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Author Topic: Using phototransistors - hardware check.  (Read 2231 times)
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Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
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From the figures you posted at the start, and given that you are supplying the phototransistor from a separate 1.5v supply, I suspect that what you were measuring was not change in light intensity but the reduction in Vcc as you increase the average LED current. Also, 68 to 470 ohm sounds way too low for the series resistor to me. What happens if you repeat the measurement but put something between the LED and phototransistor to block the light?

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