Sound Activated Joule Thief
Sound can be used to activate a Joule Thief. A simple 2
transistor preamplifier with a PNP transistor used to switch on
a mosfet Joule Thief circuit. Loud sounds flashes the white led.
Idle current is 300 microamps. Bypass capacitor for the microphone is
important to prevent feedback when the led comes on.
The cube in the center is a vintage Sprague 11Z3201 pulse tranformer
with a 2:1 ratio.
of the prototype here.
PDF of the schematic here.