Description
The 4-pin LDR (Light-Dependent Resistor) sensor module is a compact light detection board built around a cadmium sulfide (CdS) photoresistor and an LM393 voltage comparator. It provides both digital and analog outputs simultaneously, making it one of the most versatile and beginner-friendly light sensing modules available. The photoresistor’s resistance decreases as incident light intensity increases—typically from several hundred kilohms in darkness to a few kilohms under bright illumination—and the module converts this resistance change into usable electrical signals .
The digital output (DO) switches between HIGH and LOW when ambient light crosses a threshold set by the onboard potentiometer. The analog output (AO) provides a continuous voltage that varies with light intensity, allowing precise measurement of relative brightness through any microcontroller ADC . The module operates from 3.3V to 5V, making it directly compatible with Arduino, ESP32, Raspberry Pi (digital pin only), and most hobbyist platforms. Typical applications include automatic lighting control, light-seeking robots, brightness monitoring, and educational sensor experiments.
Important note: This module provides relative light levels, not calibrated lux measurements. Absolute light intensity requires calibration against a reference instrument.
Features
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Dual Outputs (DO + AO): Digital threshold signal and analog intensity reading available simultaneously .
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Adjustable Sensitivity: Onboard potentiometer sets the digital switching threshold for light/dark detection .
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LM393 Comparator: Provides clean, stable digital switching with good driving capability (15mA) .
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Wide Voltage Compatibility (3.3V–5V): Works with both 3.3V and 5V logic systems .
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CdS Photoresistor Sensing: Peak sensitivity around 540nm (visible light), with fast 30ms response time .
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Power and Output Indicators: Onboard LEDs show power status and digital output state .
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Compact PCB with Mounting Holes: Approx. 33×14mm board with screw holes for easy installation .
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Beginner-Friendly: Simple 4-wire connection and readily available example code for Arduino and other platforms.
Technical Specifications
| Parameter | Specification |
|---|---|
| Sensor Element | CdS Photoresistor (LDR), GL55 series typical |
| Comparator IC | LM393 |
| Operating Voltage | 3.3V – 5V DC |
| Outputs | Digital (DO) + Analog (AO) |
| Light Resistance (10 Lux) | 5–10 kΩ (GL5516 typical) |
| Dark Resistance | 0.5 MΩ (GL5516 typical) |
| Spectral Peak | 540 nm |
| Response Time | ~30 ms rise/fall |
| PCB Size | Approx. 33 × 14 mm |
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