistance.Where FET could be used as a voltage varies resistance(using the early effect). BTW, it could be only applicable to small signal analysis.

Standard Sandun
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