வீட்டுல கரண்ட்டு போச்சுன்னா யாரு எனக்கு சொல்லுவா?

Who will let me know if there is a powercut in my house?

Currentu Pochino!

Monitor your homelab power status with an Arduino! When power cuts out, currentu-pochino detects the state change via a digital input pin and triggers custom on/off actions. Perfect for automated shutdown sequences, logging, notifications, or recovery workflows!

Overview

This project uses components I had lying around. It uses an Arduino Nano (or compatible board) connected via USB to monitor a digital input pin (for example, from a relay sensing AC mains, or a simple 5V output from a wall adapter!). When the power state changes, the Arduino sends ON/OFF messages over serial, and a systemd service (a python script) running on your Linux machine executes corresponding shell scripts. [Sorry Windows/Mac users! You need to do your own work adapting this to your OS.]

Features (of the scripts on this repo):

• Automatic USB device detection and stable /dev/by-id path setup
• Systemd service integration for automatic startup
• Configurable actions via shell scripts defined by you (on.sh, off.sh)
• Simple serial protocol: ON, OFF, or HI (init message)

Hardware

Arduino Sketch (nano.ino)

• Sense Pin: Digital pin 6 (D6) – connects to your power sense circuit
• LED Indicator: Built-in LED (pin 13) – blinks on startup, shows power state
• Baud Rate: 115200
• Debounce: 50 ms (firmware debounce)

Upload nano.ino to your Arduino board beforehand using the Arduino IDE or avrdude!

Circuit of my setup

I have an old Samsung charger which I use to power the input pin. If power goes out, the charger loses power and stops powering the input pin, which makes the Arduino inform the serial port about the loss of power.

Though as I have observed, it practically does not power down instantly! This is due to there being charged capacitors in the charger's internal circuitry (which I have no reference of). It took around 30 seconds to discharge into a 1kohm resistor, to the point that the voltage becomes less than the ATmega328P's Input HIGH level (VIH < 0.6Vcc or approximately 3V), which is sufficient for my use case because I have a UPS. For faster power dissipation, I'd have to use a smaller resistance, but all the resistors I have are rated for 0.25W power dissipation so I'd have to split the small resistance across multiple resistors.

The circuit's schematic on Tinkercad:

KiCad schematic coming soon! (do you really want it?)

Installation

Prerequisites

• Linux system (tested on Debian/Ubuntu, should work on any distro that has systemd and python support)
• Arduino Nano or compatible board with USB-to-serial adapter (onboard USB is fine)
• Python 3 with pyserial installed (python3-serial on apt, python-pyserial on ArchLinux extra repo)
• systemd for service management
• Root access (to install as service - the service itself runs as your user. You can manually install it completely without root access!)

Step 1: Prepare Your Scripts

Clone the repository:

git clone https://github.com/ilamparithi-in/currentu-pochino
cd currentu-pochino/src

and create on.sh and off.sh in the repo directory:

on.sh – runs when Arduino detects power ON:

#!/bin/bash
# Example: Start services, log event, send notification
logger "Power restored on homelab"
# systemctl start myservice
# curl -X POST http://notifier/alert?status=online

off.sh – runs when Arduino detects power OFF:

#!/bin/bash
# Example: Graceful shutdown or logging
logger "Power lost on homelab; initiating safe shutdown"
systemctl poweroff  # or: shutdown -h +5  for delayed shutdown

Alternatively, you can edit the python listener script to modify the actions performed, they do not need to be a shell script!

Step 2: Upload Firmware to Arduino

1. Open nano.ino in the Arduino IDE
2. Select your board (Arduino Nano) and COM port
3. Click Upload
4. Wait for the upload to complete; you should see the startup chime!

Step 3: Clone the repo and Run Installation Script

# current working directory: currentu-pochino/
sudo ./setup.sh

The script will:

1. Auto-detect the Arduino (requires manual intervention)
2. Install the listener – Copies pochino_listener.py to /usr/local/bin/
3. Install action scripts – Copies on.sh and off.sh to /usr/local/lib/currentu-pochino/
4. Install systemd service – Configures and enables the systemd unit with auto-detected device paths
5. Start the service – Enables auto-start on boot and starts it immediately

You can override paths and provide the serial path directly to skip auto-detection:

sudo ./setup.sh -l custom_listener.py \
    -o /path/to/on.sh -f /path/to/off.sh \
    -d /dev/serial/by-id/usb-1a86_USB_Serial-if00-port0

Options:

• -s <service_file> – Custom systemd unit file (default: currentu-pochino.service)
• -l <listener_file> – Custom Python listener (default: pochino_listener.py)
• -o <on_script> – Custom on-action script (default: on.sh)
• -f <off_script> – Custom off-action script (default: off.sh)
• -d <serial_path> – Serial device path (e.g., /dev/serial/by-id/usb-1a86_...); if omitted, auto-detected
• -h – Show usage

NOTE

Using /dev/ttyUSB0 or /dev/ttyACM0 as serial path is not recommended as there may be other serial devices (another arduino you may have connected for some reason) that can take the place of your sensing device. Use the /dev/serial/by-id/... path instead!

Customization

Modifying the Action Scripts

Do not edit /usr/local/lib/currentu-pochino/on.sh and /usr/local/lib/currentu-pochino/off.sh directly!

In the event of a power loss while you have the device connected and the listener running, an improperly edited action script might cause damage to your system! (depending on the commands you have used)

Please edit the scripts separately and run the install script (or copy them manually using the install command) again!

Adjusting Arduino Debounce

Edit nano.ino line 3:

const unsigned long DEBOUNCE = 50;  // milliseconds

Increase if you see spurious ON/OFF transitions; decrease if response feels sluggish. Re-upload after changes.

Changing the Sense Pin

Edit nano.ino line 1:

const uint8_t SENSE_PIN = 6;  // Change to your pin

Re-upload to the Arduino.

Troubleshooting

Arduino not detected during setup

• Ensure the Arduino is connected via USB
• Check permissions: ls -la /dev/serial/by-id/
• Verify USB driver: lsusb | grep -i "nano\|1a86"
• Try manually specifying the path: sudo ./setup.sh -d /dev/ttyUSB0

Service fails to start

Check logs:

sudo journalctl -u currentu-pochino.service -n 100

Common issues:

• "Permission denied" – The dialout group or device permissions may be wrong. Verify: groups | grep dialout
• "Module not found: serial" – Install pyserial: sudo apt install python3-serial
• "Device not found" – Arduino unplugged or wrong path; verify with ls -la /dev/serial/by-id/

Arduino keeps sending "HI" on every connection

This is normal. The Arduino resets when the serial port opens (DTR/RTS pulse), running setup() again. You can modify the listener script to not print an initialization message every time it detects one, or you can disable auto-reset; custom actions only trigger on "ON"/"OFF".

To disable auto-reset on your Arduino, add a 100nF capacitor between RST and GND (or search the solution for your own board).

Custom scripts not running

Ensure:

1. Scripts have proper shebang: #!/bin/bash
2. Check logs for errors: sudo journalctl -u currentu-pochino.service

Service Configuration

The systemd unit file (currentu-pochino.service) is installed to /etc/systemd/system/ with:

• User: you!! (if you used the install script, this would've been automatically replaced with your user)
• Group: dialout (for serial port access)
• Auto-restart: On failure, with 15-second delay
• Environment: Passes ARDUINO_SERIAL_PATH to the Python listener

To edit the service manually:

sudo systemctl edit currentu-pochino.service
sudo systemctl daemon-reload
sudo systemctl restart currentu-pochino.service

Uninstallation

Things to remove: The systemd service, the action scripts, the listener script, and finally the unit file from /etc/systemd/system.

sudo systemctl disable currentu-pochino.service
sudo systemctl stop currentu-pochino.service
sudo rm /etc/systemd/system/currentu-pochino.service
sudo rm /usr/local/bin/pochino_listener.py
sudo rm -rf /usr/local/lib/currentu-pochino
sudo systemctl daemon-reload

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