How to check if the monitor connected to the PC is turned on?

Question

System administration

Hello
Let me explain the situation: we have a network of miniPCs on Raspberry Pi, which are scattered around the city, all connected in a VPN network. There are some devices on Windows 7. It often happens that users specifically turn off the monitor, and the device is idling. The monitors are mostly connected with a regular VGA D-SUB cable, the Raspberry uses an HDMI to D-SUB adapter. Colleagues tell me if there is a way to check whether the monitor is connected to the computer and whether it is turned on.

Answer 1

It is forbidden. The VGA interface does not provide such functionality in principle.
The only thing that has changed in recent years is 9,11,12 contacts - they changed their purpose.
The 9th is now the beep for EDDC, 11.12 is the line date for reading display parameters.
As an option, you can try to cut off the 9th output and try to read the display parameters, when it is turned off it will not be possible to do this, but to be honest, it’s nonsense, it’s easier to screw the current sensor to the raspberry and attach it to the monitor’s power wire :)

Answer 2

For Linux, there is xrandr
You can make a script to bypass machines and check which monitor is connected and how

Answer 3

The case of the monitor is disassembled, the panel of buttons breaks out, in parallel, the raspberry is powered from the power supply of the monitor +, if possible, is thrust into the inside of the case.
Conclusion: You cannot turn off the monitor without turning off the raspberry, you can monitor the raspberry online.
It’s more difficult on a PC, VGA can’t give the status of the monitor, again, if you just kill the button or output which trigger to usb