Decades old TV gets sleep function thanks to 7400 family of chips

[Viktor] dredged up a hack he pulled off years ago. His grandfather likes to end the day in front of the TV, but he falls asleep soon after sitting down. Rather than tick away the electricity meter all night, [Viktor] built an automatic shutoff which is akin to a modern TV’s sleep feature.

At the time microcontrollers were not as easy to source as they are now. So [Viktor] used a circuit based on the 7400 family of logic chips. It uses a multivibrator to feed some binary counter chips. These are used to divide the oscillations to establish the desired timing. He tuned the system to be about 15 minutes, but that can be adjusted using a potentiometer built into the multivibrator. When time is about the run out an LED next to the TV comes on. This way if [Viktor's] grandfather is still awake he can press a button next to his chair to reset the counter. But if he’s already snoozing the counter will eventually switch off the television.

Comments

  1. Bogdan says:

    the power supply part of the eagle schematic is incorrect….(it’s right on the hand drawn schematic).

    It does seem like a nice piece of design. my choice in making this would have been a dual opamp + RC circuit. 1 opamp triggers the warning the other the shutdown. but i don’t know which could have been better in terms of cost in the ’80s.

  2. waf says:

    why bother with logic gates and stuff when you can get an AVR uC for about 5$

  3. metai says:

    You know, I have been wondering for years why modern TVs have everything from media players to web browsers and whatnot, but a simple idea like a “dead man’s button” with an on-screen notice that the TV is going to turn off in a few minutes if no key is pressed on the remote apparantly poses too much of a technical problem.

    (If some manufacturer implemented that, I apologize. I still have to encounter one.)

    • Spork says:

      So I can be interrupted in the middle of my 2-hour program by a notice that tells me I’m not changing the channel often enough?

      • dude says:

        He means a sleep timer with a pre-shutdown warning. I have yet to encounter a TV with that either and I think it would be a good idea. I hate waking up in front of my tv at 5 am wondering what happened and seeing an XBMC screen burned in. That is another part of the problem. A sleep timer for your cable box or in my case my HTPC. Does anyone know of a way to implement a sleep timer like this on my windows based XBMC HTPC? my TV automatically shuts down if no signal for 2 minutes so finding a PC solution would be perfect for me.

    • hardcorefs says:

      24 hour or TV test cards TV sunk most of these designs.

      You don’t need to get complex , just look for the “flyback” or “door step” pulse if it’s not there then neither is the picture!!

    • zarnochwf1 says:

      I know Sanyo flat screens have that as an option in the settings menu, you can specify how many hours you want it to wait without remote input before doing a power off.

      It’s buried in the “eco mode” settings I think.

    • Kevin says:

      Philips have a four hour inactivity timer on some (maybe all) of their TV:s.

    • dr_wummi says:

      my BenQ MP730 also has this option for 30 min / 1 hour and 2 hours.

      my old LG TV also has a sleep feature.
      there are newer TVs that don’t have this functionality? im baffled

  4. PTFarnsworth says:

    Use a push button to charge a capacitor on the gate of a cheap mosfet. The cap drains, then shuts off the mosfet which kills the relay. See page 17 of Forrest Mims Circuit Scrapbook on Google. Super simple, adjustable from minutes to hours.

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