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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
LCD's suffer from a terrible condition called image persistance. Its similar to burn-in although it is only temporary. It lasts for a day or two.
If I forget to turn off my TV or PS3 and leave for work then the pause screen gets burned into the screen.
My solution is to build a circuit that would interupt the power to the TV. The ideal circuit would be normaly closed and every 6 hours or so would open for a second or so.
Would it be possible to base this around an NE555 and a relay?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
6 hours is a long time for a 555.
Since the controller will probably be mains powered I'd consider (mains frequency) / N, e.g 60 Hz with a 4020 14-bit divider would give 1 cycle about 4.55 hours. You can make the controller disconnect the load(s) and itself.
You could trigger 1/2 of a 556 with the output of the counter, say 1 minute early warning this can enable the other half of the 556 to make an audio tone ..etc. etc. This way you get a warning before the unit disconnects the loads, enough time to press the countdown reset/start button. Wouldn't want to power down in the middle of using the loads.
This would all be easy with a microcontroller (PIC etc.) but requires programming.
This application is good, there must be a latent demand out there. Maybe there are cheap units already available ?
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Use a passive IR motion detector coupled to a short (20-30 min) timer. No motion detected, you are either absent, asleep, or deceased. The timer activates and in 20 minutes if you do not resurrect, the monitor shuts off.
Registered Member #2140
Joined: Tue May 26 2009, 09:16PM
Location:
Posts: 53
Most TV's already have an auto shutoff (mine does, and it's fairly old), but hidden in menus.
If not, you could use a capacitor, a voltage source and a resistor. Calculate a proper resistance for the capacitor and voltage so after x amount of time, the voltage reaches y voltage.
The capacitor is hooked up to a simple comparator circuit, which triggers the relay.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
The external timerbox solution may be an answer, and many options can be used to program the relay. One thing to consider is the overall integrity of what you build. Your TV and the power cord are part of a system supported by a chain of safety tests which are certified by the sticker that allows it to be sold. Your addition then becomes the unknown link, that may sit energized for days or years.
There is another factor, you built it, you know it well. What happens if you no longer are the user? I mention this because time goes by, estates of people highly regarded in a small technical groups get scattered and can cause harm in the wrong hands.
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
Great help! I think that I will probably use the 14 bit divider to solve the issue. I will build multiple units since this will help with a problem I discussed in another thread regarding a heating blanket.
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Image "burn-in"
