When your design grows to include large keypads, rows of limit switches, or complex diagnostic dip-switches, you will quickly hit a wall with your microcontroller’s available input pins. While the 74HC595 handles expanding outputs, the 74HC165 is the industry-standard silicon solution for expanding inputs. It is an 8-bit Parallel-In/Serial-Out (PISO) shift register. Instead of wiring eight separate buttons back to eight precious GPIO pins on an Arduino or ESP32, you connect them all directly to this chip.
The operation is elegant and incredibly fast: you pull the Shift/Load pin LOW to take an instantaneous hardware “snapshot” of all eight inputs simultaneously. Then, your microcontroller uses a clock line to sequentially tick through the chip, reading those eight button states one after the other down a single serial data line. Because it features a dedicated serial input pin, you can easily chain multiple 74HC165 chips together in a daisy-chain configurationallowing you to read 16, 24, or even 64 individual buttons while still utilizing only 3 or 4 pins on your primary processor.
Key Features & Functional Advantages:
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8-Bit Input Expansion: Converts an 8-bit wide parallel input block into a clean, sequential serial data stream, freeing up massive amounts of microcontroller I/O.
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Instantaneous Parallel Loading: Asynchronous load overrides the clock completely, capturing a precise, simultaneous snapshot of all inputs without timing lag.
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Infinitely Cascadable: Features a dedicated serial inputpin to daisy-chain additional chips together, massively multiplying input capacity over the same SPI-like bus lines.
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Complementary Serial Outputs: Provides both standard serial output and inverted serial outputpins, granting excellent flexibility for varying downstream logic architectures.
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Breadboard Native (16-DIP): Standard 0.1-inch (2.54mm) pin pitch drops perfectly into standard solderless breadboards, prototyping perfboards, and 16-pin IC sockets.
Perfect For:
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Industrial Control Panels: The absolute standard hardware choice for monitoring dense arrays of status switches, selector dials, and emergency stops.
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Custom Keyboards & Matrix Scanning: Safely handles large macro pads, musical instruments, and gaming controllers without exhausting processor resources.
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CNC & Robotics Limit Switches: Pools multiple physical axis limit sensors and safety interlocks down into a tidy, manageable serial interface.
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DIP-Switch Reading Arrays: Perfect for reading multi-position hardware configuration switches on automated circuit boards during startup cycles.
Technical Specifications:
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Logic Family: 74HC (High-Speed CMOS)
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Logic Function: Parallel-In / Serial-Out (PISO) Shift Register
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Number of Input Bits: 8 Bits (Parallel Inputs)
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Output Configuration: Serial Output and Inverted Serial Output
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Operating Supply Voltage : 2.0V to 6.0V DC
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High-Speed Clock Frequency: Up to 26 MHz (Typical at 5V)
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Low Quiescent Power Draw: Typically ~2A at 25C
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Package / Case: 16-DIP (0.300″, 7.62mm width)
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Mounting Type: Through-Hole (PTH)
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