8 HV and 8 LV Digital Inputs for Raspberry Pi I/O Back Panel

This industrial-grade 8 HV and 8 LV Digital Inputs Card features eight 240V and eight 24V opto-isolated AC/DC 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 input board is perfect for scalable industrial control systems.

FEATURES

• 16 opto-isolated inputs: 8× HV (24–240 VAC/DC) + 8× LV (3–24 VAC/DC, PNP)
• Connector routing: HV on card via 2×8 pluggable connectors; LV to Back Panel spring-loaded terminals
• Back Panel integration: plug-and-play with auto slot addressing; mix up to 8 HOP cards per panel; panels can be chained
• Diagnostics: per-channel status LEDs and 128×32 OLED for on-board feedback
• Industrial protocols: RS485 / MODBUS RTU (can operate without a Raspberry Pi)
• CAN Support via CANopen
  Integrated CAN interface enables reliable CANopen communication for seamless industrial networking and real-time device control.
• Software support: CLI & Python libraries; OpenPLC and CODESYS compatible
• Isolation & safety: opto-isolation on all inputs; clear HV/LV separation
• Compliance: ECCN EAR99

DESCRIPTION

The 8 HV and 8 LV Digital Inputs Card adds 16 opto-isolated digital inputs to the Raspberry Pi Back Panel for reliable field signal monitoring. It combines 8×LV inputs (3–24 VAC/DC, active-high/PNP) and 8×HV inputs (24–240 VAC/DC) with clear routing:

• LV inputs are mapped to the Back Panel spring-loaded terminals for fast, tidy wiring.
• HV inputs are brought out on the card’s 2×8 pluggable connectors for safe separation and serviceability.

Designed for industrial use, the 8 HV and 8 LV Digital Inputs Card features per-channel status LEDs and a 128×32 OLED for on-board diagnostics. Control it from the Raspberry Pi over I²C (leaving GPIOs free) using our CLI/Python libraries, or use the integrated RS485 / MODBUS RTU interface to connect directly to PLC/SCADA systems—no Pi required.

As part of the HOP ecosystem, the 8 HV and 8 LV Digital Inputs Card supports auto slot addressing and scales with your build: use up to eight HOP cards (any mix) per Back Panel, and chain panels for larger installations. The card is powered from the Back Panel rails, so no extra power wiring is needed.

WATCHDOG

When enabled, the on-board watchdog expects periodic “kicks” from the Raspberry Pi (or a MODBUS master). If the timeout expires, the card asserts the Back Panel reset line and the Back Panel cuts power to the Raspberry Pi for ~10 s, then restores it—ensuring automatic recovery from lockups. The watchdog is off by default and can be configured from the CLI/Python libraries.

STACK LEVEL

No DIP switches or jumpers required—the physical slot on the Back Panel defines the card’s stack level. The level is read at power-up and shown on the OLED (e.g., S1…S8). Software addressing uses this slot number, so you can move cards between slots without reconfiguration. Use up to eight HOP cards (any mix) per Back Panel; panels can be chained for larger systems.

INTERRUPT

Each HOP card can signal an interrupt to the Raspberry Pi via the Back Panel’s shared INT line (wired-OR, active-low). Typical events (e.g., input change, status/fault) are latched in firmware and cleared by reading the status register. In your application, attach an edge handler to the Raspberry Pi’s interrupt GPIO (default physical pin 37 / GPIO26, configurable in software) to react instantly without polling.

HV Inputs Pinout

Input Mapping (Back Panel Terminals)

Only LV inputs #1–#8 are on the Back Panel terminals. “+/P” = Line/Positive; “-/N” = Return/Negative.

• Power Supply: 5V 100mA;  Back Panel provided

DOWNLOADS

Hardware Schematic V1.0

User's Guide V1.0

2D DXF Mechanical

3D STEP Model

3D Printable Enclosure

SOFTWARE

QUICK START

1. Plug the 8 HV and 8 LV Digital 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/sequent-cli.git
• cd /home/pi/sequent-cli
• sudo make install
• sequent-cli 16in -h
  

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 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: 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.