Larc wrote:
On Mon, 19 Jun 2017 13:07:30 -0400, Paul wrote:

| Larc wrote:
| This is a bit off topic, but I have a question that should benefit from answers here.
|
| My main computer is usually turned on shortly after I get up in the morning and not
| shut down until just before I go to bed at night. I've also been turning off the
| monitor, but am wondering if it would be better -- or at least no worse -- to just
| leave it on. If too much of Windows loads before I switch it on, some visual
| settings are affected. I'd like to avoid chances of that by leaving it on. Specs
| show my monitor draws only 0.5W in sleep mode, which is only 0.2W more than it draws
| when turned off. Are there any significant negative factors in leaving it on?
|
| Larc
|
| You can set the time constant on screen blanking, in the
| Power control panel, and that will blank the screen after
| 20 minutes or whatever. If you move the mouse, it lights up
| again.
|
| That leaves the power running on the monitor, but as you say,
| it only draws half a watt. On the old CRT monitors, doing this
| (surprisingly) saves no power at all. My old monitor would
| still draw 200W with a blank screen. But LCD monitors are
| pretty good.
|
| Both LEDs and CFL tubes in computer monitors, have a limited
| life. You can pretend for the sake of "orders of magnitude",
| that the failure time is the same. The lifetime of the part
| that lights up, might be 20K to 25K hours, and blanking it
| will pay off a bit. On an LCD monitor with CFL tubes, usually
| the inverter fails before the CFL tubes do, and if it
| doesn't light up before it hits 20K hours, that's probably
| a defective inverter.
|
| It doesn't really matter whether it's in the 0.5W state
| or 0 watt state. If you do flip a switch to "isolate" the monitor
| from the mains, then there is less risk a lightning transient
| could come up the power cable and get the monitor. But I don't
| worry about stuff like that. If bad weather is forecast, I might
| isolate the computer room for safety, and disconnect the ADSL
| phone line. But induced lightning effects can still blow up
| the LAN ports if I do that, so that's still not a guarantee.
|
| Paul

Thanks, Paul. A big plus for LCD over CRT is the power factor. My 27" 4K monitor
draws less than 30W in full operation. I already have things set to put the monitor
in sleep mode after 45 minutes of inactivity. But I'm more concerned with turning
the monitor off or leaving it in sleep mode when the computer is shut down. I'm
thinking from your reply that it really makes no difference as far as the monitor is
concerned.

Larc

The screen can be blanked by dropping the VSYNC and HSYNC.

And when the computer is off, the same thing happens anyway.

*******

The various cabling standards to the monitor, implement the controls
slightly differently.

On VGA, it's RGBHV. Three colors, horizontal sync, vertical sync.

On DVI, it's RGB and a Clock pair. The Clock pair is multiplied
up, to make a pixel clock, and that eliminates the need to drive
a pixel rate clock down the cable. Because it's just RGB, the
sync needs to be "embedded" in the signal some how.

On PDF page 10, you can see the inputs.

https://media.digikey.com/pdf/Data%2...s/TDA9983B.pdf

HSYNC Horizontal sync pulse
VSYNC Vertical sync pulse
DE Data Enable

B
G
R

The wires on the cable, carry 8B10B encoded data. 10 bits are
transmitted, for an 8 bit color value. The "excess" of information,
allows out-of-band signaling. For example, if a data byte is
sent, there is nothing special about that. But if a "JK" symbol
is sent instead, it can have a special meaning, like "turn on
the Data Enable" or "turn off the Data Enable".

Even audio can be multiplexed into the stream on each gun.

My problem is, finding a diagram with the exact details.

In any case, the concept remains the same. If, at the computer
end, the HSYNC and VSYNC are removed, the monitor end interprets
that as "I should go to sleep now". Because that's what multisync
monitors do.

The DE signal, can be derived from HSYNC and VSYNC. If you didn't
have a DE, you could make one from the info on HSYNC and VSYNC. For
any pixels that are supposed to be visible on the screen, DE is
logic one. For any pixels that are not visible (i.e. time wise,
under the bezel), the DE value is zero.

So when those signals go quiet, the monitor goes to sleep.

If, on the other hand, you pull the cable entirely from the
monitor, the monitor has impedance sensing amongst other
things, and the OSD will report "no signal" or "cable disconnected"
and the OSD may move around the screen to prevent burn-in. I don't
know if my monitor will eventually go to sleep when the
cable falls off or not :-)

My older monitor is a "better sleeper". It shows an OSD
indication for only a few seconds, and then it just goes
black. The newer monitor is a bit of a show-off. But that's
what happens when you only pay $100 for a monitor.

Paul