Considering building a voltage detector using an LED as an indicator. Of course, if I use it to test 120 VAC then I need a fairly large resistor. But that would eliminate using it to test for 12 VAC, unless I make a selectable range detector. But then I run the risk of setting it for 12 VAC and what happens to the LED if I touch it to 120 VAC?! Keep in mind I'm not only considering just these two voltages I want to use a single LED and a single circuit to detect AC voltages from - oh, lets say 5 volts on up.
I recently read an article about current mirrors. Would that work? I mean set up a current that is correct for the LED then on the mirrored side, regardless of the voltage, the LED won't see more than its required current. Then, conceivably, I could ground one lead and with the other, poke it at a transformer or other device and detect whether there's live voltage there or not. It wouldn't be used to determine the voltage, just to indicate a live line.
Would this work?
I recently read an article about current mirrors. Would that work? I mean set up a current that is correct for the LED then on the mirrored side, regardless of the voltage, the LED won't see more than its required current. Then, conceivably, I could ground one lead and with the other, poke it at a transformer or other device and detect whether there's live voltage there or not. It wouldn't be used to determine the voltage, just to indicate a live line.
Would this work?