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Thread: Momemtary switch to cut all power to comp

  1. #11
    FLAC PatO's Avatar
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    Quote Originally Posted by Geking
    I would do a diagram, but Alas, I am on the road.
    Drool
    I'll have to admit, I'm having trouble visualising what you're talking about, but since the parts aren't available at my local ratshack, I'll have to order online anyway. So, I'll take the elegant route and pick up a latching relay....
    Thanks for the tip though, another solution to a unique problem. Always fun to think about new ways of doing things.
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  2. #12
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    Quote Originally Posted by Geking
    Yes, a latching relay is deffinatly the best way to go.
    I 'cheated' and used a 4throw double pole 5 v relay. I had the momentary switch on one part of the relay, to close the loop to some batterys to 'jump' the relay. the relay catches, gives 120 to the pc, bios is set to on after power resume, gets its power off of the now powered compy, recharges the batts, and makes the switch go to the motherboard's power switch header.
    I could have done something much more elegant, but it was all I had laying around the house.
    I would do a diagram, but Alas, I am on the road.
    Well, I've searched, and found diagrams. Been to RatShack dozens of times with no luck. Likely it's due to part numbers not matching up and resistances being askew...

    Geking, would you care to describe/diagram your circuit with the 4PDT relay? I have one of those sitting around, and have tried building it myself, but can't figure out how to unlatch it with a second press of the switch. I also have two DPDT relays, if that helps...

    Does anyone else have ideas about how to make a relay latch from a single momentary toggle using the severely limited resources of RatShack? How about a circuit that *actually* works and is in use right now (with parts from the online places)? I think I'm going insane!!!
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  3. #13
    What can I say? I like serial. Curiosity's Avatar
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    PatO, that one in your first post would work. It only takes a pulse to get it started. The only thing you need to do is remove the COM port stuff or just don't enable the UPS in Windows and it will stay on forever. To turn it on and off with each press, you could connect another relay to the remote and contacts go to the power button. Off would work, but not sure about on. It would pulse right as it gives power to the whole thing. Do you know how long the pulse is? If it's over about 1 second it should work great.

  4. #14
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    Yep, I've thought about that circuit, but I don't want to rely on the computer shutdown sequence to turn the thing off. Although, I suppose I could rig up a timer circuit to somehow turn off the main relay... Hmm... At any rate, this momentary latching circuit will compliment that circuit and allow me to use the trunk popper from my remote starter.

    I've been focusing on a 4-relay setup for a while now (attached) . It seems that the relays are only enguaged while the computer is on, so I shouldn't have to worry about burning out coils (much). I've rigged it up with different types of relays (don't have 4 of one type) and haven't had any success. I just bought 4 micro relays, and will give it a shot now. (fingers crossed)
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  5. #15
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    Okay... So it appears that the differences in relay coil resistance was the problem. Using 4 identical relays worked!

    And they all stay off when the circuit is off, so that's a good thing.

    Now, I realize most of you are cringing at my use of relays in this circuit. I am too. In my test of this circuit posted by rubicon, I used a TIP3055 (276-2020) and MPS2222A (276-2009) instead of the suggested 2N3053 transistor. It didn't work. How different can those transistors be? If I compare the specs, I see this:
    3055 (my closest match)
    Vcbo = 70V
    Vceo = 60V?
    Vcex = 60V?
    Vebo = 5V
    Ic = 10A

    3053 (used in the schematic)
    Vcbo = 60V
    Vceo = 40V
    Vcex = 60V
    Vebo = 5V
    Ic = 0.7A
    So, what does this mean? How should I adjust the circuit to account for the differences between the transistors? It is worth noting that there are no other discrepancies in the circuit, I have all of the suggested resistors, diodes, and caps.
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  6. #16
    What can I say? I like serial. Curiosity's Avatar
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    What's the voltage on the output of the transistor? If it's too low, I'd think you need to lower the resistance to the base. Can't somebody smart help here?

    I think I understand what you want to do, and can see a few ideas in my head, but they are a little fuzzy. First, you could have something like this:
    remote AUX >---[relay]===> power button
    That would give you a remote controlled power button. Then, instead of a relay that toggles each time from that input (that would be really bad) use something that goes on and stays on until the power from the PC goes off, which is what the diagram in the 1st post shows. The only problem with that is no timer in case it hangs. Chris31 and I were discussing this in a thread before all hell broke loose, here at the end:
    Idea for your own shutdown controller.
    Only problem is, I don't even know if it works yet but the idea is pretty close.

  7. #17
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    This is my plan. It's a hodgepodge of several threads... Note that the momentary to constant circuit will change based on the results of my questions here...

    The timer circuit is only there as a backup if the the +12 wire from the comp doesn't shut off. And I just noticed that a couple of my diodes are backwards .
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  8. #18
    What can I say? I like serial. Curiosity's Avatar
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    Ah ok, so the momentary to constant toggles on/off to turn the main relay on, and when it goes off, it starts the timer which holds it for another minute or so? That looks good. I'd hate to hit the button twice by accident though, or whatever that could get it in the wrong state. heh. Also, the relay on the COM port isn't needed. It's designed so that every pin can take 25V and any pins can be shorted together, so it can take 12 directly, although it's safer to use a relay in some way I guess, but that's a good thing to know.

  9. #19
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    Quote Originally Posted by Curiosity
    I'd hate to hit the button twice by accident though, or whatever that could get it in the wrong state.
    Good point... I've been racking my brain trying to figure out a solution... Another timer or software to raise a parallel port pin after boot would work, but eh. Too much work for now. I'll just have to remember to not hit the buttons twice, I guess. Perhaps put a red LED on my antenna to let me know that the comp is booting!

    Quote Originally Posted by Curiosity
    Also, the relay on the COM port isn't needed.
    Sweet! Saves me a couple bucks on a relay. However, then that power is going to come directly from the battery. But if I have 25V to play with, it should be fine.

    Edit: It's low power, so I bet I could use a transistor rather than a relay...
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