Project Hub /Basic Analog & Power Electronics/Discrete & Component Electronics/ATmega328 Analog I/O Port Expander Using I2C Bus

Intermediate

ARDUINO

₹500 – ₹1,500

3 – 6 Hours

Partial Kit

ATmega328 Analog I/O Port Expander Using I2C Bus

This project explains how to interface multiple PCF8591 ADC/DAC converters with an ATmega328 microcontroller using the I2C bus to expand the available analog inputs and outputs, displaying the results on an LCD screen.

Originally published on ElectronicsForU

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

We don't carry yet: LCD (generic / unspecified)
ATmega / AVR chip
ADC / DAC (ADS1115 / MCP3008 / MCP4725)
Custom PCB / PCB Fab

Browse all components

How It Works

This project expands the analog input and output capabilities of an Arduino Uno using an ATmega328 microcontroller by leveraging the I2C communication bus. Because a standard microcontroller offers a limited number of built-in analog pins, the circuit connects five PCF8591 integrated circuits in parallel along the same I2C bus lines, utilizing unique hardware addresses for each IC. The ATmega328 acts as the master device, querying each PCF8591 module sequentially to read multiple analog sensor inputs via their internal Analog-to-Digital Converters (ADCs) and control analog outputs via the Digital-to-Analog Converters (DACs). Using the Arduino IDE and the Wire library, the microcontroller manages the complex communication protocol required to address and request data from these external converter chips. Once the ATmega328 processes the incoming analog readings from the network of PCF8591 units, it formats the data and drives a 16x2 LCD display using the LiquidCrystal library, allowing users to view real-time feedback from numerous analog sources simultaneously. The entire system is powered by a stable 5V DC power supply, with 10k ohm pull-down resistors ensuring proper signal stabilization on the I2C data and clock lines. Through this multi-drop bus topology, undergraduate engineering students can effectively overcome microcontroller hardware bottlenecks and scale up sensor networks without needing a larger processor.

Why Build This

Overcome microcontroller pin limitations by multiplexing multiple analog sensors onto a single two-wire I2C interface for scalable industrial monitoring panels.

Gain hands-on engineering experience designing multi-device bus architectures using the PCF8591 ADC/DAC IC alongside an ATmega328.

Build a practical multi-channel data acquisition system capable of processing and visualizing complex analog inputs on a local LCD screen.

Real-World Application

Sensor data acquisition systems, industrial monitoring panels requiring numerous analog sensors, and multi-channel data loggers.

Skills You'll Learn

I2C bus communication protocol

multi-device address configuration

analog-to-digital and digital-to-analog conversion

microcontroller pin expansion techniques

LCD screen interfacing

sensor data acquisition

Safety Precautions

Ensure correct 5V power supply polarity and connections to avoid damaging the ICs.

Technology Tags

ATMEGA328

PCF8591

I2C

ADC

DAC

LCD

ARDUINO IDE

PCB DESIGN

Frequently Asked Questions

How can five identical PCF8591 chips share the same I2C bus without data collisions?

Each PCF8591 chip features configurable hardware address pins (A0, A1, A2). By wiring these pins to unique combinations of high and low logic states, you give each IC a distinct address on the I2C bus.

Why are 10k ohm resistors needed in this circuit?

The 10k ohm resistors act as pull-down resistors (or pull-ups depending on specific bus line implementation) to ensure stable logic levels and reliable signal transmission on the I2C communication lines.

Can I use a standard 3.3V power supply instead of a 5V DC supply?

The components specified are designed to operate on a 5V DC power supply; using a 3.3V supply may cause logic level mismatches or improper operation of the ATmega328 and the PCF8591 modules.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

PRJ-00277