Input Controls
Live Display
| A | B | Output (Y = A + B) |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Current Observation
Set inputs A and B using the toggle switches and observe how the OR gate processes the signals. The output will be HIGH (1) when either or both inputs are HIGH (1).
Signal Flow Observation
Toggle the switches to observe the signal flow animation through the wires. Notice how the output becomes HIGH when any input signal reaches the OR gate as HIGH.
Definition
An OR gate is a fundamental digital logic gate that produces a HIGH (1) output when any of its inputs is HIGH (1). The output is LOW (0) only when all inputs are LOW (0).
Working Principle
The OR gate performs logical addition. It compares the logical states of its inputs and produces an output based on the OR Boolean operation. The gate can be implemented using diodes, transistors, or CMOS technology.
- When either Input A OR Input B is HIGH → current flows through at least one path → output is HIGH.
- When both inputs are LOW → no circuit path is active → output is LOW.
Truth Table Summary
The OR gate has 2 inputs and 4 possible input combinations. Three combinations produce a HIGH output. Only one combination (A=0, B=0) produces a LOW output.
Boolean Expression
Y = A + B (also written as Y = A OR B)
Industrial Applications
- Emergency Alarm Systems: OR gates are used in alarm circuits where activating any one of multiple emergency switches triggers the alarm.
- Fire Detection Systems: Multiple smoke or heat detectors connected through OR logic — if any single detector triggers, the alarm sounds.
- Redundant Safety Systems: Multiple sensors monitoring critical parameters — if any sensor detects a fault, the system initiates a shutdown.
- Digital Electronics: OR gates are building blocks of adders, encoders, multiplexers, and other combinational circuits.
- Intrusion Detection: Multiple entry points (doors, windows, motion sensors) connected through OR logic — breach at any point triggers the security system.
Boolean Expression
Y = A + B
The plus sign (+) represents the OR operation in Boolean algebra. It is equivalent to logical addition for binary values.
Boolean Algebra Properties of OR
- Identity Law: A + 0 = A
- Null Law: A + 1 = 1
- Idempotent Law: A + A = A
- Complement Law: A + A' = 1
- Commutative Law: A + B = B + A
- Associative Law: (A + B) + C = A + (B + C)
- Distributive Law: A + (B · C) = (A + B) · (A + C)
Current Calculation
A = 0, B = 0 → Y = 0 + 0 = 0
Emergency Alarm System
This demonstrates an emergency alarm system. The alarm activates when either emergency switch is pressed. If any switch is ON, the alarm sounds immediately.
This OR gate logic ensures that any single emergency trigger is sufficient to activate the alarm — maximising safety response.