TV Peripherals Power-Off Delay Relay Circuit (no 555)

Discussion in 'The Projects Forum' started by ElectricGoat, May 19, 2016.

  1. ElectricGoat

    Thread Starter New Member

    May 19, 2016
    6
    0
    Hello there! This is my first time publicly asking for assistance with an electronic project of mine since I usually find all the answers I need somewhere online. However, this circuit has tested me past the point of breaking and I'm out of my depth (which is sad considering how simple the circuit is).

    I am building a simple Power-Off delay circuit for the extension cable connected to all my TV's peripherals (not the TV itself). The USB port of my TV only receives power when the TV is turned on, that's where I started. I wanted my circuit to switch a relay powering the extension cord connected to all of my equipment (PS4, Xbox, Speakers, ChromeCast). I found this helpful diagram online, but it relies on the power source remaining present after the switch is opened. I then thought of using the power of a USB Wall Wart to temporarily power the circuit (and extension cord) for around 10 minutes after the TV's USB lost power.
    After countless different designs and much trial and error I thought I had a circuit that would do the job, but when I put it all together (and tested it again to make sure all was well) and plugged it all in, it didn't work; the diodes got really hot so I unplugged everything. I would really prefer not to have to use a 555 timer for this project, but we'll see. I've seen countless other projects that use a single power supply to run the circuit for a short time after a switch is opened, but I haven't seen one that encompasses the use of 2 power supplies (one to first engage the relay and the second to keep it on for 10 minutes after the first power supply is gone).
    I understand there are products I can buy online that use extension cords with the ability to turn off connected devices when the control device turns off, but I wanted to build in a delay timer to avoid having the TV accidentally turn off and kill the power to the console when I'm playing a game.

    I don't have any nice circuit design software, so I substituted an 8 pin IC for the relay I am using. This is the relay I bought:
    http://www.ebay.com/itm/5V-Two-2-Ch...509345?hash=item2a26055221:g:aVcAAOSw0e9UvczK
    In my diagram pin 1 is Vcc, pin 2 is the control (In 1) and pin 4 is GND. I'm using very cheap transistors I got on ebay, and same with the diodes. After many test it almost seems as if the resistor has no influence on the delay of the circuit power-off: it's primarily based on the capacitor's value. The 47uF capacitor I'm using delays the power-off by around 13 minutes.

    Could it be I have made the circuit to "simple" and there is not enough resistance to reduce the current drawn from the TV and therefor the diodes overheat? I'm confident my soldering is fine since my tests of the circuit with my arduino were fine.

    Again, I'm not very experienced with electronics, I just have a working knowledge of very basis properties of components. I would really appreciate some assistance or advice on how to proceed. Thank you so much.

    AknSF_ElectricGoat.gif

    relay delay_ElectricGoat.gif
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    If the circuit is constructed exactly as described and has no faulty components then there is no way that D1 can overheat, yet you say the diodeS got hot. I would suggest putting another diode in the 5V feed from the wall wart to prevent the TV USB from back-driving it when the TV is switched on and the relay has not yet operated.

    BTW on the timing being little changed by the resistor value - the resistor will change the time constant but it will also change the switching threshold and these two effects will to some extent cancel each other.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    If D1 is overheating, there is an assembly problem. If D2 is overheating, remove it from the circuit and measure both the USB and wall wart output voltages. You might have to add a 3rd diode in series with the wall wart output. Also, what is the part number of the diodes?

    I strongly approve of the no-555 attitude. Separate from that, 10 minutes is a long time for any R-C timer to be accurate, and your transistors will turn off very slowly, increasing their heat dissipation. What is the relay coil current at 5 V?

    ak
     
    Last edited: May 20, 2016
  4. ElectricGoat

    Thread Starter New Member

    May 19, 2016
    6
    0
    Thank you two for you input.

    I admit, the two diodes were so close together I may have misjudged the temperature of D1 considering that region of the board was so hot I took my finger away immediately.

    I will be adding a diode for the wall wart, thanks for the idea, that may be the problem considering when I turn on the TV (and thus power to the USB) the relay doesn't switch at all. In fact, the TV didn't seem to happy with the whole thing: it went to a black screen as opposed to the usual "No input" message.

    Here is a link to the diodes I purchased:
    http://www.ebay.com/itm/271868712491?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
    Additionally, I don't really need an accurate-to-the-second delay so much as a delay long enough for me to get the TV back on again should I turn it off and forget that I had peripherals turned on still.
    I haven't measured the current through the relay at the 5V, I'll look into that.

    Thanks again for your input, I'll get back with an update on the project soon.
     
  5. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,889
    375
    Those diodes need well in excess of 1A to get very hot and there shouldn't be anything like that anywhere in your circuit so something is wrong.
    Double check that everything is connected as per diagram and that there are no short circuits.
    One other possibility is the 47uF capacitor - I would expect that to be a polar electrolytic and hence needs to be the right way round. If is fitted backwards then it will be damaged and lots of current will flow through D1
     
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,033
    1,625
    Why would your TV be turning off by accident while you are doing something with it and then why do you want stuff to stay on for 10 minutes after you shut the TV off unless you manually turn it off instead of going off automatically with it? o_O

    FWIW I have a similar setup where one of the USB ports on my TV powers a tiny 5-volt relay inside my home theater system (Turns main power control systems on and off) to turn everything on and off when the TV is switched on and off.

    No delay timers needed here.
     
  7. ElectricGoat

    Thread Starter New Member

    May 19, 2016
    6
    0
    I'll triple check everything to make sure Albert, and I'm confident my capacitor is oriented correctly, thanks.

    As for why I'm setting a delay tcm, it's mostly a redundancy for if I leave the TV alone and someone else in my house turns it off before I get back while I'm playing a game on my PlayStation. And 'cause I like challenging myself to learning new circuit stuff. I originally had my circuit set up the same way as yours: with no delay set to the relay controlling power to surround sound system.
     
  8. dannyf

    Well-Known Member

    Sep 13, 2015
    1,771
    358
    I have a hard time understanding what you are attempting to do - maybe a shorter and more concise description will work better.

    just wanted to point out that those two circuits are fundamentally different.

    As to your diodes overheating, well it depends on how they are wired and what kind of diodes they are.
     
  9. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,033
    1,625
    So what's wrong with turning the sound system off when it not being used even if it's only for a few minutes? If yours was set up like mine then you only had one button to push to turn the whole system on and off. o_O

    Is the thing Vacuum tube based?

    I just don't follow the logic and reasoning behind adding the long delay off function for the sound system half of things.
     
  10. ElectricGoat

    Thread Starter New Member

    May 19, 2016
    6
    0
    Tcm, I have my circuit control a whole power strip, it's just easier to plug my whole entertainment center (PS4 included) into the strip. I'm not trying to win any awards for perfect individual circuits for each device connected... Don't worry about how I'd prefer to set it up, I'm just looking for input on getting the circuit I have to work. I should have time tomorrow to re-solder it and see if the missing diode was the problem.
     
Loading...