74LS32 (7432) Logic Gate - Specifications, Pinout, and Application

The 74LS32 (7432) is a TTL integrated circuit that houses four two-input OR logic gates. It is typically powered with +5V (4.75–5.25V), and each gate performs the Boolean operation Y = A+B: the output is "1" if any of the inputs is "1". Only when both inputs are "0" is the output "0".

This component from the 74LS (Low-power Schottky) series is known for its ease of use in breadboards and digital projects involving Arduino, microcontrollers, and telecommunication systems where combined OR logic functions are needed.

What is the 74LS32?

The 74LS32 is a quad low-power OR gate (LS series). Its main features include:

Four independent two-input OR gates.
Low power consumption.
High switching speed (~22 MHz).
Ability to sink up to ~8 mA on a low output.
Compatible with standard TTL levels (5V).

This allows it, for example, to drive LEDs or simple loads directly from the output, making it ideal for basic digital electronics projects.

Basic Operation and Truth Table

Each OR gate inside the 74LS32 operates with a simple logic: the output is "1" when at least one of the inputs is "1". This Boolean operation is expressed as Y = A+B.

Truth table for each OR gate:

Input A	Input B	Output Y
0	0	0
0	1	1
1	0	1
1	1	1

Internal operation: Each gate is based on low-power Schottky TTL technology, using bipolar transistors and Schottky diodes to switch quickly with a typical delay of ~14 ns.

Pinout and Connections

The 74LS32 comes in a 14-pin DIP package with the following configuration:

Pin 7: GND (ground)
Pin 14: VCC (+5V)
Gates organized as follows:
- Gate 1: inputs A (pin 1), B (pin 2), output Y (pin 3)
- Gate 2: inputs A (pin 4), B (pin 5), output Y (pin 6)
- Gate 3: inputs A (pin 9), B (pin 10), output Y (pin 8)
- Gate 4: inputs A (pin 12), B (pin 13), output Y (pin 11)

Note: The pin diagram is identical to that of the 74LS08 (AND) gate, making them easy to swap in prototypes.

Detailed Technical Specifications

Specification	Parameter (74LS32)
Logic Function	OR
Number of OR gates	4 (quad)
Inputs per gate	2
Supply Voltage	4.75 – 5.25 V
Technology	TTL 74LS family (LS-TTL)
Output Current (I_OL)	up to 8 mA (low level)
Output Current (I_OH)	–0.4 mA (high level)
Max. Speed (f_max)	~22 MHz
Typical Delay (t_pd)	~14 ns (propagation)
Operating T_range	0 °C to 70 °C

Key Features:

Standard TTL outputs: Can drive TTL loads and some CMOS components.
TTL-LS Technology: Offers good noise immunity and compatibility with 5V systems.
Four independent gates: Allows for multiple simultaneous OR operations in a single chip.

Component Variants

In addition to the 74LS32 (TTL LS), there are variants compatible with different technologies:

SN7432/SN74LS32: Original TTL versions for 5V.
SN74HC32: High-performance CMOS, operates from 2V to 6V with lower consumption and more powerful outputs (up to 5.2 mA).
SN74HCT32: CMOS with TTL-compatible inputs, ideal for interfacing between 3.3V and 5V logic.
Other variants: 74F32 (Very High-Speed), 74S32 (High-speed Schottky).

Practical Applications

Use cases with Arduino and microcontrollers

The 74LS32 is very useful in digital prototypes where signals need to be combined:

Arduino UNO (5V): Can be used to activate an output if any of several conditions are met (e.g., sensor A or sensor B is triggered).
3.3V Microcontrollers (ESP32, etc.): It is more appropriate to use the 74HC32/HCT32 version for logic level compatibility.
Alarm systems: Activating a siren if a door or a window is opened.
Control logic: Enabling a system if it receives a manual "start" signal or an automatic signal.

Basic circuit example

Example circuit: Two push-buttons (S1, S2) with pull-down resistors (R1, R2) control the A and B inputs of the gate. The Y output drives an LED with a resistor (R3). If either of the two buttons is pressed, the LED turns on.

Circuit connections:

VCC = +5V to pin 14
GND to pin 7
10kΩ resistors keep inputs at "0" when buttons are open.
Pressing S1 or S2 causes the 74LS32 to produce a "1" at the output.
The LED lights up with a 220Ω or 330Ω resistor.

Important Considerations for Use

Voltage and Power

Correct voltage: The 74LS32 must operate near 5V (4.75–5.25V). It is not suitable for 3.3V (use the HCT variant instead).
Power connections: Always connect VCC to pin 14 and GND to pin 7.

Current Handling

Low outputs: Can sink up to 8 mA.
High outputs: Limited to -0.4 mA, should not drive heavy loads in high mode.
Fan-out: Can drive up to 10 standard TTL loads.

TTL Inputs

Do not leave floating: Unconnected TTL inputs behave like a logical "1", but it is bad practice. Always use pull-up or pull-down resistors.
Logic levels: "HIGH" is recognized above 2V.
3.3V compatibility: To connect a 3.3V output to an input, it is safer to use a 74HCT32.

Comparisons with Other TTL Gates

74LS08: 4 AND gates. The output is "1" only if both inputs are "1".
74LS04: 6 inverters (NOT). Inverts the input signal.
74LS86: 4 XOR gates. The output is "1" if the inputs are different.
CMOS families (74HC, 74HCT): Operate over a wider voltage range (2–6V) and are more power-efficient.

Practical Resources

Datasheet SN74LS32 (Texas Instruments): [Quadruple 2-Input Positive-OR Gates]
Datasheet SN74HC32 (Texas Instruments): [Quadruple 2-Input OR Gates - CMOS]
Simulations: Tinkercad or Falstad for testing OR gates with the 7432.
Software: Proteus, Multisim, and other circuit simulators include the 7432 family.

Frequently Asked Questions (FAQ)

What gate is the 7432? The 7432 (or 74LS32) is an integrated circuit with four two-input OR logic gates.

What is the truth table for the 74LS32? Each OR gate follows the table: A=0,B=0 → Y=0; 0,1→1; 1,0→1; 1,1→1. The output is "1" if input A or input B is "1".

What voltage does the 74LS32 operate at? It operates at a standard TTL voltage, typically 5V (range 4.75–5.25V). For 3.3V systems, it is better to use a 74HCT32.

Can I use a 74HC32 instead of a 74LS32? Yes. The 74HC32 is the CMOS version, operating between 2V and 6V. In a 5V system, it is a direct replacement, with lower consumption and better output current capability.

How do I connect the 74LS32 on a breadboard with Arduino? Connect VCC to +5V (pin 14) and GND to 0V (pin 7). Use the inputs to read signals from sensors or buttons, and the outputs to activate LEDs or other parts of your circuit. Remember to use pull-down/up resistors on the inputs if they might be left unconnected.

What do SN74LS32, 74HC32, etc., mean? The prefix indicates the logic family: 74LS32 is TTL Low-Power Schottky; 74HC32 is High-speed CMOS; 74HCT32 is CMOS with TTL-compatible inputs. All perform the same OR function but differ in voltage, speed, and consumption.

References: Information is based on official datasheets from Texas Instruments and technical sources to ensure accuracy.