Cds controlled IC oscillator BA546
This project is a circuit with the IC as an oscillator. The tone of this oscillator varies with the amount of light hitting the CdS cell.
Try changing the tone by moving your hand over the CdS cell. The CdS cell acts as an open circuit in total darkness, but when some light strikes the CdS cell its resistance decreases enough to allow feedback of output signal to get through and sustain oscillations.
You might want to try using different values of resistors to see if there are any changes in oscillation. You can try every capacitor without fear of damage. Have fun!