Mar 272023

Light sensitive sound generator

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

How the Light sensitive sound generator circuit works?

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

The LDR (Light dependent resistor) can be of any type, but it must have a resistance that is between 500 ohms and 5 megohms in normal working conditions. This will allow us to change 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. This cause the sound of the speaker to change in the same way.

Light Sensitive Sound Generator

This circuit gives us a sound with a frequency that depends on the level of illumination that the LDR has. The greater the illumination on the LDR, the higher the frequency of the sound in the speaker will be.

LDR (Light Dependent Resistor)

LDR (Light dependent resistor)

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

741 Op-Amp Pin Configuration and Function

741 Operational Amplifier

List of components for the light-sensitive sound generator circuit

  • 1 741 operational amplifier (IC1)
  • 1 cadmium sulfide LDR, (resistance between 500 ohms and 5 mega ohms). (R1)
  • 2 100K resistors (R2, R3)
  • 1 100 ohm resistor (R4)
  • 1 0.01 uF (microfarads) capacitor (C1)
  • 1 100 uF (microfarads) 18 V or more, electrolytic capacitor (C2)
  • 1 8 to 25 ohms speaker
  • 2 9V batteries

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