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 electrolytic

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.

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Copyright © 2006, Tony van Roon