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Drives one LED array for positive potential, drives other LED array for negative potential. The upper voltage source(s) are representative of the potential at the base of the transistor. I've built a couple circuits now, based on this concept, and with a bare-ended jumper wire, it performs well with a 100 μH inductor at the base of the pick-up PNP.
This is an exercise in teaching myself analog circuit design, and is still a work in progress. Ideally, the green LED would be center gauge, and light first for either side (positive OR negative), with the remaining 3 LEDs driving up or down the scale. I realize there are easier ways to make this circuit; op-amps or some such, but I have loads of transistors on hand, and it's become a matter of principle now.
Any pointers would be welcome, or even a work-around with a 555, since I have some of those too, just haven't ever designed a circuit with one.
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