Building Automation 8-layer stackable HAT for Raspberry Pi with software selectable universal inputs, RS485 port, and real-time clock.

Building Automation 8-layer stackable HAT with green connectors and DIP switches for Raspberry Pi with universal inputs and outputs, real-time clock, and RS485 MODBUS port.

Building Automation 8-Layer Stackable HAT for Raspberry Pi with multiple green pluggable connectors and red DIP switch on PCB.

Building Automation 8-layer stackable HAT with universal inputs and TRIAC outputs for Raspberry Pi.

Building Automation 8-Layer Stackable HAT for Raspberry Pi with universal inputs, TRIAC and 0-10V outputs, RS485/MODBUS port, real-time clock, and hardware watchdog.

Building Automation 8-layer stackable HAT circuit board for Raspberry Pi with multiple universal inputs and outputs.

SKU: SM-I-002

Building Automation 8-Layer Stackable HAT for Raspberry Pi

Name: Building Automation 8-Layer Stackable HAT for Raspberry Pi
Brand: Sequent Microsystems
SKU: SM-I-002
Price: 100.0 USD
Availability: InStock

Eight universal inputs: 1K/10K Thermistors, 0-10V, Dry Contact; Four 24VAC outputs; Four 0-10V outputs; 1-Wire, RS485, RTC, Watchdog.

In stock

$100.00

Product variants

Overview

Building automation hardware for Raspberry Pi with software-selectable universal inputs, standard communication interfaces, and support for widely used control and monitoring systems. The Building Automation HAT combines universal analog and sensor inputs, TRIAC and 0-10V outputs, RS485/MODBUS, and 1-Wire interfaces in a compact, stackable platform for HVAC, lighting, and building management applications.

Eight software-selectable universal inputs: 0-10V, 1K/10K thermistors, or dry contact
Native RS485 / MODBUS and 1-Wire interfaces
Four TRIAC outputs for 24VAC load control and four 0-10V outputs for dimming
Up to 8 cards of each type can be stacked and mixed with other Sequent HATs for virtually unlimited I/O expansion
Designed for HVAC, lighting control, and building management systems

Works with Open Automation Software

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

INTERFACES AND I/O

I/O's	Communication	Software Integration
• Eight Universal Inputs:	• I2C Port to Raspberry Pi	• Command line
• 1K or 10K thermistors	• RS485/MODBUS Port	• Python Library
• 0-10V analog inputs	• 1-Wire Interface	• Node-RED nodes
• Dry contact/counter inputs		• CODESYS Driver
• Four AC TRIAC Outputs, 1A/24VAC		• OpenPLC Module
• Four 0-10V Outputs		• Home Assistant
• Four General Purpose LEDs		• Arduino
Other Features
• Software-selectable universal input configuration
• Wide range 12-36VDC or 24VAC power supply delivers 5V to Raspberry Pi
• 500Hz sample rate on 0-10V inputs	• Status LEDs on all Digital Inputs and Outputs
• Works with any Raspberry Pi from ZERO to 5	• Pluggable Connectors 26-16 AWG wires
• TVS Protection on all Inputs	• On Board Hardware Watchdog and fuse
• Real Time Clock With CR2032 Battery Backup	• Eight Level Stackable

DESCRIPTION

The Building Automation HAT provides everything needed to build HVAC, lighting, and building management systems with Raspberry Pi.

Universal Inputs

Eight universal inputs are software-selectable per channel — configure each one independently as a 0-10V analog input, a 1K or 10K thermistor, or a dry contact/counter input with no jumpers or DIP switches required.

TRIAC Outputs

Four AC TRIAC outputs switch 24VAC loads up to 1A for direct control of fans, dampers, and valves.

0–10 V Analog Outputs

Four 0-10V outputs provide proportional control of light dimmers, variable-speed drives, and other analog actuators.

RS485/MODBUS & 1-Wire

Connect to other building automation systems using the RS485/MODBUS port. Read up to 16 DS18B20 temperature sensors via the 1-Wire interface.

General Purpose LEDs

Four general purpose LED outputs display the state of any digital or analog channel.

Real-Time Clock

The Real-Time Clock with CR2032 battery backup keeps accurate time through power failures, making the card ideal for scheduled control and time-stamped event logging.

Hardware Watchdog

The hardware watchdog automatically power-cycles the Raspberry Pi if the software becomes unresponsive, ensuring continuous operation in unattended deployments.

Protection

TVS diodes on all inputs protect against ESD and transient spikes. An onboard resettable fuse protects against accidental shorts.

The card communicates over I2C using only two of the Raspberry Pi's GPIO pins, leaving the remaining 24 GPIOs free for user applications. Compatible with all Raspberry Pi versions from Zero to 5. Up to 8 cards of each type can be stacked on a single Raspberry Pi, and cards of different types can be freely mixed in the same stack. Three DIP switch positions (ID0, ID1, ID2) set each card's stack address.

TECHNICAL DETAILS

CARD LAYOUT

Building Automation 8-Layer Stackable HAT for Raspberry Pi

MECHANICAL SPECIFICATIONS

BAS Mechanical Dimensions

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.

Switch	Name	Function
ID0	Stack ID bit 0	Binary stack address bit 0 (LSB) — sets card level 0–7
ID1	Stack ID bit 1	Binary stack address bit 1
ID2	Stack ID bit 2	Binary stack address bit 2 (MSB)
RX	RS485 RX select	ON: Raspberry Pi receives RS485 directly
TX	RS485 TX select	ON: Raspberry Pi drives RS485 directly
TERM	RS485 termination	Enable on the last card in an RS485 chain to prevent signal reflections

ELECTRICAL SPECIFICATIONS

Power
Power supply	3.5mm Pluggable Connector, 12–36VDC or 24VAC
Power consumption	50 mA @ 24 V
Onboard resettable fuse	1 A

0–10 V Inputs
Maximum Input Voltage	12 V
Input Impedance	20 KΩ
Resolution	12 bits
Sample rate	500 sps
Full scale linearity	0.15%

Contact Closure Inputs
Maximum frequency	100 Hz

0–10 V Outputs
Minimum Output Load	1 KΩ
Resolution	0.1%
Full scale linearity	0.1%

Triac Outputs
Maximum Output Current	1 A
Output Voltage	24 VAC

POWER REQUIREMENTS

Power supply: The card requires an external 12–36VDC or 24VAC power supply connected to its own pluggable power connector. The card supplies 5V and up to 4A continuous, 5A peak to the Raspberry Pi over the GPIO bus, eliminating the need for a separate Raspberry Pi power supply. Operating current is 50mA at 24V.

PLUGGABLE CONNECTORS

All I/Os connect to heavy-duty 3.5mm pitch pluggable screw terminal connectors rated at 8A, accepting wire gauges from 26 to 16 AWG. Connectors can be unplugged from the board for convenient field wiring and debugging without disturbing the rest of the installation.

SELECTING THE UNIVERSAL INPUTS

The default setting of the Universal Inputs is 0-10V. In order to change it:

Make sure you have the latest software installed, instructions in the readme.
Run the command "megabas 0 incfgwr <channel> <value>", where:

channel = 1-8
value = 0 for 0-10V, 1 for 1K Thermistor, 2 for 10K Thermistor
value = 3 for Dry contact/Counter

For more info on the commands type "megabas -h incfgwr" and "megabas -h incfgrd"

FIELD CALIBRATION

All analog inputs and outputs are factory-calibrated. However, firmware commands allow the user to recalibrate the board or perform higher-precision calibration if required.

Calibration is performed using a two-point method. The selected calibration points should be placed as close as possible to the minimum and maximum values of the measurement range.

Input Calibration

To calibrate the inputs, the user must apply known analog reference signals. For example, calibrating the 0-10V inputs requires an adjustable 0-10V power supply; calibrating the thermistor inputs requires known precision resistors placed at the two ends of the measurement range.

Output Calibration

To calibrate the outputs, the user must:

Issue a command to set the output to a desired value.
Measure the actual output using a calibrated instrument.
Issue the corresponding calibration command to store the measured value.

Storage and Reset

Calibration values are stored in non-volatile flash memory, and the input transfer curve is assumed to be linear.

If an incorrect command or value is entered during calibration, a RESET command can restore the selected channel to its factory calibration values. After a reset, the calibration procedure can be repeated.

The following firmware commands are available for performing calibration:

CALIBRATE 0-10V INPUTS:                    megabas <id> adccal <channel> <value>
RESET CALIBRATION OF 0-10V INPUTS:         megabas <id> adccalrst <channel>
CALIBRATE 1K THERMISTOR INPUTS:            megabas <id> r1kcal <channel> <value>
RESET CALIBRATION OF 1K THERMISTOR INPUTS: megabas <id> r1kcalrst <channel>
CALIBRATE 10K THERMISTOR INPUTS:           megabas <id> r10kcal <channel> <value>
RESET CALIBRATION OF 10K THERMISTOR INPUTS: megabas <id> r10kcalrst <channel>
CALIBRATE 0-10V OUTPUTS:                   megabas <id> daccal <channel> <value>
RESET CALIBRATION OF 0-10V OUTPUTS:        megabas <id> daccalrst <channel>

COMMUNICATION INTERFACES

RS485 / MODBUS

The Building Automation HAT includes a standard RS-485 transceiver that can be accessed either by the onboard processor or by the Raspberry Pi. The operating mode is configured using the TX and RX switches on the SW1 DIP switch.

When TX and RX are set to ON, the Raspberry Pi communicates directly with any device that has an RS-485 interface. In this mode the card functions as a passive bridge, implementing only the hardware signal levels required by the RS-485 protocol. To use this configuration, the onboard processor must first release control of the RS-485 bus:

~$ megabas 0 rs485wr 0 0 0 0 0

When TX and RX are set to OFF, the card operates as a MODBUS RTU slave. Any MODBUS master — PLC, SCADA, or HMI — can read all inputs and control all outputs using standard MODBUS commands, with no Raspberry Pi required. A full list of supported MODBUS registers is available on GitHub.

In both modes, the onboard processor must be configured to either release or control the RS-485 signals accordingly. Refer to the command-line help for further details.

1-Wire Interface

The Building Automation HAT includes a standard 1-Wire bus for connecting digital temperature sensors. Up to 16 DS18B20 sensors can be connected in parallel on a single two-wire cable, covering large areas such as multi-zone HVAC systems or distributed monitoring installations. Sensors are accessible from the command line, Python scripts, Node-RED, and the MODBUS interface, making integration straightforward regardless of your software environment.

HARDWARE WATCHDOG

The Building Automation 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.

Watchdog Parameters
Default timeout	120 seconds
Initial timeout period	Configurable — allows time for Raspberry Pi to boot and start the application
Running timeout period	Configurable — normal operating timeout
Off period	10 seconds before power is restored
Reset counter	Stored in non-volatile flash; can be read or cleared at any time

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

COMPATIBILITY

Interface	I2C
GPIO used	GPIO2 (SDA), GPIO3 (SCL) — 2 pins only; remaining 24 GPIO pins stay free
Max stack	8 cards of each type; different Sequent HATs can be freely mixed with virtually no upper limit on total I/O
Compatible with	All Raspberry Pi versions from Zero to 5 (40-pin GPIO header)

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.

WARNING: Stop all processes that access the card (Node-RED flows, Python scripts, cron jobs) before starting a firmware update. Accessing the card during an update may corrupt the firmware.

Running the Update

~$ cd ~/megabas-rpi/update/

~/megabas-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/megabas-rpi/tree/master/update/README.md

DOWNLOADS

User's Guide (PDF)	Schematics (PDF)	CAD	Software & Integrations
User's Guide V3	Schematic V3.0	2D CAD drawing	Command Line
User's Guide V4	Schematic V4.1	3D STEP Model	Python Library
	Schematic V5.1		Node-RED nodes
			MODBUS interface
			CODESYS driver
			Home Assistant Integration

WHAT'S INCLUDED

When you purchase the Building Automation Card you will receive the following items:

1. Building Automation Card for Raspberry Pi

2. Mounting Hardware
	Four M2.5×19mm male-female brass standoffs Four M2.5×5mm brass screws Four M2.5 brass nuts

3. Connector Plugs for all Inputs and Outputs
	Four 8-pin female mating connector plugs for I/Os One 5-pin female mating connector plug for RS485 and 1-Wire One 2-pin female mating connector plug for power

QUICK START

Plug your card on top of your Raspberry Pi and power up the system.
Enable I2C communication on Raspberry Pi using raspi-config.
Install the software from GitHub:

~$ git clone https://github.com/SequentMicrosystems/megabas-rpi.git

~$ cd /home/pi/megabas-rpi

~/megabas-rpi$ sudo make install

~/megabas-rpi$ megabas

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

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BAS hat

I really like the board. Some of the documentation doesn’t line up perfectly with the website, probably from older revisions of the card, but nothing that’s caused any issues.

The boards work great and shipping is very fast! I use it with Codesys runtime for RPi, it isn’t free but well worth it for the feature and compatibility it adds.

Amazing!

I´ve used a few of these in my projects and they have worked flawless everytime! When I´ve needed help the support from Sequent Microsystems have been of the charts! I will for sure continue to use this and other products from Sequent Microsystem.

Fantastic product and support

I am assembling a pool controller, Bought the building automation card, 8 relay card and early version of the industrial watchdog. They were extremely helpful providing the watchdog card to run off 24 volt. Now with a single 24 volt power supply I power the entire stack. In my area, power can go out frequently. The watchdog’s battery keeps me running. I can read multiple thermistors for air water and enclosure temperature as well as a flow sensor and still have more inputs available. The relay card will be used to trigger some stenner pumps for muriatic and chlorine additions. Cards are top notch and support is great.

Great Product and Superb Support

I'm building an RPi pool control system using Node-Red and other open sourced software. I had a new version that has dip switches instead of the jumpers and it's not yet reflected in the data sheet. So I got ready to email and have a few day delay. But I saw the chat window and put in a quick question. To my surprise they answered in minutes! Wow!! I'm not an electronics wiz, I'm more of a user that's tech savvy enough to get myself in trouble. I had heard these people had superb customer support but I also thought yeah, yeah, yeah... Boy was I wrong it's definitely YES, YES, YES! It's for real!!

Thank you folks, anytime I need something you sell this is where I'll come first.

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