Parts List: Resistors are 1/4W, carbon, 5% tolerance (or better). R1 = 100K IC1 = 4069 C1 = 0.02 (22nF) LDR1,LDR2 = Light Dependent Resistor C2 = 0.1uF (100nF) T1 = Audio Transformer, 1000:8 C3 = 100uF/16V electrolytic S1 = On/Off switch C4 = 100uF/16V electrolyticNote:
This circuit uses a common CMOS 4069 IC. The MC14069 is pin for pin compatible.
The 4069 has six inverters, but only three are used.
The first two inverters operate as an digital audio oscillator, and the third as an audio transformer low-gain linear audio amplifier.