Light-level-detector

Description: If R, the sensor matching resistor, is equal to the "dark" resistance of the cadmium sulfide cell, the amplifier output will range from 0 to 2 as the light level varies from "dark" to "bright." The circuit operates similarly, but uses the standard non-inverting configuration instead of the voltage-follower configuration; this allows for variable gain. Although the "dark" resistance of the cadmium sulfide cell is only 7 kΩ, the principles of operation apply to other types of detectors that require the high input impedance of the HA-5180 for reasonable linearity and usability.

The described circuit utilizes a cadmium sulfide (CdS) cell as a light-dependent resistor (LDR) to modulate the output of an operational amplifier (op-amp). The sensor matching resistor (R) is strategically chosen to match the "dark" resistance of the CdS cell, which is typically around 7 kΩ. This configuration ensures that the amplifier's output voltage varies linearly in response to changes in light intensity, transitioning from a low output in dark conditions to a higher output in bright conditions, effectively ranging from 0 to 2 volts.

In the standard non-inverting configuration, the op-amp amplifies the voltage across the CdS cell, allowing for variable gain adjustments. This is advantageous for applications where the sensitivity of the light detection needs to be finely tuned. The op-amp employed in this circuit, the HA-5180, is noted for its high input impedance, which is essential for maintaining the linearity of the response and ensuring that the CdS cell operates effectively without loading effects that could distort the signal.

The circuit design can be utilized not only with CdS cells but also with various other types of photodetectors that exhibit similar resistance characteristics. The flexibility of the op-amp configuration allows for adaptation in different sensing applications, making it a versatile choice for light measurement and control systems. By ensuring that the input impedance remains high, the circuit can accommodate a range of sensor types while maintaining accurate and reliable performance across varying light conditions.If R, the sensor matching resistor, is equal to the "dark" resistance of the cadmium sulfide cell, the amplifier output will range from 0 to "" 2 as the lightlevel ranges from "dark" to "bright." The circuit in Fig. B operates similarly, but use the standard noninverting configuration instead of the voltage-follower configuration;

this allows for variable gain. Although the "dark" resistance of the cadmium sulfide cell is only "" 7 KO, the principles of operation apply to other types of detectors which require the high-input impedance of the HA-5180 for reasonable linearity and useability.