SBK SP1

SBK_SP1

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Open-source soft power switch module for learning and embedded electronics projects.

SBK_SP1 is a compact, reusable soft power switch module for battery-powered and low-voltage embedded systems.

A momentary push button, maintained switch, or external control can turn the system on. Once powered, a microcontroller can assert the HOLD input to keep the system running independently of the switch state.

Version 2.0 adds an onboard start button, a dedicated external SW input, and an independent SENS output. This allows the microcontroller to continue monitoring the external switch while holding its own power on, making graceful software-controlled shutdown possible.

Designed for breadboards, prototypes, and educational projects, SBK_SP1 provides an easy way to add soft power management to Arduino, ESP32, RP2040, ATtiny, STM32, and similar microcontroller-based systems.

Features

• Input voltage: 2–12 VDC
• Load current: up to 2 A
• High-side P-channel MOSFET switching
• MCU-controlled soft power latch
• Onboard power/start button
• External momentary button or maintained switch input
• Independent switch-state sensing
• Supports graceful MCU-controlled shutdown
• Ultra-low off-state current (< 1 µA typ.)
• Power input and output status LEDs
• Breadboard-friendly 2.54 mm pin header
• Open-source hardware
• Optimized for low-cost assembly using JLCPCB Basic components

Specifications

Pinout

The onboard push button is connected to the SW and SENS functions and can be used to start the module without an external switch.

Typical Application

Battery / Power Supply
         │
         │
        VIN
   ┌───────────┐
   │  SBK_SP1  │
   │           │
   │   VOUT    ├──────────> Embedded System Power
   │           │
MCU├─ HOLD <───┤ MCU output
   │           │
MCU├─ SENS ───>│ MCU input with pull-up
   │           │
   │    SW     ├──── Switch / Push Button ──── GND
   └───────────┘
         │
        GND

Operation

Power On

1. The user presses the onboard button or connects SW to GND.
2. The hardware immediately enables the high-side power MOSFET.
3. VOUT powers the microcontroller and load.
4. SENS goes LOW, allowing the microcontroller to detect the active switch.
5. The microcontroller boots and drives HOLD HIGH.
6. The module remains powered after a momentary button is released.

Power Hold

While HOLD is HIGH, the microcontroller keeps VOUT enabled independently of the state of SW.

Because SENS monitors the switch separately from the HOLD circuit, the microcontroller can continue detecting button presses, button releases, or changes in a maintained external switch while power remains latched.

Graceful Shutdown

With a maintained ON/OFF switch, SBK_SP1 can support a software-controlled shutdown sequence:

1. The external switch connects SW to GND to start the system.
2. The microcontroller boots and drives HOLD HIGH.
3. The user opens the external switch.
4. SENS returns HIGH while HOLD keeps the system powered.
5. The microcontroller detects the switch change and performs any required shutdown tasks.
6. When shutdown is complete, the microcontroller drives HOLD LOW.
7. SBK_SP1 disconnects VOUT from the load.

This allows firmware to save data, stop peripherals, or perform other cleanup before removing power.

Using a Momentary Push Button

SBK_SP1 can also be used with a conventional momentary push button.

Connect the external button between SW and GND, or simply use the onboard button.

A button press starts the system and pulls SENS LOW. The microcontroller can then assert HOLD to keep itself powered after the button is released.

Because SENS remains independent of HOLD, the same button can continue to be monitored by the firmware while the system is running.

Applications

Microcontroller platforms

• Arduino
• ESP32
• RP2040
• ATtiny
• STM32

Example applications

• Portable instruments
• Battery-powered sensors
• Educational electronics projects
• Custom embedded devices

Notes

• HOLD is an active-HIGH input and should not exceed VIN.
• SW is an active-LOW input and is activated by connecting it to GND.
• SENS is an active-LOW sense signal and requires an external or MCU internal pull-up.
• The onboard push button and external SW input operate in parallel.
• Do not apply an external positive voltage directly to SW.
• Inductive loads require an external flyback diode or equivalent protection.
• High-capacitance loads may require inrush-current limiting.
• The 2 A rating is the maximum recommended module load; consider wiring, connector, thermal, and application conditions when operating near the maximum current.

Getting Started

This project is fully open-source hardware. You can:

• Build your own module using the provided KiCad design files.
• Modify the design to suit your application.
• Manufacture your own boards.

Assembled Modules

If you prefer a ready-to-use module, fully assembled SBK_SP1 boards may be available in small batches on demand.

For availability, pricing, or quantity inquiries, contact:

📧 SmartBuildsKits@gmail.com

These modules are intended for hobbyists, educators, prototypes, and small-scale projects. Availability depends on component stock and production capacity.

Related Projects

• SBK_FET1 – N-Channel/P-Channel FET modules
• SBK_RP1 – Reverse Polarity Protection Module
• MémoBot – Educational memory game built using SBK_SP1 and SBK_RP1

Contributing

Suggestions, bug reports, and improvements are welcome.

To report a problem or suggest an improvement, open an Issue. Pull Requests are also welcome for corrections, documentation improvements, and design changes that make the project easier to understand or build.

Support the Project

If this project is useful for learning, teaching, or prototyping, you can support its continued development.

Donations help fund prototype hardware, documentation, educational resources, and future open-source projects.

❤️ Support the project through PayPal

Thank you for supporting open-source educational hardware.

License

This project is released as open-source hardware under the CERN Open Hardware Licence Version 2 - Permissive (CERN-OHL-P v2).

You are free to study, modify, manufacture, and distribute this design, provided the terms of the license are respected.

See the LICENSE file for the full license text.

Design Files

This project was designed using KiCad 10.