Pi Power Guard

Safe and reversible power-saving configuration for Raspberry Pi 3B (Model 1.2) on Raspberry Pi OS Bookworm (Debian 12).

This project includes:

• A systemd service that disables USB (and Ethernet) when a flag file is present
• Config.txt modifications to disable HDMI output, Bluetooth, and other unused subsystems
• Full recovery possible by editing files on the SD card from another machine

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🔧 What It Does

1. USB + Ethernet Power Control via Systemd

• Disables USB ports (and Ethernet, which is USB-based on the Pi 3B)
• Only runs if a flag file /boot/firmware/disable_usb exists
• If disabling fails, it creates a debug marker (usb_disable_failed) in the user’s home directory

2. Static Power Savings via config.txt

Disables firmware-based subsystems:

• HDMI output
• Onboard Bluetooth
• Onboard audio (optional)
• Camera firmware loading (optional)

All changes are safe to undo by editing the SD card offline.

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📁 Files

File	Purpose
disable-usb.service	systemd unit that runs once at boot
disable-usb-if-flagged.sh	Script that checks for the flag and disables USB
README.md	This documentation

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🛠️ Setup Instructions

1. Install the systemd USB control service

sudo cp disable-usb.service /etc/systemd/system/
sudo cp disable-usb-if-flagged.sh /usr/local/sbin/
sudo chmod +x /usr/local/sbin/disable-usb-if-flagged.sh
sudo systemctl daemon-reload
sudo systemctl enable disable-usb.service