Multichemistry Watchdog HAT with UPS Battery Backup for Raspberry Pi
Supports Li-Ion, Li-Poly, Li3PO4, LiFePO4, Na-Ion batteries; 5V or 10-24V Power Supply
Overview
Watchdog HAT with UPS battery backup and multi-chemistry 18650 battery support for Raspberry Pi. The Multichemistry Watchdog combines a software-selectable battery charger, high-current step-up/step-down converters, and an intelligent hardware watchdog to protect mission-critical systems and keep them running through power outages.
- Automatically power-cycles Raspberry Pi after software lock-up
- Two 18650 battery sockets for UPS backup — prevents SD card damage during power outages
- Multi-chemistry support: Li-Ion, Li-Poly, Li₃PO₄, LiFePO₄, and Na-Ion cells
- Software-settable charge voltage limit from 3.5 V to 4.4 V
- Enhanced converters: 4A continuous / 5A peak — designed for Raspberry Pi 5
- Wide power input: 5V via USB-C or 3.5mm pluggable connector, or 10–24V on a dedicated connector
- Uses only I2C bus (address 0x30) — leaves GPIO pins available
- Works with any Raspberry Pi from Zero to 5
- ECCN Code EAR99
Software
Command line and Python library available for all watchdog functions.
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INTERFACES AND I/O
| I/Os | Communication | Software Integration |
|---|---|---|
| • Two Li-Ion 18650 Battery Sockets | • I2C Port (address 0x30) | • Command Line |
| • USB-C 5V Power Input | • GPIO11 Reset Toggle (optional) | • Python Library |
| • 5V 3.5mm Pluggable Power Input | ||
| • 10–24V 3.5mm Pluggable Power Input | ||
| • Charge and Standby Status LEDs | ||
| • Onboard Reset Push-Button | ||
| Other Features | ||
| • Software-selectable battery chemistry: Li-Ion, Li-Poly, Li₃PO₄, LiFePO₄, Na-Ion | ||
| • Software-settable charge voltage limit: 3.5 V, 3.6 V, 3.7 V, 4.05 V, 4.1 V, 4.2 V, 4.35 V, 4.4 V | ||
| • 4A continuous / 5A peak step-down converter (input → Raspberry Pi) | ||
| • 4A continuous / 5A peak step-up converter (battery → Raspberry Pi) | ||
| • Enhanced battery charger up to 700mA charging current | • Battery overheating protection | |
| • Charging stoppable via software command | • Onboard resettable fuse and reset pushbutton | |
| • ECCN Code EAR99 | ||
DESCRIPTION
The Multichemistry Watchdog HAT provides the safety required by mission-critical Raspberry Pi installations, combining UPS battery backup and an intelligent hardware watchdog in a single compact HAT. Its software-selectable chemistry and high-current converters make it the right choice for demanding applications including Raspberry Pi 5.
Default 120-second timeout automatically power-cycles the Raspberry Pi on software lock-up, resetting not only the Pi but any peripheral attached to it. Reset can be triggered via I2C command or by toggling GPIO11 (Pin 23).
Two 18650 batteries (not provided) keep the Raspberry Pi running through power outages, preventing SD card corruption. Both sockets must be populated — the board does not operate with a single cell. The processor cuts power at 2.8 V to prevent over-discharge damage.
Charge voltage limit is software-settable from 3.5 V to 4.4 V, covering Li-Ion, Li-Poly, Li₃PO₄, LiFePO₄, and Na-Ion 18650 cells. Charging can be stopped at any time via a software command. Always set the charge voltage according to the battery manufacturer's datasheet.
Accepts 5V via USB-C or a 3.5mm pluggable connector, or 10–24V industrial supply on a separate connector. The card delivers up to 4A continuous and 5A peak to the Raspberry Pi over the GPIO bus — no separate Raspberry Pi power supply required.
Hardware self-check runs at every power-up. The onboard LED flashes rapidly (5×/s) if a fault is detected, or slowly (1×/s) for normal operation. The LED turns on when the watchdog resets the Raspberry Pi, and off when the Raspberry Pi is powered down for a specific interval.
The onboard pushbutton can be read by the local processor to interrupt the Raspberry Pi, enabling shutdown or reset without a keyboard and monitor. A 2-pin jumper parallel to the button permits installation of an external pushbutton when the Raspberry Pi is in an enclosure.
TECHNICAL DETAILS
CARD LAYOUT
MECHANICAL SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
| Power | |
|---|---|
| Power supply | 5V via USB-C or 3.5mm pluggable connector; 10–24V via separate 3.5mm pluggable connector |
| Output to Raspberry Pi | 5V / 4A continuous, 5A peak |
| Onboard resettable fuse | Yes |
| Step-Down Converter (Input → Raspberry Pi) | |
|---|---|
| Continuous output current | 4 A |
| Peak output current | 5 A |
| Step-Up Converter (Battery → Raspberry Pi) | |
|---|---|
| Continuous output current | 4 A |
| Peak output current | 5 A |
| Battery Charger | |
|---|---|
| Maximum charging current | 700 mA |
| Charge voltage (software-selectable) | 3.5 V, 3.6 V, 3.7 V, 4.05 V, 4.1 V, 4.2 V, 4.35 V, 4.4 V |
| Overheating protection | Yes |
| Battery | |
|---|---|
| Battery type | 18650 (×2 sockets, both required) |
| Under-voltage cutoff | 2.8 V |
| Recommended user shutdown voltage | 3.0 V |
| Ambient operating temperature | −40 °C to 85 °C |
POWER REQUIREMENTS
Power supply: The Multichemistry Watchdog HAT can be powered by 5V or 10–24V power supplies. Five volts can be provided through a USB Type-C port or a 3.5mm pluggable connector. Ten to 24V can be provided on a separate pluggable connector. Important: In order to operate, the watchdog must supply the power to the Raspberry Pi — the Pi must be powered through the watchdog for both UPS and watchdog functions to operate.
BATTERY OPERATION
Two 18650 batteries (not provided) can keep the Raspberry Pi running for hours, assuring continuous operation during power outages. Both sockets must be populated — the board does not work with a single battery. When running on battery power, the watchdog processor monitors the battery voltage. To prevent permanent damage due to over-discharging, the processor cuts off power to the Raspberry Pi when the battery drops below 2.8 V. A software command is available to monitor the battery voltage. It is strongly recommended that the Raspberry Pi performs a self-shutdown when the battery voltage drops below 3.0 V.
Multi-Chemistry: The charge voltage limit is software-settable via command line to 3.5 V, 3.6 V, 3.7 V, 4.05 V, 4.1 V, 4.2 V, 4.35 V, or 4.4 V. Always check with the battery manufacturer to find the correct end-of-charge voltage for your cells.
SELF-TEST
The Multichemistry Watchdog HAT has onboard hardware to self-check all major functions. The self-check is performed at each power-up. The onboard LED flashes rapidly (5 times per second) if a hardware error is detected, or slowly (1 time per second) to indicate normal functionality. The LED turns on when the watchdog resets the Raspberry Pi, and off when the Raspberry Pi is powered down for a specific time interval.
PUSH-BUTTON
The Multichemistry Watchdog HAT has an onboard pushbutton that can be read by the local processor, which in turn can interrupt the Raspberry Pi. The push button can be used to shut down or reset the Raspberry Pi without a keyboard and monitor. A 2-pin jumper parallel to the pushbutton permits installation of the pushbutton at a remote location when the Raspberry Pi is installed in an enclosure.
COMMUNICATION INTERFACES
HARDWARE WATCHDOG
The Multichemistry Watchdog 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 (default 120 seconds) |
| Off period | Configurable — duration the Raspberry Pi power is cut when timeout triggers (default 10 seconds) |
| Reset counter | Stored in non-volatile flash; can be read or cleared at any time |
| Reset trigger | I2C command or GPIO11 toggle (Pin 23 on the GPIO connector) |
For a full list of watchdog commands, run: wdt -h
COMPATIBILITY
| Interface | I2C |
| GPIO used | GPIO2 (SDA), GPIO3 (SCL); GPIO11 (Pin 23) optional for watchdog reset — remaining GPIO pins stay free |
| Max stack | 1 card (fixed I2C address 0x30) |
| 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 ~/wdt-rpi/update/
~/wdt-rpi/update$ ./update
Full instructions including recovery procedures are available at:
https://github.com/SequentMicrosystems/wdt-rpi/tree/master/update/README.md
DOWNLOADS
| User's Guide (PDF) | Schematics (PDF) | CAD | Software & Integrations |
|---|---|---|---|
| 2D CAD Drawing | Command Line | ||
| 3D-STEP-MODEL V2 | Python Library | ||
| GrabCAD 3D Model | Line Power Monitor Example |
COMPLIANCE
RoHS and REACH Compliance Declaration
WHAT'S INCLUDED
When you purchase the card you will receive the following items:
| 1. Multichemistry Watchdog HAT for Raspberry Pi |
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| 2. Mounting Hardware | |
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| 3. Connector Plugs for Power Inputs | |
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QUICK START
- Plug your card on top of your Raspberry Pi and power up the system from the watchdog.
- Enable I2C communication on Raspberry Pi using
raspi-config. - Install the software from GitHub:
~$ git clone https://github.com/SequentMicrosystems/wdt-rpi.git~$ cd /home/pi/wdt-rpi~/wdt-rpi$ sudo make install~/wdt-rpi$ wdt
The program will respond with a list of available commands. To read more about the CLI, please refer to the README file. You can also write your own application using the Python Library.
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