Sixteen Solid State Relays 2A/24V 8-Layer Stackable HAT for Raspberry Pi
Sixteen Solid State relays with status LEDs and Normal Open contacts; RS485/MODBUS; Hardware Watchdog.
Overview
Compatible with all Raspberry Pi models from the Raspberry Pi Zero to Raspberry Pi 5, the Sixteen Solid State Relays HAT provides a compact and reliable solution for controlling up to 128 solid-state relay outputs from a single Raspberry Pi. Unlike mechanical relays, solid-state relays have no moving parts, operate silently, and offer virtually unlimited switching life, making the card ideal for applications requiring frequent or continuous switching.
The card is software-compatible with the Sixteen Relays HAT, allowing existing applications to migrate without software changes. It can be stacked up to eight levels together with other Sequent Microsystems HATs, providing a scalable solution for high-channel-count industrial control systems.
- Sixteen SSR outputs, N.O. contacts, 2A / 24VAC — 24VDC rating
- Unlimited electrical and mechanical endurance
- Stack up to eight cards for a total of 128 SSR outputs
- RS485 / MODBUS RTU interface
- Onboard hardware watchdog for automatic Raspberry Pi recovery
- Pluggable field-wiring connectors for 26–16 AWG wires
- 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.
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INTERFACES AND I/O
| I/O's | Communication | Software Integration |
|---|---|---|
| • Sixteen SSR Outputs (N.O. contacts) | • I2C Port to Raspberry Pi | • Command Line |
| • 2A / 24VAC — 24VDC contact rating | • RS485 / MODBUS Port | • Python Library |
| • Node-RED nodes | ||
| • CODESYS Driver | ||
| • OpenPLC Module | ||
| • Home Assistant | ||
| • Arduino Library | ||
| Other Features | ||
| • 8 bicolor LEDs showing status of groups of 8 relays | ||
| • Front-edge programmable pushbutton (GPIO 26) | ||
| • Reverse polarity protection on power supply | ||
| • Built-in relay self-test | • Pluggable connectors 26–16 AWG wires | |
| • On Board Hardware Watchdog | • Onboard resettable fuse 3A | |
| • Eight Level Stackable | ||
DESCRIPTION
The Sixteen Solid State Relays HAT is a drop-in software-compatible upgrade to the Sixteen Relays HAT, replacing mechanical contacts with solid state switches that have no moving parts and no finite cycle limit — ideal for any application where loads are switched frequently or continuously.
Mechanical relays wear out after approximately 1,000,000 operations. At a 1-second switching interval, that limit is reached in under two weeks. Solid state relays have no mechanical contacts, no moving parts, and no finite endurance limit — suitable for any switching frequency, indefinitely.
The Sixteen Solid State Relays Card is fully software-compatible with the Sixteen Relays HAT. It can be mixed in the same stack with all other Sequent Microsystems cards equipped with a processor, allowing flexible combinations of relay types and I/O cards on a single Raspberry Pi.
The integrated RS485 transceiver operates as a MODBUS RTU slave under Raspberry Pi control, or standalone — connected directly to a PLC or industrial controller without a Raspberry Pi required.
A pushbutton at the card edge routes to GPIO 26 (pin 37). Use it to trigger a safe Raspberry Pi shutdown or any application-defined command with a custom monitoring script.
The hardware watchdog monitors Raspberry Pi activity and automatically power-cycles the computer if the software becomes unresponsive, ensuring continuous operation in unattended deployments.
Bicolor LEDs are grouped along one edge of the board, with each LED indicating the state of a group of eight relays. A power LED confirms when power is applied. This layout provides at-a-glance status across all sixteen outputs without crowding the board.
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.
| 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) |
| TX | RS485 TX select | ON: Raspberry Pi drives RS485 directly |
| RX | RS485 RX select | ON: Raspberry Pi receives RS485 directly |
| TERM | RS485 termination | Enable on the last card in an RS485 chain to prevent signal reflections |
ELECTRICAL SPECIFICATIONS
| Power | |
|---|---|
| Power supply | 5V / 8A pluggable 2-pin connector with reverse polarity protection |
| Power consumption | 20 mA |
| Onboard resettable fuse | 3 A |
| SSR Contacts | |
|---|---|
| Contact configuration | N.O. only |
| Contact rating | 2.0A / 24VAC — 24VDC |
| Ron resistance | 60 mΩ typ. |
| Off-state leakage current | max. 1 μA |
| Turn On Time | 1.5 ms max. |
| Turn Off Time | 0.5 ms max. |
| Load Current | 2.5 A max. |
| Peak Load Current | 5 A (100 ms pulse) |
| Electrical and Mechanical endurance | Unlimited |
POWER REQUIREMENTS
Power supply: The Sixteen Solid State Relays Card requires 5V to operate. It can be powered from the Raspberry Pi over the GPIO bus or from its own 2-pin pluggable power connector. The board draws 20mA. If power is applied to the board connector, no separate Raspberry Pi power supply is needed. The power input is protected against accidental reverse polarity connection.
PLUGGABLE CONNECTORS
All relay outputs and the RS485 port connect to 3.5mm pitch pluggable screw terminal connectors, 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.
RELAY SELF-TEST
The card can be tested before installation by running a self-test command from the command line. The card will cycle each relay on and off at 0.5-second intervals. The lighting of the LEDs confirms that all relays are functioning.
16relind <id> test
COMMUNICATION INTERFACES
HARDWARE WATCHDOG
The Sixteen Solid State Relays 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 | |
|---|---|
| Initial timeout period | Configurable — allows time for Raspberry Pi to boot and start the application |
| Running timeout period | Configurable — normal operating timeout |
| Off period | Configurable — duration the Raspberry Pi power is cut when timeout triggers |
| Reset counter | Stored in non-volatile flash; can be read or cleared at any time |
For a full list of watchdog commands, run: 16relind -h
COMPATIBILITY
| Interface | I2C |
| GPIO used | GPIO2 (SDA), GPIO3 (SCL) — 2 pins only; remaining 24 GPIO pins stay free |
| Max stack | 8 cards — up to 128 SSR outputs; different Sequent HATs can be freely mixed |
| 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.
Running the Update
~$ cd ~/16relind-rpi/update/
~/16relind-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/16relind-rpi/tree/master/update/README.md
DOWNLOADS
| User's Guide (PDF) | Schematics (PDF) | CAD | Software & Integrations |
|---|---|---|---|
| User's Guide V1.0 | Hardware Schematic V2.0 | 3D Printing Enclosure | Command Line |
| Hardware Schematic V3.0 | 2D CAD Drawing | Python Library | |
| 3D STEP Model V2 | Node-RED Nodes | ||
| MODBUS Interface | |||
| CODESYS Driver | |||
| Home Assistant Integration | |||
| OpenPLC Module | |||
| Arduino Library |
COMPLIANCE
RoHS and REACH Compliance Declaration
WHAT'S INCLUDED
When you purchase the card you will receive the following items:
| 1. Sixteen Solid State Relays HAT for Raspberry Pi |
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| 2. Mounting Hardware | |
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| 3. Connector Plugs for all Outputs and RS485 | |
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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/16relind-rpi.git~$ cd /home/pi/16relind-rpi~/16relind-rpi$ sudo make install~/16relind-rpi$ 16relind
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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