Cat repeller
Long range IR beam break detector
Driving a 3-phase AC motor
Useless box improvement
Very stable magnetic levitator
Mazzilli (ZVS) oscillator improvement (start-help)
Wireless power transfer
Radio button circuit
Solid-state foot or hand warmer
Audio cable tester (XLR to XLR, XLR to jack (mono/stereo), jack to jack (mono/stereo)
LC oscillator converts to a low voltage LED driver