Circuit Madness

[Zuph]

Dunno if this would belong here or not, but to me, this seems Highly Technical. Sorry ahead of time if I screwed up, mods.

Anyway. I want to put a computer into a car. I also want it to turn on and off when the car turns on and off. This isn't a matter of just having the button "on" all the time, and tying it into power because of the ATX spec. I want to make a circuit that will activate a relay on voltage CHANGE, and tie that into some car power line that receives it's voltage according to whether the car is on or off. I want the relay to turn on the computer (like hitting the button would) whenever the voltage changes from on to off, or off to on, turning the PC on when I start the car up, and shutting it down properly (just like the button would) when I turn the car off. I don't have any clue as to how I would make a circuit that would do this. Sorry if I've just wasted your time :-\

 

[CallTheFBI]

If you want to put your computer in your car (don't really know why you want to do this) then what you need is something called an AC inverter. This turns your car's DC into the power you need which is AC. Now the thing is that your computer's power supply requires quite a few watts, so I hope you have a pretty big engine. The AC inverter I have for my car has a maximum load of 450 watts and that is only if it is hooked directly up to my car's battery. If I use the cigarrete lighter adapter it has a maximum of 150 watts.

 

[Zuph]

I don't mean how will the computer get power, I mean how will I trigger the computer to turn on and off with the car, so that it shuts itself down properly. I'm using Mini-ITX stuff, and an LCD, so the power draw shouldn't be over 150 watts. I want to put it in my car for MP3's, DivX, Navigation, and maybe a few SNES games at really long lights

 

[CallTheFBI]

Originally posted by: Zuph
I don't mean how will the computer get power, I mean how will I trigger the computer to turn on and off with the car, so that it shuts itself down properly. I'm using Mini-ITX stuff, and an LCD, so the power draw shouldn't be over 150 watts. I want to put it in my car for MP3's, DivX, Navigation, and maybe a few SNES games at really long lights

For turning it on I would imagine a simple circuit that switches on when the voltage drops would work. You would hook your power supply directly up to your car's battery, when you turn the ignition the voltage drops triggering the switch to turn on. As for shutting down, that's a different problem, wouldn't have a clue how to do that.

 

[Zuph]

Originally posted by: CallTheFBI


For turning it on I would imagine a simple circuit that switches on when the voltage drops would work. You would hook your power supply directly up to your car's battery, when you turn the ignition the voltage drops triggering the switch to turn on. As for shutting down, that's a different problem, wouldn't have a clue how to do that.

Yep, that's the problem

 

[talshiar99]

Most current ATX computers the pushing the off button will tell it to shut the computer down. An ATX switch is just a momentary contact switch. The power supply will have to be tied directly to the battery so that it will have the power to shut down. Now for auto on and off you will have to get into your steering column and put a trigger at the two key positions. The easiest way would be to just put a switch in the car, but you dont want to make it easy do you? Another option would be to check your circutry see what lines have power only when the car is on, attach a sensor to trigger whenever the voltage has at least an 8 volt change which will then trigger the ATX power switch.

 

[chocbrucemousse]

Just wire it to the ignition. Wire the start button for the ATX to the ignition. the ignition works bye using powering the starter...this will turn it on. ummm, then wire a relay to the alternator in such a way that the relay holds open the curcuit when it's running. (hence you will want a relay that is normally closed. I think that should do it. I don't know cars.....but relays r cool =P

 

[NogginBoink]

Originally posted by: Zuph

Originally posted by: CallTheFBI


For turning it on I would imagine a simple circuit that switches on when the voltage drops would work. You would hook your power supply directly up to your car's battery, when you turn the ignition the voltage drops triggering the switch to turn on. As for shutting down, that's a different problem, wouldn't have a clue how to do that.

Yep, that's the problem

Dig around for a wire that's hot when the ignition key is in the 'on' position. You'll find several (the radio power line, for instance, in most cars). Use that to trigger your circuit.

 

[rummyPPG]

Perhaps you should try e mailing panasonic or sony or someone who makes audio devices for cars and see how they handle it (tell them you're doing a student project ;^). I mean the problem is analagous to an in-dash cd player stopping itself from spinning and turning off when the car is shut down. Plus, they have some cool features, like keeping the music on even after the engine is turned off but only until the door opens.

Also, I don't use it much, but UPS devices communicate with the COM port to give information on the power in the system and windows also lets them shut it down, so that might be the "simple" answer you're looking for. If your car computer can shut down in 30 seconds, then all you need is something that will give it power for 1 minute while that something triggers the shut down over the COM port.

In that way you'd have the car battery plugged into your "UPS" which plugs into your computer. Then when the car shuts down, make sure power to the "UPS" is cut, and if its connected to the COM port, programmed correctly and set up in your OS right, then it should automaticaly start your 30 second shutdown with the added benefit of leaving your battery alone when the engine isn't running.

 

[blahblah99]

You can do that with some digital logic, a comparator, a transistor, and a relay connected to the power button.

 

[jasonpetras]

I would recommend using an optocoupler (also called an optoisolator) for your "relay" action. They provide high voltage isolation (usually a thousand or two volts) and easy wiring to discrete logic (as used within the power supply. Check out Digikey.com for the optocoupler. They are a really good source for "off the shelf" parts and such. As for the circuit design, wire a resistor and the diode side of the optocoupler in series to the ignition, and wire the transistor side of the optocoupler with a pull-up resistor to the ATX power input. Now, this assumes a few things, like the direction and connectivity of both the car's igition and the ATX power-on input, but the general principles will be the same. If you need a bit more info, just msg me!

 

[dzt]

use inverter (dc to ac), and then put your 12 V - 5 V cpu psu output (usually for hard drives) to relays. they will provide voltage if computer is on.
then the relay, they act as your secondary key, and your mechanic key is your primary one.
with this combination, your cpu is on at a time with your car.
you can use laptop to lower down voltage and wattagge.

anyway, use an adequate shock absorber.
a friend have computer in his car, and it become a milkshake since he use less absorber.

 

[ecopure]

Also,

For a specific car wiring color code for ignition wires go to bulldogsecurity dot com.