Eight Relays Eight Inputs for Raspberry Pi Back Panel

This industrial-grade Eight Relays Eight Inputs Raspberry Pi I/O module features eight high-current relays and eight opto-isolated 24V digital inputs, making it ideal for factory automation, process control, and remote monitoring applications. Designed for seamless integration with the Raspberry Pi Back Panel, it supports MODBUS RTU over RS485, OpenPLC, and CODESYS. Engineered for dependable performance in demanding industrial settings, this stackable relay and input board is perfect for scalable industrial control systems.

FEATURES

Key Features

• 8 High-Current Relays
  Four relays rated at 4A/250VAC and four at 8A/48VAC for reliable switching of high and low voltage loads.

• 8 Opto-Isolated 24V Digital Inputs
  PNP inputs with 24V active-high logic for robust industrial signal compatibility.

• Seamless Raspberry Pi Integration
  Plugs directly into the Raspberry Pi Back Panel — no additional wiring or hardware needed.

• Expandable Stack Design
  Stack up to 8 identical modules horizontally for larger projects.

• MODBUS Support via RS485
  Integrated RS485 port allows MODBUS RTU communication for easy industrial integration.

• Real-Time Status LEDs
  Input and output LED indicators provide immediate visual feedback.

• Built-in OLED Display
  128×32 dot matrix screen for displaying system status, messages, or sensor values.

• Cross-Platform Software Support
  Includes Python library and command-line tools for rapid development.

• OpenPLC & CODESYS Compatible
  Industrial-grade compatibility with both OpenPLC and CODESYS environments.

• No Export Restrictions
  ECCN classification EAR99 — freely exportable under U.S. regulations.

DESCRIPTION

Part of the HOP (Hardware On Panel) family developed by Sequent Microsystems, the Eight Relays Eight Inputs I/O card is designed to integrate seamlessly with the Raspberry Pi Back Panel. Up to eight HOP cards—of any type—can be installed on a single Back Panel, offering maximum flexibility for industrial automation applications.

This model features eight high-performance relays:

• Four relays support medium current (4A) at high voltage (up to 250VAC)

• Four relays handle high current (8A) at medium voltage (up to 48VAC or 24VDC)
  All relay normally open (N.O.) contacts are routed to the card’s heavy-duty pluggable connector for secure and efficient wiring.

Eight optically isolated digital inputs support active-high (PNP) signals from 3V to 24VAC/DC and are routed to spring-loaded connectors on the Back Panel for easy integration.

Sixteen onboard LEDs display the real-time status of each input and output. Additional indicators show board power and signal any error condition.

An RS485 port enables external PLC or industrial controller communication using the industry-standard MODBUS RTU protocol.

 

• Power Supply: 5V 10mA; 24V 120mA Back Panel provided
  
• Relays 1-4: N.O. contacts, 4A/250VAC/24VDC
• Relays 5-8: N.O. contacts  8A/48VAC/24VDC
• Electrical endurance: minim 105 cycles at 1,800 operations per hour, full load
• Mechanical endurance: minim 107 cycles at 18,000 operations per hour, no load
• Inputs: 3750V Isolation between inputs and outputs

DOWNLOADS

Hardware Schematic V1.0

2D DXF Mechanical

3D STEP Model

3D Printable Enclosure

SOFTWARE

QUICK START

1. Plug the Eight Relays Eight Inputs card on the Back Panel for Raspberry Pi and power up the system.
2. Enable I2C communication on Raspberry Pi using raspi-config.
3. Install the software from github.com:

• ~$ git clone https://github.com/SequentMicrosystems/8rel8in-rpi.git
• ~$ cd /home/pi/8rel8in-rpi
• ~/8relind-rpi$ sudo make install
• ~/8relind-rpi$ 8rel8in

FAQ

Q: What Raspberry Pi models are compatible with this card?
A: The card is compatible with all 40-pin Raspberry Pi models, including Pi 4, Pi 3, Pi 2, and Pi Zero.

Q: How are the inputs isolated?
A: Each input is optically isolated and supports both 24VAC and 24VDC signals for maximum industrial compatibility.

Q: What is the maximum current and voltage the relays can switch?
A: The relay ratings are determined by PCB layout. Refer to the datasheet for exact current and voltage limits per channel.

Q: How is the stack level determined?
A: Stack level is automatically assigned based on the slot the card is plugged into on the Back Panel via ID0–ID2 pins.

Q: What does the watchdog function do?
A: If the Raspberry Pi fails to communicate over I²C in a set time, the watchdog cuts power for 10 seconds to trigger a system reset.

Q: What is the purpose of the Panic function?
A: The Panic input resets all outputs to their predefined default states for emergency shutdown or fail-safe scenarios.

Q: How is the card tested?
A: A command-line test cycles each relay on/off at 0.5-second intervals, confirmed by clicking sounds and LED activity.

Q: Can multiple cards be used together?
A: Yes, up to 8 cards can be stacked using the Back Panel. Each card auto-assigns its ID for seamless expansion.

Q: Is there a display on the card?
A: Yes, it features a 128×32 dot-matrix display for status, self-test, and error messages.

Q: How is communication with the Pi handled?
A: Communication is via I²C using SDA and SCL lines on the 2×20 GPIO connector.