Understanding the PCF8584P’s Role
Before jumping into the project, it’s crucial to grasp the significance of the PCF8584P. Manufactured by NXP (originally Philips), the PCF8584P is a stand-alone I2C bus controller that acts as a bridge between a microprocessor and I2C devices. It comes in a 20-pin DIP package, making it perfect for breadboarding and prototyping. The chip supports both master and slave modes and is capable of generating the required I2C clock and data signals. This feature makes it incredibly handy when your main processor doesn’t natively support I2C or if you're trying to offload bus timing responsibilities.In our project, the PCF8584P becomes the central communication translator. It sits between a modern I2C host—like a Raspberry Pi, Arduino with I2C capabilities, or even a modern sensor array—and an old parallel device, such as a vintage printer or parallel port LCD. The PCF8584P accepts I2C commands and translates them into parallel data that the legacy device can understand.
Project Objective
Our mission is to build an I2C-to-Parallel bridge that will allow a Raspberry Pi to control a parallel-interface dot-matrix printer. These types of printers are typically designed for old computers with parallel ports, and they’re surprisingly robust. By repurposing them for a new era, we can turn them into message printers for IoT applications, art projects, or real-time logging devices.Components Needed
To bring this project to life, here is a breakdown of the key components:● PCF8584P – the I2C controller IC that will translate serial data into parallel output
● Raspberry Pi – acting as the I2C master controller
● Dot-Matrix Printer – any parallel-port capable printer should work, preferably with documentation or known pinout
● 74LS245 or equivalent – for buffering the data lines going into the printer
● Breadboard and jumper wires – for prototyping the circuit
● 5V and 3.3V power supplies – depending on the voltage requirements of the different components
● Level shifter – for voltage compatibility between Raspberry Pi and PCF8584P
● Decoupling capacitors – to stabilize power supply to the IC
● Pull-up resistors – on the I2C lines (SDA and SCL)
● LEDs (optional) – to visually monitor data transmission and power states
Building the Hardware Interface
Start by placing the PCF8584P onto a breadboard, ensuring easy access to all pins. Wire the power and ground lines first, and connect decoupling capacitors near the power pins. This helps to ensure that the chip operates stably during data transmission.Next, connect the I2C lines. The Raspberry Pi’s GPIO pins provide the SDA (Serial Data Line) and SCL (Serial Clock Line). These lines need to be connected to the corresponding pins on the PCF8584P. Importantly, since the Raspberry Pi operates at 3.3V logic and the PCF8584P at 5V, a level shifter must be used to avoid damaging the Pi. Alternatively, opt for I2C-safe bidirectional level shifters designed for this exact scenario.
Pull-up resistors are necessary on both SDA and SCL lines—typically 4.7kΩ or 10kΩ connected to the 3.3V rail when working with the Raspberry Pi.
The parallel data output lines from the PCF8584P (usually labeled D0 through D7) should be routed to a buffer IC like the 74LS245. This buffer acts as a current amplifier and protection layer between the delicate outputs of the PCF8584P and the robust interface of the dot-matrix printer.
From the buffer’s output, wire the data lines to the printer’s parallel input pins. Most dot-matrix printers using the Centronics interface expect not only 8-bit data but also control signals such as STROBE and BUSY. The PCF8584P can be configured to handle some of these lines through its control register interface or, alternatively, with a few additional logic gates or a microcontroller to manage them.
Initial Testing and Power-Up
Once the wiring is complete, power up the entire setup. Use LEDs on the data lines to verify that communication occurs when you send test messages from the Raspberry Pi. It’s important to confirm that the PCF8584P is responding on the I2C bus. A basic I2C scanner program can help verify its presence.Check that the buffer IC is correctly passing signals from the PCF8584P to the printer, and ensure the printer acknowledges the data. If all goes well, the printer should make a mechanical sound—perhaps even printing a line of gibberish if data alignment isn’t perfect yet. That’s a good sign!
Fine-Tuning and Communication Logic
The next step is ensuring that the data sent over I2C is correctly formatted for the parallel device. The PCF8584P allows for various modes—like master transmit, master receive, and combined master-slave configurations. For this project, master-transmit mode is the most relevant, since our Raspberry Pi will be initiating the communication.Sending a string from the Raspberry Pi to the printer now involves three conceptual steps:
- The Pi formats a message and sends it via I2C to the PCF8584P.
- The PCF8584P receives the data and transfers it to its internal FIFO buffer.
- The buffered data is sent out in parallel format to the printer, one byte at a time, along with the necessary control pulses.
Integration into a Functional System
With the core communication working, it's time to think of applications. Here are a few ways this I2C-to-Parallel bridge can be used creatively:● Real-Time Thermal Printer for IoT Devices: Use the Raspberry Pi to collect sensor data (e.g., temperature, humidity, or motion detection) and periodically print logs via the dot-matrix printer.
● Retro Twitter Feed Printer: Have a script on the Pi fetch your latest tweets and send them over to the printer in a vintage teletype fashion.
● Art Project: Print out ASCII art or text-based visuals directly to a printer using data stored on the Raspberry Pi or received from another device on the I2C network.
● Logging Terminal for Microcontroller Experiments: Other I2C devices, such as a microcontroller, can send debug logs or event messages via the PCF8584P to the printer, turning it into a real-time hard-copy logger.
Housings and Final Assembly
Once testing is complete and the system functions reliably, consider moving it from the breadboard to a more permanent enclosure. Use a small project box to house the PCF8584P circuit and include secure connectors for the I2C lines, power input, and parallel output.Label the pins clearly and ensure good insulation between high-power and logic-level lines. If using the bridge in a workshop setting, mounting it on a small PCB and attaching it to a panel rack might make frequent usage more practical.
For an added layer of sophistication, integrate an OLED or LED display to show status messages like "Ready," "Printing," or "Error." This gives your project a polished feel and helps with diagnostics.
Lessons Learned and Final Thoughts
Working with the PCF8584P opens the door to interfacing I2C systems with older hardware that still uses parallel communication. Though the chip is not as popular today as it once was, its utility in bridging eras of electronics is unmatched.This project not only builds an I2C-to-Parallel bridge but also teaches critical skills in hardware interfacing, signal conditioning, and timing analysis. It underscores how older components still have valuable roles in modern-day DIY electronics, especially when combined with flexible chips like the PCF8584P.
Best of all, this bridge can be adapted for many other parallel devices—not just printers. Think old LCDs, memory-mapped peripherals, or even legacy musical equipment. With a bit of creativity and elbow grease, the PCF8584P can become the cornerstone of your next great hardware hack.
Whether you're a collector of old tech or just enjoy solving intricate interfacing puzzles, this project offers a satisfying challenge and a rewarding payoff. Happy building!
US 23447 
BR 23203 
GB 13811 
CA 10852 
AU 10509 
VN 7007 
IN 5831 
IE 5104 
