7mm tiny homemade battery
Just glue and Alum. A piece of copper on one side and a piece of galvanized steel on the other. Enough power to run a blocking oscillator circuit 🙂 See Lidmotor’s channel for the circuit..it’s his ‘Penny’ circuit. My coil is from Hartley oscillator experiments, approx 38 gauge wire, 400 turns one way, 200 turns the other on this one. 850K slider, C1815 NPN transistor, 100uF electrolytic, ‘104’ ceramic capacitors.