Smart Relays with Universal Inputs 8-Layer Stackable HAT for Raspberry Pi

Overview

Relay control and universal input hardware for Raspberry Pi for mission-critical home and industrial automation. The Smart Relays with Universal Inputs HAT combines four HALL-effect current-sensing relay outputs with four universal inputs that read either 10K thermistor temperature or dry-contact/opto-isolated digital signals, in a compact, stackable platform.

• Four relay outputs with HALL-effect current sensing, switching up to 8A at 240VAC or 24VDC
• Monitor load failure, compute load power, and limit load current from 1 to 8A
• Four universal inputs reading 10K thermistor temperature, or dry-contact/24V opto-isolated digital signals
• Extended input functions: transition counters, PPS counters, quadrature encoders, and PWM reading
• RS485/MODBUS interface — card controllable without Raspberry Pi
• Up to 8 cards stackable (32 relays + 32 inputs per Raspberry Pi)
• Works with any Raspberry Pi from Zero to 5

Works with Open Automation Software

Compatible with widely used tools for control, monitoring, and system integration.

INTERFACES AND I/O

DESCRIPTION

The Smart Relays with Universal Inputs HAT is the ideal solution for mission-critical projects where you must be 100% sure that your system works as expected, combining current-monitored relay switching with flexible input reading for Raspberry Pi.

TECHNICAL DETAILS

CARD LAYOUT

MECHANICAL SPECIFICATIONS

DIP SWITCH AND STACKING

The onboard six-position DIP switch configures both the stack address and the RS485 port behavior. Cards of different Sequent HAT types can be freely mixed in the same stack.

ELECTRICAL SPECIFICATIONS

POWER REQUIREMENTS

COMMUNICATION INTERFACES

RELAY SELF TEST

The card can be tested before installation by running a simple command from the command line. The card will cycle each relay on and off at 0.5 second intervals. The clacking noise of the relays and the lighting of the LEDs will assure that all relays are functioning.

EXTENDED INPUT FUNCTIONS

The card's local processor enables the following extended input capabilities on all channels:

• Transition counters to 4kHz on all inputs
• Input counters with cumulative or PPS (pulse per second) reading up to 4kHz
• 2× Quadrature encoder inputs reading up to 4000 PPS
• PWM inputs on each channel, reading both the fill factor and the frequency
• 1% resolution on PWM inputs up to 100Hz, 5% resolution up to 500Hz

CURRENT SENSING & LOAD MONITORING

HALL-effect sensors on each relay output continuously monitor the load current. This lets you confirm the load is operating within its specified parameters, compute the load power, and limit the load current to any value from 1 to 8A — useful for detecting load failure or protecting downstream equipment from overcurrent conditions.

HARDWARE WATCHDOG

The Smart Relays with Universal Inputs HAT includes a hardware watchdog that ensures your system automatically recovers if the Raspberry Pi software becomes unresponsive. The watchdog is disabled at power-up and activates after it receives the first reset command from the Raspberry Pi.

For a full list of watchdog commands, run: 4rel4in -h

COMPATIBILITY

FIRMWARE UPDATE

The onboard microcontroller firmware can be updated in the field. The update tool downloads the latest firmware from Sequent Microsystems' servers and flashes it to the board over I2C.

Running the Update

~$ cd ~/4rel4in-rpi/update/

~/4rel4in-rpi/update$ ./update <id>

Replace <id> with the board stack address (0-7). Full instructions including recovery procedures are available at:

https://github.com/SequentMicrosystems/4rel4in-rpi/tree/main/update/README.md

DOWNLOADS

WHAT'S INCLUDED

When you purchase the card you will receive the following items:

1. Smart Relays with Universal Inputs Card for Raspberry Pi

2. Mounting Hardware
	Four M2.5×18mm male-female brass standoffs Four M2.5×5mm brass screws Four M2.5 brass nuts

3. Mating Connector Plugs
	Eight 3-pin female mating connector plugs Two 2-pin female mating connector plugs

QUICK START

1. Plug your card on top of your Raspberry Pi and power up the system.
2. Enable I2C communication on Raspberry Pi using raspi-config.
3. Install the software from GitHub:
   ~$ git clone https://github.com/SequentMicrosystems/4rel4in-rpi.git

   ~$ cd /home/pi/4rel4in-rpi

   ~/4rel4in-rpi$ sudo make install

   ~/4rel4in-rpi$ 4rel4in

The program will respond with a list of available commands. To read more about the cli, please refer to the README file. If you would rather use a different platform, you can access the same functionality through dedicated, ready-to-use integrations in the Downloads tab above.