GSAS Light Dependent Resistor Interface

The LDR interface detects light intensity by converting resistance variation into a voltage, which is compared with a reference using an LM339 comparator. Based on the comparison, a transistor drives a relay to automatically control loads like lamps.

Light sensing is one of the most intuitive and engaging sensor interfacing experiments in embedded systems education. Students can immediately observe the relationship between physical input (covering or illuminating the LDR) and digital output (ADC readings displayed on the trainer), making abstract concepts like analog-to-digital conversion, sensor characterization, and closed-loop control tangible and interactive. The IF-LDR module includes test points for oscilloscope probing, allowing students to observe the raw sensor signal, the conditioned output voltage, and the ADC conversion result at each stage of the signal chain.

The module is compatible with the GSAS 8085, 8086, and 8051 trainer series, connecting through the standard bus connector. Combined with other GSAS I/O modules, such as the relay output module for lamp control or the display modules for measurement readout, the LDR interface enables complete closed-loop control system experiments: measure light level, compare against a threshold, and actuate a lamp or motor to maintain a target illumination level. These multi-module experiments demonstrate real-world embedded control system design within the structured lab environment.

Specifications

Parameter	Value
Sensor	Light Dependent Resistor (photoresistor)
Signal Conditioning	Voltage divider + amplifier circuit
Output	Analog voltage proportional to light intensity
ADC Interface	Compatible with trainer ADC input channels
Test Points	Labelled for oscilloscope probing
Bus Interface	Standard GSAS trainer bus connector
Power	Supplied from trainer kit
Part Number	IF-LDR

Lab Experiment Coverage

Experiment Category	Topics
Sensor Characterization	LDR resistance vs. light intensity, nonlinearity analysis
ADC Interfacing	Analog voltage reading, resolution, sampling rate
Signal Conditioning	Voltage divider design, amplification, filtering
Threshold Detection	Light/dark detection, comparator-based switching
Closed-Loop Control	Light level regulation using LDR + relay/lamp feedback
Data Logging	Continuous light measurement, time-series recording

Compatibility

The IF-LDR module connects to all current GSAS microprocessor trainer kits through the standard expansion bus connector:

• GSAS 8085 Trainer Kit
• GSAS 8086/8088 Trainer Kit
• GSAS 51E Microcontroller Trainer
• GSAS MCB 51 USB Microcontroller Trainer

No additional wiring or external power supplies are required, the module draws power and bus signals directly from the trainer.

Why GSAS

GSAS manufactures the LDR Interface Module in Bangalore as part of its range of sensor and I/O peripheral modules. The LDR is an ideal introductory sensor for embedded systems labs, it is inexpensive, durable, and produces immediately observable results that help students build confidence with analog interfacing before progressing to more complex sensors. The GSAS education products team provides lab manual content for LDR interfacing experiments aligned with Indian university embedded systems curricula.

Products are available for immediate purchase through the GSAS online store (“Buy on Store”) or through direct engagement for institutional and volume orders (“Request Volume Pricing”).