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Thread: Creative use of relays - will this work?

  1. #11
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    I really like your idea and I think that I'm going to use it as well.

    Basically yeah, 99% of the time when I lock the doors it means that I want the computer to shut off, and when I unlock the doors I'll want the computer to turn on. That's actually awesome because you usually unlock the doors a good 15-20s before you start the engine, giving the computer that long of a head start to boot, effectively saving you that much waiting time. If you're using STR then the computer will have booted even before you start the engine!

    And it'd be really simple to have the power door locks just issue an ATX power switch pulse (literally just one relay) whenever the doors lock or unlock.

    Add in a "bypass switch" so when you go into a store for a few mintues you can lock/unlock without the relay pulsing, and you've got a very convenient system that's very simple to implement.

    The only worry is that for some reason the computer remains on after the doors lock, and then draining your battery. So you'd still need some sort of protection against that, but that's a pretty simple thing to hook up too. (i.e. have a relay that is normally closed that will fire open for 1second (effectively terminating power to the computer) when the battery voltage drops below a certain level (say 8V). Provided that you don't have the computer set to auto turn on once power is restored, then the computer will stay off. Since this is a failsafe anyway (i.e. it should happen very infrequently) it's OK to just abruptly terminate power to the computer.

    That way you don't even need to do the dual relay and running one off the PSU power route, you only need one relay (and this allows the 5VSB to always work), and STR to be used.

    If you don't want 5VSB to stay on then using your dual relay method would work better.

    Awesome, what a simple idea! Congrats!
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  2. #12
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    Thanks! Actually my failsafe is in the inverter, it shuts down before the voltage is so low that I can't restart the car. It actually happened yesterday, when I was playing around with the system, adjusting sound and doing a bit of programming on the Girder interface (I made it simpler to use - if you now press the 1-4 digit code for a play list (I have all my cd's as play lists sequentially numbered up to about 1600 at the moment) you get asked if you want to play that playlist to the car stereo system, to Kevin's headphones or to Lisa's headphones, something my wife really liked since it's easy to forget to change zone before you punch in a play list number) the inverter shut down. I had to start the car and run it for a few minutes before I could use it again.
    Tor - The MediaSUV

  3. #13
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    So you actually need 3 relays then, 2 for the power and 1 for the ATX switch?
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  4. #14
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    Yes, but as you pointed out, it can be done with diodes instead, then you need two relays, one for the power and one for the ATX. But I'm taking this even further, I'm putting two relays on the car stereo system as well, so it can be powered by either turning on the computer or by the alarm being in the off position (right now it's on the key, and it drives me nuts, but I found out two years ago that it steals a lot more power when it's not on a trigger than when it's on a trigger and the trigger is turned off).
    Tor - The MediaSUV

  5. #15
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    It could be because I'm running on very little sleep, but your last post did not make a helluva lotta sense. What trigger? What is on the key and drives you nuts? What steals a lot more power? huh?
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  6. #16
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    The trigger is the voltage that powers up the sound system (switched power, usually via the ignition switch, but I will put mine via the alarm). And the sound system stole more power when it was turned off just by the button but there still was power connected to the switched input. I have no idea why, but I checked it with an amperemeter, and the difference was significant enough to kill my car a few times when I didn't drive it for 3-4 weeks.
    Tor - The MediaSUV

  7. #17
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    You mean the accessory line And when you say "stole more power with just the button" you mean by leaving the radio connected to the +12V mains all the time, and just turning the radio off by the power button on the radio itself?

    Well 3-4 weeks is a very long time to go without driving a car if you have anything drawing power, even a small 5W drain will kill the battery in a week or two. The radio will definitely take more power when the ACC line is on as opposed to when it is off (when it's off the only thing is powers is the memory and the clock), when it's on it powers a few more things and puts the radio into a "standby" state so that it can be turned on by the electronic power button, so yeah I'm not surprised that it would kill your battery after 3-4 weeks of not driving it.

    So why is it a problem to have the radio powered off of the ignition ACC line, rather than the alarm line? (and by alarm I assume you mean when you deactivate the alarm it will power the radio on?)
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  8. #18
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    You're right, it's a long time. But this is a Chevy Sub that normally can stand still for two months and then fire up perfectly. Normally we use the Mazda MX-3 for local driving, the Chevy is used as an extra car and as the large family car on longer trips. So sometimes it stands still for quite a while, especially in the fall, when we don't visit the cabin.

    And yes, I mean that when the alarm is on, the trigger/accessory/switched power is off.
    Tor - The MediaSUV

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