Joule Thief: JTBasic meets Loopstick Variable Inductor
I took a loopstick variable inductor and wound a “primary” of about 30 turn of #22 on the outside of its windings and potted it in epoxy. A very interesting thing occurred: the test bed does not work with the 70 nF cap switched out. Using only the 1K base resistor, it does not light my series-parallel bank of 24 white LEDs, but with the cap switched in across the base resistor… it lights them brilliantly and enduringly. Not only that but (not shown here) several times I’ve noticed the LEDs getting dim, so I simply and quickly switch the cap switch to “out” and then back “in”….and the brilliance is restored. I don’t understand this. The loopstick wired one way does not respond to moving the ferrite core seemingly at all, but with the coils reversed, it responds strongly to moving the ferrite. Also not understood. Power was a single AA that was discharged and showing 1.2 V no-load.