LM393: Dual Comparator Explained

The LM393 is a dual voltage comparator that is widely used in sensor circuits, voltage monitoring, signal processing, and microcontroller-based applications. It allows you to compare two voltages and output a digital HIGH or LOW signal based on the comparison.

🔹 1. What is LM393?

• LM393 is a dual comparator, meaning it has two independent voltage comparators inside a single package.
• Unlike an operational amplifier (Op-Amp), it is designed specifically for fast voltage comparison.
• Outputs either HIGH (logic 1) or LOW (logic 0), making it ideal for microcontroller interfacing.

📌 Key Features:

• Dual comparators in one package (can compare two separate voltage pairs).
• Open-collector output (allows interfacing with different voltage levels).
• Low power consumption.
• Can operate from a single power supply (2V – 36V).
• Fast response time (~1.3µs switching speed).

📌 Common Applications:

• Zero-crossing detection (detects when a signal crosses 0V).
• Overvoltage and undervoltage protection.
• Analog-to-digital conversion (ADC) circuits.
• IR sensors, motion detectors.
• Battery level monitoring.

🔹 2. LM393 Pinout & Functions

The LM393 comes in an 8-pin DIP/SOIC package.

📌 How it works:

• Each comparator compares two voltages (IN+ and IN-).
• If IN+ > IN-, the output is LOW (0V).
• If IN- > IN+, the output is HIGH (open-collector, needs a pull-up resistor).

🔹 3. How LM393 Works

• The LM393 outputs a digital HIGH or LOW based on the voltage difference between IN+ and IN-.
• Unlike Op-Amps, the output is open-collector, meaning it requires a pull-up resistor to function properly.

📌 Logic Table for LM393 Comparator:

🔹 4. Using LM393 for a Sensor Circuit

🛠 Required Components

• 1x LM393 Comparator
• 1x LDR (Light Dependent Resistor)
• 1x 10kΩ Resistor (Pull-down)
• 1x 100kΩ Resistor (Reference Divider)
• 1x LED + 330Ω Resistor (Output Indicator)
• 1x 5V Power Supply
• Jumper Wires

🛠 Wiring

📌 How it works:

• When LDR detects bright light, IN+ voltage increases above IN-, and the output goes LOW (LED OFF).
• When LDR detects darkness, IN+ drops below IN-, and the output goes HIGH (LED ON).

🔹 5. Arduino Code for LM393 (Reading Output)

This code reads the output of LM393 and prints the light level.

#define SENSOR_PIN 7  // LM393 output connected to Arduino D7

void setup() {
    pinMode(SENSOR_PIN, INPUT);
    Serial.begin(9600);
}

void loop() {
    int state = digitalRead(SENSOR_PIN);
    if (state == LOW) {
        Serial.println("Bright Light Detected");
    } else {
        Serial.println("Darkness Detected");
    }
    delay(500);
}

📌 What happens?

• When it’s bright, the output is LOW (0V) → The Arduino detects “Bright Light Detected”.
• When it’s dark, the output is HIGH → The Arduino detects “Darkness Detected”.

🔹 6. LM393 for Battery Level Monitoring

📌 Can be used to monitor battery voltage and trigger alerts when voltage drops below a threshold.

✅ Example: Low Battery Indicator

📌 If battery voltage drops below threshold, LM393 output goes HIGH, triggering an alert.

🔹 7. Applications of LM393

✅ Light Sensing (LDR Circuits) – Used for automatic street lights.
✅ Zero-Crossing Detection – Detects when AC voltage crosses 0V.
✅ Overvoltage/Undervoltage Protection – Prevents damage to circuits.
✅ DC Motor Speed Monitoring – Used in tachometers.
✅ Touchless IR Sensors – Common in motion detection systems.

🔹 8. LM393 vs Other Comparators

📌 Verdict:

• LM393 is ideal for digital-level voltage comparisons (requires pull-up resistor).
• LM358 is an Op-Amp, better for analog signal amplification.
• LM339 is a quad comparator (similar to LM393 but with four comparators).

🎯 Conclusion

• LM393 is a dual voltage comparator with an open-collector output.
• Used in light sensing, battery monitoring, zero-crossing detection, and voltage protection.
• Requires a pull-up resistor for output.
• Ideal for microcontroller-based applications (low power, fast switching).