Scripts to start and stop moonlight systemd service automatically only when the TV is turned on, by connecting the 5V/500mA USB from the TV to Raspberry Pi (3B+) GPIO17 via a 25kΩ/50kΩ voltage divider for a (hopefully) suitable 3.3V signal. Smaller resistors might also work, but this is what I had and it works for me.

moonlight-gpio.py

#!/usr/bin/env python

# This is for the magical gpio button, ignore if you're not going to solder one

import dbus
from gpiozero import Button
from signal import pause

sysbus = dbus.SystemBus()
systemd1 = sysbus.get_object('org.freedesktop.systemd1', '/org/freedesktop/systemd1')
manager = dbus.Interface(systemd1, 'org.freedesktop.systemd1.Manager')

def on():
    print('TV is ON')
    manager.StartUnit('moonlight-qt.service', 'fail')

def off():
    print('TV is OFF')
    manager.StopUnit('moonlight-qt.service', 'fail')

tv = Button(pin=17, pull_up=False, bounce_time=1)
tv.when_activated = on
tv.when_deactivated = off

if tv.is_pressed:
    on()
else:
    off()

pause()

moonlight-gpio.service

# This is for the magical gpio button, ignore if you're not going to solder one

[Unit]
Description=Moonlight GPIO button
After=network.target

[Service]
ExecStart=/home/pi/moonlight-gpio.py
Restart=always
User=root

[Install]
WantedBy=multi-user.target

moonlight-qt.service

# This unit is disabled, but is started on boot by the other one if the TV is on,
# or toggled by the GPIO cable when the tv turns on or off.
# Or you can just enable it by default and ignore the other files.

# QT version on RPi 4B

# I'm using RaspiOS trixie Desktop (2025-12-04-raspios-trixie-arm64.img)
# This setup is used as a 1080p60 HEVC remote screen only, over local ethernet. Latency is around 2f @ 60fps.
# I don't really care about audio or input, but they should work too.
# /boot/firmware/config.txt is all vanilla.
# The desktop part is disabled in raspi-config (boot to console) and probably fiddled with some audio/video settings too.
# These configs have nothing to do with the desktop, but you can try to wing it if you really want to use xorg or wayland.
# I can't recommend running in wayland or xorg, it will have worse performance than eglfs on console.
# Just figure out how to create systemd services and configure this crap over ssh.
# And follow the official installation guide:
# https://github.com/moonlight-stream/moonlight-docs/wiki/Installing-Moonlight-Qt-on-Raspberry-Pi-4

[Unit]
Description=Moonlight QT stream
After=network.target
StartLimitIntervalSec=0
StartLimitBurst=0

[Service]
Environment=QT_SCALE_FACTOR=0.9
Environment=QT_QPA_EGLFS_ALWAYS_SET_MODE=0
Environment=QT_QPA_PLATFORM=eglfs

# Might need to explicitly switch to pipewire in raspi-config too
Environment=SDL_AUDIODRIVER=pipewire

# Force sound to specific device
# Get node name with: pw-dump|grep node.name
# pulsemixer is a good program to change and debug audio outputs over ssh
#Environment=PIPEWIRE_NODE=bluez_output.BC_A0_42_70_07_24.1
Environment=PIPEWIRE_NODE=alsa_output.platform-fef00700.hdmi.hdmi-stereo

# This fixed all my audio crackling issues on Pi4, adds tiny bit of audio latency
# pw-top might be useful for checking errors and current latency
Environment=PIPEWIRE_QUANTUM=960/48000

# You should probably pair and configure other stuff first by running moonlight-qt interactively
ExecStart=moonlight-qt stream --platform minimal --1080 --bitrate 20000 10.0.0.10 Desktop
Restart=always
RestartSec=1
User=pi
StandardOutput=truncate:/tmp/moonlight.log
StandardError=inherit

# You should systemctl disable getty@tty1 when using these two:
PAMName=login
TTYPath=/dev/tty1

[Install]
WantedBy=multi-user.target

moonlight.service

# This unit is disabled, but is started on boot by the other one if the TV is on,
# or toggled by the GPIO cable when the tv turns on or off

# Embedded version on RPi 3B+
# Requires vc4-fkms-v3d in config.txt to work
# This my old bare minimum setup I sometimes used to stream youtube to the kitchen, never paid much attention how well audio etc works
# Latency is probably better but smoothness is worse than the qt version on 4B, but qt really doesn't run on 3B.

[Unit]
Description=Moonlight stream
After=network.target
StartLimitIntervalSec=0
StartLimitBurst=0

[Service]
ExecStart=moonlight stream -1080 -bitrate 20000 -app Desktop 10.0.0.10
Restart=always
RestartSec=1
User=pi
StandardOutput=truncate:/tmp/moonlight.log
StandardError=inherit
# You should systemctl disable getty@tty1 when using these two:
PAMName=login
TTYPath=/dev/tty1

[Install]
WantedBy=multi-user.target

remote.hwdb

# /etc/udev/hwdb.d/99-remote.hwdb

# remap tv remote "ok" to spacebar
# ymmv, copy scancode from: evtest /dev/input/event0
# reload: systemd-hwdb update; udevadm trigger

evdev:name:vc4-hdmi-0:*
 KEYBOARD_KEY_0=space
 

voltage_divider.png