Light Activated Wireless Burglar Alarm 2
This circuit is actually an AM radio transmitter which is turned on when the necessary amount of light strikes the CdS. You will need an AM radio tuned to a weak station to receive the alarm signal from this project.
When the wiring is complete, you will need to adjust the Control to the desired sensitivity for the switch section of the circuit (the CdS, 50K Control, 10K Resistor and 2SC Transistor).
You will probably want the transmitter to be activated by low light levels. Then if you place the alarm in a dark place (like a desk drawer or closet) it will send a signal to the nearby radio receiver whenever light hits the CdS.
The transmitter section of this circuit consists of two oscillators. One produces the RF (radio frequency) signal and the other produces the audio frequency signal.
The signal from the audio oscillator controls the amplitude (strength) of the RF signal. These changes in RF signal amplitude (controlled by the audio oscillator) are called modulation.
The amplitude modulations are turned into sound by the AM radio. By the way, that's where AM radio gets its name . . . Amplitude Modulation.
Have fun with this circuit, and see whom you can catch!