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The Insanity Alarm
The insanity alarm was the first assignment given to our class by our cool teacher, Mr. Dolloff. I assembled the insanity alarm and soldered it together. The alarm is light dependent, which means that when deprived of light, the alarm goes off. Read further for the technical stuff.
Theory of Operation
The C6240 Insanity Alarm Kit consists of a two transistor, direct coupled, oscillator which drives a small piezoelctric speaker. This oscillator is configured to provide a high pitched tone as long as the base of Q2 is biased positve (+). A CDS (cadmium sulfide) cell is placed between the base of Q2 and the emitter of Q2. With the light striking the surface of the CDS cell, its resistance is low enough to change the bias on the base lead to negative (-). With a negative bias on the Q2 base, the oscillator quits working and the kit becomes silent. As soon as the CDS cell is in darkness, its' resistance goes high causing the base of Q@ to be biased positive (+) which turns the oscillator on again.
Parts List
C1,C2..........0018 mF Disc Capacitor
R1.............51K resistor
R2, R3.........1.5 K resistor
R4.............470K resistor
Q1,Q2..........2N3904 transistor
SPK............Piezoelectric speaker
misc...........CDS cell (photocell),9V snap, PC board
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