Eight MOSFETS 8-Layer Stackable HAT for Raspberry Pi

The Eight MOSFETS Stackable Card is an industrial-grade output expansion module designed to interface seamlessly with any Raspberry Pi model, from Zero to Pi 5. It features eight powerful MOSFET channels—four high-current (12 A @ 24 V DC) and four high-voltage (4 A @ 240 V DC)—making it ideal for controlling motors, solenoids, industrial relays, and lighting systems.

Each output is driven by an onboard processor capable of generating 1 kHz PWM signals for precise proportional load control. A robust RS485 port, connected to the local processor, allows the board to operate independently of the Raspberry Pi as a MODBUS RTU slave, enabling easy integration with PLCs and industrial controllers.

The board offers galvanic isolation between high-current and high-voltage channels, with built-in TVS and flyback diode protection to safeguard both the board and connected equipment. Configuration is simplified with DIP switches—no jumpers required. Status LEDs provide real-time feedback on all outputs.

The card uses only the I²C interface (selectable addresses 0x20–0x27 or 0x38–0x3F), leaving all Raspberry Pi GPIO pins available. Power can be supplied via a 5 V or 10–24 V DC input, with onboard regulation delivering up to 5 A to the Raspberry Pi. Heavy-duty, pluggable connectors support 24–12 AWG wires for secure field wiring.

Fully compatible with Sequent Microsystems' 8-layer stackable system, this card is engineered for scalability, reliability, and flexibility in industrial automation applications. All required mounting hardware is included, and open-source schematics are available for developers and integrators.

The Eight MOSFETS card offers flexible power input options to suit a wide range of industrial applications. It can be powered in one of two ways:

• 5 V Input: When a stable 5 V power supply is available, the card can be powered directly through the standard 5 V rail. In this mode, the Raspberry Pi and the card share the same 5 V supply
• 10–24 V DC Input: For industrial environments where 12 V or 24 V power is more common, the card accepts input voltages from 10 V to 24 V. An onboard DC-DC converter regulates this input down to 5 V to power the card and provide up to 5 A of regulated 5 V output to the Raspberry Pi. This eliminates the need for a separate Raspberry Pi power supply.

This dual-input flexibility ensures compatibility with both lab setups and industrial control panels, while simplifying wiring and reducing the number of external power supplies required.

POWER REQUIREMENTS

The 8-MOSFETS Card can be powered from either a 5 VDC supply or a 10–24 VDC industrial power supply. Separate power connectors are provided for each option.

Galvanically isolated DC-DC converters provide the gate-drive voltages required by both the high-current and high-voltage MOSFET output sections, ensuring reliable operation and electrical isolation between the output groups.

An onboard step-down power supply provides regulated 5 V power for the Raspberry Pi, delivering up to 5 A peak and 4 A continuous output current.

8-MOSFETS Card power consumption:

25 mA @ 5 VDC (excluding external loads and Raspberry Pi)

The 5 V power input is protected by a 7 A fuse and can handle input currents up to 8 A. The 10–24 VDC power input is protected by a 2.5 A fuse.

For maximum system reliability, the card can power the Raspberry Pi through the onboard watchdog circuit, allowing automatic recovery from software lockups by cycling power to the Raspberry Pi when required.

DIP SWITCH CONFIGURATION

A six-position DIP switch is used to configure the RS485 port source and to set the card’s stack position when multiple cards are installed.

STACKING MULTIPLE CARDS

Up to eight cards can be stacked on a single Raspberry Pi. Three positions of the configuration DIP switch—labeled ID0, ID1, and ID2—are used to set the stack level for each card. Cards can be installed in any order, as long as each one has a unique ID setting.

RS485/MODBUS PORT

The card features an RS485 port that can be driven either by the Raspberry Pi or by the onboard local processor. The selection is controlled using two DIP switch positions labeled TX and RX.

• DIP Switches OFF (default):
  The RS485 port is connected to the local processor. In this mode, the card functions as a MODBUS RTU slave, allowing any MODBUS master to read all inputs and set all outputs using standard MODBUS commands. A complete list of supported commands and register addresses is available on the project's GitHub repository
• DIP Switches ON:
  The RS485 port is connected to USART1 of the Raspberry Pi, and the card acts as a passive hardware bridge. In this mode, the Raspberry Pi can communicate with any external RS485 device, but the card itself does not interpret or respond to MODBUS commands. It only provides RS485-level signal conversion

  Before using this mode, you must instruct the local processor to release control of the RS485 bus using the following command:

  ~$ 8mosind [0] rs485wr 0 0 0 0 0

In both configurations, the RS485 data direction is managed by the local processor. Control of the RS485 TX enable signal depends on whether jumpers are installed or removed:

• Jumpers Installed: RS485 control is handed over to the local processor (for MODBUS slave mode).

• Jumpers Removed: RS485 TX/RX is fully controlled by the Raspberry Pi (for external MODBUS master communication).

Refer to the command-line utility help for more details on configuring RS485 behavior.

RS485 TERMINATOR

The last position on the DIP switch controls the RS485 line termination. Set it to ON if the card is the last device on the RS485 bus.

Improperly shutting down the Raspberry Pi by cutting power directly can lead to SD card corruption. To avoid this, a safe shutdown command should be issued before powering off. However, doing so typically requires a monitor, keyboard, and mouse connected to the Pi.

To simplify this process, a momentary pushbutton is provided at the edge of the card. This button is connected to pin 37 (GPIO26) and offers a convenient way to initiate a safe shutdown.

To use it, you'll need to write a script that monitors GPIO26. When the button is pressed and held for a predefined duration (e.g., 2–3 seconds), the script should issue a proper shutdown command to the operating system.

You can write your own application using the Command Line or Python Libraries provided. No programming is required if you use the Node-Red nodes provided. You can drag-and-drop the functional blocks to design your application. Examples are provided at GitHub.

The card can be tested prior to installation by running a simple command from the command line. During the test, each MOSFET is cycled on and off at 0.5-second intervals. The illumination of the corresponding LEDs confirms proper operation of all output channels. For additional verification, users can connect optional test loads to each channel to observe real switching performance and further validate hardware functionality.

The Smart Fan provides a stackable cooling solution for Raspberry Pi. Its on-board processor powers the fan just enough to maintain the preset temperature of the Pi. If the Eight MOSFETS card is used to drive multiple high current loads, a secondary Smart Fan can be installed on top of the card to provide adequate cooling.

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

The program will respond with a list of available commands.

Connect your load between pin 2 of any of the load connectors and the positive side of your external power supply. Connect the negative side of your external power supply to pin 1 of the output connectors. Turn on and off the load using the corresponding command.

FAQ

Q: What types of loads can the card control?
A: The card can control both high-current DC loads (up to 12 A @ 24 V) and high-voltage DC loads (up to 4 A @ 240 V), such as motors, solenoids, industrial relays, lighting systems, and resistive or inductive loads.

Q: What Raspberry Pi models are supported?
A: The card is compatible with all Raspberry Pi models featuring a 40-pin GPIO header, including Raspberry Pi Zero, 3, 4, and 5.

Q: Can multiple cards be stacked?
A: Yes, up to eight cards can be stacked on a single Raspberry Pi using DIP switch settings to assign a unique ID to each card.

Q: How are the stack levels configured?
A: Three DIP switch positions labeled ID0, ID1, and ID2 are used to assign each card a unique stack level. Cards can be installed in any order.

Q: What is the purpose of the RS485 port?
A: The RS485 port can be driven either by the local processor (MODBUS RTU slave mode) or by the Raspberry Pi (RS485 master interface). DIP switches select the signal source.

Q: Can the card operate without a Raspberry Pi?
A: Yes. In MODBUS RTU mode, the onboard processor handles communication, allowing the card to be controlled by any MODBUS-compatible PLC or industrial controller.

Q: How do I safely shut down the Raspberry Pi?
A: A reset/shutdown pushbutton is provided and connected to GPIO26 (pin 37). With a simple monitoring script, this button can trigger a safe shutdown when held.

Q: How is power supplied to the card and Raspberry Pi?
A: The card can be powered by either 5 V or 10–24 V DC. It includes an onboard regulator that provides up to 5 A of 5 V output to power the Raspberry Pi.

Q: Is there short-circuit or overcurrent protection?
A: Yes. The board includes a 2.5 A onboard fuse and TVS/diode protection on high-current and high-voltage outputs.

Q: Are jumpers required for configuration?
A: No. All settings are configured via DIP switches, simplifying setup and reducing error.

Q: Is the card open-source?
A: Yes. Schematics and documentation are open source and available on Sequent Microsystems' GitHub repository.

Q: How can I test the card before installation?
A: A built-in self-test mode can be initiated via a command-line utility. The test cycles all MOSFET outputs and confirms functionality through LED indicators