Python scripts and related instructions for for Timer-Relay project.

timer-relay.md

Server (Raspberry Pi Zero)

First, we install gpiozero, if we don't already have it.

sudo apt-get update

sudo apt-get install python3-gpiozero

Next we create the file relay-trigger.py with the follwoing contents:

from gpiozero import Button
from signal import pause
from time import sleep
import socket
import subprocess

DEST_PORT = 17473
DEST_IP = "255.255.255.255"

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)

def doShutdown():
  print("GPIO Change Detected")
  for i in range(3):
    sock.sendto(b'\x01\x01', (DEST_IP, DEST_PORT))
    sleep(0.5)
  subprocess.Popen(['sudo', 'shutdown', '-h', 'now'])

# GPIO where relay is connected
button = Button(21)

button.when_released = doShutdown

pause()

As written, the script detects GPIO 21 and proceeds to send out three sequential UDP packets telling other computer on the network to initiate shutdown.

Now we create a systemd script to automatically launch this program at system startup. Create the file /lib/systemd/system/relay-trigger.service with the following contents:

[Unit]
Description=Relay trigger upon GPIO 2
After=network-online.target

[Service]
ExecStart=/usr/bin/python3 /home/pi/relay-trigger.py

[Install]
WantedBy=network-online.target

Next, we ensure systemd is aware of our new service:

sudo systemctl daemon-reload

Next, we enable the new service:

sudo systemctl enable relay-trigger.service

Finally, we reboot the Raspberry Pi.

sudo reboot

Once reboot completes, we can check if our new services started up:

sudo systemctl | grep relay

Clients

The client can be installed on any Linux or Windows based system. This specific example will focus on a Windows use case.

Create a file titled cliente.py with the following contents:

import subprocess
import socket
import platform

UDP_PORT = 17473

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

sock.bind(('',UDP_PORT))

sysname = platform.system()

while True:
    data, addr = sock.recvfrom(1024)
    if data == b'\x01\x01':
        if sysname == 'Windows':
          subprocess.run(["shutdown", "/p", "/f"])
        elif sysname == 'Linux':
          subprocess.Popen(['sudo', 'shutdown', '-h', 'now'])

Create a shortcut to this file in the Windows startup folder, replacing USERNAME with the actual username of the active user in Windows:

C:\Users\USERNAME\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup

Before restarting Windows, make sure Python 3.0 or newer is installed.