Jan 302017
 

Light sensitive sound generator

An oscillator circuit can have many applications. The diagram below shows how to make it work as a light sensitive sound generator using a LDR and a 741 operactional amplifier.

To achieve this we place a cadmium sulfide LDR between the pin 2 and the pin 6 of the operational amplifier 741.

The LDR can be of any type with a resistance that is between 500 ohms and 5 megohms in normal working conditions, which will allow to vary the work frequency in a ratio of 10,000 to 1.

The variation of the LDR resistance, due to the change in light intensity, causes the frequency of the relaxation oscillator to change, causing the sound of the speaker to change in the same way. This gives a sound with a frequency that depends on the level of illumination that the LDR has. The greater the illumination in the LDR, the greater the frequency of the sound in the speaker.

The circuit is powered by two 9V batteries or a dual polarity voltage source (+ 9V/-9V)

Light sensitive sound generator

List of components of the oscillator or light-sensitive sound generator circuit

  • 1  operational amplifier 741 (U1)
  • 1  cadmium sulfide LDR with resistance between 500 ohms and 5 mega ohms. (R1)
  • 2  resistors of 100K (R2, R3)
  • 1  100 ohm resistor (R4)
  • 1  capacitor of 0.01 uF (microfarads) (C1)
  • 1  electrolytic capacitor of 100 microfarads, 18 V or more (C2)
  • 1  8 to 25 ohms speaker
  • 2  9V batteries
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