The light sensor circuit is a sensor-based circuit that detects the presence of light and turns on the LED accordingly. The circuit here uses a LED Flasher IC LM3909. IC LM38909 itself is a low-power flasher circuit, therefore, no external parts areas such as required for the light detection circuit except for an LDR and a capacitor.
Hardware Components
The following components are required to make Light Sensor Circuit
LM3909 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of LM3909
Light Sensor Circuit
Working Explanation
Since the IC LM3909 is a flasher IC hence, the circuit doesn’t require any external electronic components. Hence, the circuit includes an LED, an LDR, a 100µF capacitor, and a battery power source. When light falls on the LDR, its resistance increases. An increase in resistance makes the IC LM3909 Input PIN HIGH. Therefore, the flasher IC does its work and outputs a HIGH signal to light the LED connected to it. Moreover, the capacitor of 100µF, in the circuit, boosts the voltage pulses to 2 or more volts.
Application
- The circuit works as a flashlight in the dark
- Emergency locator
- Circuit inserted in toys
