@▷ Light Detector Schematic | Diagram for Schematic

Light Detector Schematic

Light Detector Schematic Diagram 300x263 Light Detector Schematic

Here the simple, low-cost and easy built light detector schematic. The circuit is working with photoresistor to sense the light and timer IC 555 to generate a tone and deliver the tone to the speaker. This circuit detects light falling on the Photo-cell (Light Dependent Resistor) to activate the 555 and generate a tone which is sent towards the speaker. Pin 4 has to be kept less than 0.7v to make the 555 off. Any voltage higher than 0.7v will activate the circuit. The variable sensitivity control is necessary to set the level at which the circuit is activated.

When the sensitivity potensiometer is rotated so that it has the minimum resistance (as shown in red), a large amount of light has to be detected by the LDR for its resistance to be low. This generates a voltage-divider made up of the LDR and 4k7 resistor. Since the resistance of the LDR reduces, the voltage across the 4k7 raises and also the circuit is activated.

When the sensitivity control is obtained to the 0v rail, its resistance raises and this successfully adds resistance to the 4k7. The lowerpart of the voltage-divider now has a greater resistance and this is in series with the LDR. A smaller amount light is required on the LDR for it to increase the voltage on pin 4 to activate the 555.

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