Putting a monitor to sleep when no video signal - Page 1
Forum section: electronics / general

author: soldar
author_rank: Super Contributor
timestamp: February 05, 2024, 08:44:57 pm
content: I have two 22" Philips 22PFL2807H TV/monitors. They are primarily supposed to be TV receivers but I use them mainly as FHD computer monitors. One I use with VGA and the other with HDMI.The problem is that when the computer goes to sleep after no activity, I expect a monitor to go to sleep when it receives no video input but it does not do that, instead it just displays "No signal from PC" and I have to turn it off manually.I do not imagine any easy solution that would turn off the monitor when the computer sends no video signal. And any possible solution cannot involve just cutting the power because when it comes back the monitor goes to standby mode and has to be turned on anyway.To make matters worse the monitor has no easily accessible buttons so it would have to be turned on and off using IR remote.So I am thinking if there is aneasy way to(1)detect video (or perhaps I could detect mouse/kb activity)And then have a timer that would(2)send IR code to monitor to turn it off.Initially, to me, it sounds like too complicated to be worth the effort. It might be easier to just live with it and turn them off with the remote, which is what I do. But sometimes I forget.

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2024, 09:01:39 pm
content: The cleanest solution would be to make a simple USB device that implements low power mode. When the OS goes to sleep, it would send the device into low power mode, which in turn would activate the IR remote.It is not a huge project, but still a project.

author: soldar
author_rank: Super Contributor
timestamp: February 05, 2024, 09:57:08 pm
content: Quote from: ataradov on February 05, 2024, 09:01:39 pmI had not thought of that but after thinking about it I do not think it would do what I need because my computer is not really "going to sleep" but rather just turns off the video to the screen after a programmed amount of time. It was a good idea though.If there was a way to enable or disable a USB device when the video was turned off I think that would work but I think the only practical way to detect when video is off would be via software and that is way over my head.In VGA I believe the sync signal is dead when there is no video and that would not be too difficult to detect but it would require tapping into the vga cable. I think a high impedance tap into the V_Sync wire would work to detect no video state. The next part would be to simulate the IR pulses or to physically press the remote control button.I don't understand why or how Philips would make a monitor that would not go to sleep on its own.

author: EPAIII
author_rank: Super Contributor
timestamp: February 07, 2024, 09:59:45 am
content: With VGA, video detection is fairly simple. The sync signals are available on the VGA connector and you can use a CMOS inverting buffer with feedback to establish an amplifier with 5X - 10X gain to bring them up to logic levels. The high impedance of the CMOS chip will not degrade the sync signal(s). Then a pulse detector and you have it. Dare I suggest a 555?HDMI, being digital, is a bigger challenge. But a quick search shows HDMI to VGA converters are available a dirt cheap prices. You don't need super quality for video detection, just a way to access that sync signal mentioned above.If you need to go the IR remote way, there are universal IR remote transmitters that can learn the codes needed for any device. Again, they are dirt cheap. But a simple power relay would probably be OK to turn them off and it appears you are turning them back on again manually anyway.

author: ebastler
author_rank: Super Contributor
timestamp: February 07, 2024, 10:14:16 am
content: Most TVs have a "auto-off timeout" feature. It does not do quite what you need -- just switches the TV off if no button has been pressed (or remote control command received) for a time you can set.If you just want to ensure that the monitor does not run overnight or even over the weekend, simply setting a long timeout of several hours might be good enough. Or you could flip the remote-control scheme around: Set a relatively short auto-off timeout, and let your computer send "keep-alive" IR commands regularly via a background task. Or build a microcontroller gadget which monitors activity of an external keyboard or mouse and sends IR commands to the monitor.

author: PlainName
author_rank: Super Contributor
timestamp: February 07, 2024, 10:36:51 am
content: Minor thing to watch out for with HDMI (and other digital) is if the monitor is off when the PC wakes up it make think it's missing, or can't determine the resolution, and change your video settings. I once sent a Samsung monitor back because it took too long to wake up from sleep and then cycled between low and high res during wakeup, which confused the hell out of the PC and screwed up the desktop - icons reordering, etc.

author: Psi
author_rank: Super Contributor
timestamp: February 07, 2024, 10:51:17 am
content: Its possible the TV has a service menu triggered by some special key combo, and that in that menu are options for this feature.See if you can find a service manual for it.

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2024, 10:57:08 am
content: HDMI-CEC allows you to turn on/off a TV remotely. If you can find a way to have both on HDMI, then you might be able to send CEC commands to the monitors.

author: eutectique
author_rank: Frequent Contributor
timestamp: February 07, 2024, 11:00:40 am
content: User Manual, page 10:Auto TV OffYou can set the timeout value of auto off feature. When the timeout value is reached and the Tv is not operated for selected time, the TV will go off.Is it what you are after?

author: ebastler
author_rank: Super Contributor
timestamp: February 07, 2024, 11:03:10 am
content: Quote from: eutectique on February 07, 2024, 11:00:40 amThat's what I described in reply #4, but is probably not quite what the OP is after. "The TV is not operated for a selected time" means that no buttons are pressed and no remote control commands are sent -- both of which don't happen while using the TV as a monitor. But I have described a possible workaround based on this timeout above.

author: eutectique
author_rank: Frequent Contributor
timestamp: February 07, 2024, 11:16:29 am
content: Quote from: ebastler on February 07, 2024, 11:03:10 amCould be, but I only saw such behaviour in STBs, not TVs.Looks like the OP did not try this option yet.

author: ebastler
author_rank: Super Contributor
timestamp: February 07, 2024, 11:20:25 am
content: Quote from: eutectique on February 07, 2024, 11:16:29 amI'm pretty sure that's how it works. The main use case is people falling asleep in front of their TVs -- video feed keeps coming in, but the user does not show any activity.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 12:03:20 pm
content: Thanks all but it seems more complicated and trouble than it is worth. To complicate matters further one is VGA and the other HDMI, one is Windows and the other is Linux.And the monitor does not have a real "standby" state with quick on again but rather it is (soft) off which is called standby but takes a while to get going again.The only thing I can think of might be to disable the screen backlight. It would require opening the monitor but a simple hardware switch or relay could do it. This avoids the unwieldy remote control being in the way. In other words, the monitor stays "on" but the backlight is off so that when it is turned on again the image comes back on instantly. I think the backlight is what consumes most power and turning it off serves the purpose of darkening the screen which is mainly what I want. I might give this option further thought.This reminds me of a similar case I had and have with a microwave oven. All the MWs i have had when you open the door, take out your coffee and then close the door you still have to push a button to start it again so it is not working empty.But I got one which you need to dial the timer back to zero or when you close the door it will start up again. I found that extremely annoying and I was designing a circuit that would require the MW to be restarted manually after opening the door. But time went by and I just got used to turning the timer to zero before opening the door and now I do it reflexively, without thinking. So the circuit I was thinking of turned out to be unnecessary.I think turning the monitor off manually might be the easiest solution but i am going to keep thinking about the backlight.

author: ebastler
author_rank: Super Contributor
timestamp: February 07, 2024, 12:46:32 pm
content: How about setting the TV's internal timeout to, say, 4 hours to make sure it does not stay on forever? If you end up actually spending > 4 hours in front of your computer, the monitor switching off may be a welcome reminder to end that overly long session.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 01:08:02 pm
content: That's not really what I want. What I really want is the normal behavior of going to standby when there is no video signal from the computer.

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2024, 01:11:03 pm
content: You will discover with LED TV backlights if you simply break the circuit that is used to power the LED array, in most cases the LED driver will go into a fault state and power will not resume after the connection is restored. They have a maximum open circuit voltage (as they are constant-current type) but will go to a fault state once this is reached.If you can isolate the 12V/24V to the backlight controller that might work better. I didn't see many of these drivers that reported the fault state back to the TV, so I imagine that would work ok. But many times the backlight driver is built directly into the PSU or main board.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 03:07:53 pm
content: Yes, the reason I thought about this is that i have been dealing with different LED drivers recently. I have a thread in Repair about a large TVhttps://www.eevblog.com/forum/repair/philips-47-tv-47pfh410988-repair/And, also about two or three years back I bought a bunch of LED ceiling fixtures and they have been failing one after another and I had a look at the driver and found they are putting too much current through the LEDs. No wonder they are so bright! One of my pending projects is to install a resistor in parallel with the LED strip so it will shunt some current away.And, yes, I am thinking preferably in terms of disabling the backlight supply, not just disconnecting the LED load.

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2024, 03:42:47 pm
content: Looking quickly at your model it appears to be an OEM Vestel clone (I fixed so many of these when I was a student). They use a BL_ON signal on the pin from the main board to PSU which is just 3.3V CMOS. Modifying that is trivial. There is also a PWM signal, but I'm reasonably sure that it does nothing if BL_ON is low. Schematics for both power and main board are usually available with a bit of searching. Vestel tends to use "17IPS" or "17PW" part number prefix for their power supplies and "17MB" for the main boards.You might also be able to root the operating system pretty easily to control whatever you want, I did that on a UMC TV (Slovakian vendor of many TVs), I upgraded the bootloader to put a logo of my cat on power on, because well, why not?Vestel don't make monitors (AFAIK) but it might be that you can force a HDMI input into PC mode or just control the PWM over Ethernet/USB if the TV has such ports.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 04:00:41 pm
content: Quote from: tom66 on February 07, 2024, 03:42:47 pmThanks. That is very enticing. I am definitely not going to get into the OS because it just is not worth it for me but hijacking the BL_ON signal seems like a very practical way to do it.The only issue is that the monitor is in use and I would rather not mess with it while I need it. I will have to find the right moment to open it up but this line looks promising. And, frankly, I should have thought of it myself because i have seen this signal in other screens.I will see if I can find the schematic. Thanks.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 04:14:38 pm
content: I have found this image of what I think is the PSU. I assume the AC mains power comes in at the top left white connector, The LED power goes out the upper right white connector and the bottom right, black connector takes the power to the main board and receives the disable signal.Edit: I found the schematic and it looks like pin 3 of the connector is the standby signal but I cannot read the labels well.

author: berke
author_rank: Frequent Contributor
timestamp: February 07, 2024, 04:58:04 pm
content: Quote from: ataradov on February 05, 2024, 09:01:39 pmI like this idea. This way, OP won't have to no mess with his TVs, no degrading the video signals and the solution will still work if the TVs are replaced.Is this a desktop PC? There must be a header somewhere that would tell you simply if your PC is in sleeping or not. Maybe a status LED. I'd personally tap that signal and some 5V and run it to an AVR connected to an IR diode. Worse case a current probe placed somewhere could do the trick.

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2024, 05:39:27 pm
content: The relevant signal will be BKL_ON/OFF, pin 5.You will not want to drive the STBY signal. Main board will expect rails to be available; if you remove the power signal it will either go back into standby state, or into the infamous flashing LED state that Vestel sets do (indicating "some" kind of fault, but never so kind to tell you WHAT that fault is...)Be aware the TV will still be driving the panel in this state, so I expect somewhere around 10 watts power consumption in the pseudo-sleep state.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 07:22:07 pm
content: Quote from: tom66 on February 07, 2024, 05:39:27 pmOh, Ok, thanks. So that signal is coming to the PSU board from the main board so if I force it low by shorting C25 the backlight turns off. In other words, I would short it to gnd after the R42 2k2 resistor and not at the connector. Please confirm this is correct. Since I expect these components to be SMD on the lower side I might have a little trouble finding them. It seems quite easy to implement this part of disabling the backlight. The next part will be deciding how to control this and I might look at the video signal, the mouse signal, etc.Another question. In the schematics I notice items marked SXX (S24, S25, etc) which look like jumpers but in some places they make no sense to me as jumpers. Can you explain this? What am I missing?

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 08:22:34 pm
content: One of the computers has a PS2 mouse and keyboard. This protocol holds the data and clock lines at +5V when at rest and pulses down when communicating the connector also has +5V Vcc and gnd. So it should not be difficult to insert inline a circuit that will detect any communication and after a period blank the screen. As long as there is data on the line the timer is held back. When data ceases the timer starts counting and at the end of the countdown it disables the backlight.Seems pretty easy.

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2024, 10:14:07 pm
content: Quote from: soldar on February 07, 2024, 07:22:07 pmMain board generates that signal to say it wants backlight on, and power supply turns on backlight. The power supply produces both a standby 5V, which is always on, and a 12V/24V supply. The 12V/24V will be switched on when the TV needs it, primarily the higher voltage supplies are for the LCD panel, speakers, maybe an LNB amplifier if the TV has one, as well as the motherboard's supplies that don't run in standby (USB power for instance).You would probably be okay putting a shorting relay or transistor across C25, which would allow you to pull the voltage down across C25. The resistor there limits the current that will be pulled from the system-on-chip that drives this signal. I would not recommend you drive the signal yourself.Quote from: soldar on February 07, 2024, 07:22:07 pmVestel make cheap televisions (among other products), and like to minimise their R&D and production costs. Consequentially, they design a PCB to accommodate possibly hundreds of options, a bit like the venerable Ford Transit can be ordered in some 1 million configurations. However, the good comparisons end there... Their power supply boards are often designed to accommodate anywhere from a 22" set to a 50" set with a few added capacitors and diodes here or there, but they always tend to be woefully undersized and are prone to failure. They use some truly funky designs. It looks like the 5V rail on your board is derived using an NPN transistor from the 12V rail, rather than an LDO, probably because it saves 1-2 cents. That means if the 5V rail shorts it probably smokes that transistor.The 'Sxxx' stuff you see in the schematic will be for the various options. And they never give you a schematic that covers your exact model. Which can be a headache. But, at least you can get the schematics. You just have to figure out what to do with those schematics.Edit: misread you. You got it the right way around first time.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2024, 10:36:55 pm
content: Quote from: tom66 on February 07, 2024, 10:14:07 pmThat's what I said. We are in agreement. I think you misread or misunderstood.OK, at this point I think I will begin by fitting a 5 volt relay to short that signal to ground. that way the activation is completely isolated. Once that is tested and working I will design a circuit that detects mouse activity and activates the relay after a certain time of no activity and keeps it activated until it detects furter activity.It can be an extremely simple circuit except for the timer which will require some kind of counter because it needs to be anywhere between 10 to 30 minutes. I can do it with a 555 and a counter. It does not need any kind of precision.Come to think about it, the monitor backlight should come on when the monitor is first turned on, without need for mouse activity. Or maybe not? i need to think about this.

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2024, 10:48:48 pm
content: Yes, I misread you. Good luck with the hack.

author: soldar
author_rank: Super Contributor
timestamp: February 11, 2024, 01:01:43 pm
content: OK, I took out the PSU board and had a look. After some examination I found the components I was looking for. The resistor marked on the schematic as 2K2 was actually 6K8 .The resistor is located near the connector while the capacitor is located close to the IC and there is a "long" track between them which, conveniently for me, half way along has a pad where I could solder a thin cable. I soldered a cable there and another to ground and drilled a small hole in the plastic back housing so I could take them outside.After closing up the monitor and testing it the system does work; it blanks the screen when I short those wires.When the monitor is on it uses 25W. When I blank the screen it goes down to about 12W, so half. (I am using one of those cheap watt meters that plugs in so I do not know how precise it might be with rectifier-capacitor loads.)I am not sure how much effort I should invest into saving 12W although it is not only that but also that I just like the screen to go dark after a while.Maybe I can start out just with a countdown timer and reset it manually every once in a whileI need to think about this.ETA: The more I think about this the more I think it just does not make sense that a modern monitor would not go to standby. I am thinking that maybe the "No signal from PC" message might last for a long time but not forever. I am going to test some more. Leave it overnight and see.