https://github.com/yamil-serrano/74hc165-microcontroller-input-expansion
Expand the number of digital inputs available on an any microcontroller, using just 3 GPIO pins and a 74HC165 shift register.
https://github.com/yamil-serrano/74hc165-microcontroller-input-expansion
74165 esp8266 microcontroller shift-register
Last synced: about 1 month ago
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Expand the number of digital inputs available on an any microcontroller, using just 3 GPIO pins and a 74HC165 shift register.
- Host: GitHub
- URL: https://github.com/yamil-serrano/74hc165-microcontroller-input-expansion
- Owner: Yamil-Serrano
- License: mit
- Created: 2025-05-21T00:59:46.000Z (about 1 year ago)
- Default Branch: main
- Last Pushed: 2025-07-30T01:36:05.000Z (11 months ago)
- Last Synced: 2026-03-11T02:20:54.548Z (3 months ago)
- Topics: 74165, esp8266, microcontroller, shift-register
- Language: C++
- Homepage:
- Size: 15.6 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE.md
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README
# 74HC165-Microcontroller-Input-Expansion
This project explores how to use the **74HC165 shift register** to expand the number of digital **inputs** available on an **ESP8266**, using only 3 GPIO pins. It’s built with **PlatformIO**, but it’s also compatible with the **Arduino IDE**.
The example reads 8 parallel inputs (like buttons or switches) and prints their values to the serial monitor. It uses **parallel-to-serial** communication to achieve input expansion with minimal pin usage.
---
### 🧩 This Project is Part of a Shift Register I/O Expansion Series
This repository is the **second part** of a series exploring how to expand the I/O capabilities of microcontrollers using shift registers:
- **Part 1**: [74HC595-Microcontroller-Output-Expansion](https://github.com/Yamil-Serrano/74HC595-Microcontroller-Output-Expansion)
- **Part 2**: [74HC165-Microcontroller-Input-Expansion (this repo)](https://github.com/Yamil-Serrano/74HC165-Microcontroller-Input-Expansion)
In Part 1, I explain how to use the 74HC595 to control 8 outputs using serial data.
This project is the *reverse* — it reads multiple digital inputs using the **74HC165** via **parallel-to-serial** communication.
---
## What You'll Learn
- What the 74HC165 does and how it works
- How to read multiple digital inputs using a shift register
- How to connect the 74HC165 to an ESP8266
- How to use clock, latch, and data pins to capture and shift input states
---
## How It Works
The **74HC165** reads 8 parallel inputs (D0–D7) and shifts them out serially through a single `QH` pin. You control the data flow using 3 pins:
- **PL (Parallel Load)**: Captures the current state of the input pins
- **CLK (Clock)**: Shifts bits one by one to the output
- **QH**: The serial output line, connected to the ESP8266
By toggling these lines, you can read 8 (or more, if cascaded) inputs using just a few GPIOs.
---
## Hardware Used
- ESP8266 (NodeMCU / Wemos D1 mini)
- 74HC165 Shift Register
- Breadboard + Jumper Wires
- Push Buttons or Switches
- Optional: Pull-down resistors (10kΩ)
---
## Wiring Table
| 74HC165 Pin | Connected To (ESP8266) | Purpose |
|-------------|-------------------------|-----------------|
| QH (9) | D5 (GPIO14) | Serial Data Out |
| CLK (2) | D2 (GPIO4) | Clock |
| PL (1) | D1 (GPIO5) | Parallel Load |
| CE (15) | GND | Enable (Active Low) |
| GND | GND | Ground |
| VCC | 3.3V or 5V | Power Supply |
| D0–D7 | Input Devices (Buttons) | Input Pins |
> ⚠️ Remember to connect **pull-down resistors** on each button or input line to ensure a clean LOW signal when not pressed.
---
## Code Overview
The `readShiftRegister()` function handles:
1. Loading the inputs by pulsing `PL` LOW then HIGH
2. Shifting bits out by toggling the `CP` clock pin
3. Reading each bit from `QH`
See `src/main.cpp` for the full implementation.
---
## Diagram
---
## License
This project is licensed under the MIT License – see the [LICENSE](LICENSE.md) file for details.
---
## Contact
If you have any questions or suggestions, feel free to reach out to me:
GitHub: [Neowizen](https://github.com/Yamil-Serrano)