I've got something that is probably going to be really simple for the elecronics people here. I'm setting up a PC to run in the car. It will be running Vista with Media Center for the interface, which is actually really easy to use while driving.

What I'm needing, is something that detects 12v current on a wire, and when that happens, connects 2 other wires for only a second. Basicly, when the ignition makes the 12v wire hot, I need it to press the power button to wake the PC from suspend.

I'm sure that would be really easy to do, any ideas?

Why not just wire your own power button up in the front console or something? It'd be easier, and you could suspend the computer whenever you wanted. Plus you wouldn't have any oddities like when you have to use the ignition multiple times to get the car going, or whatever.

sounds like a job for a d-flipflop.


...are you turning this off manually by the way? because it does take time for a computer to go into suspend mode. if you cut power instantly you'd destroy that computer so fast it wouldn't be funny.

No the computer will always have power to it. This is just going to detect 12v coming from the ignition switch, and press the power button. That way the startup time will be almost instant, and it will pick up where I left off.



I'm going to have a button up front as well, for those weird times, but most of the time I want it to be automated. Also, the times when I have to crank more then one time won't matter, because the ACC wire has 12v unless I take the key all the way out.

First of all, you'll want your PC's power supply to be a DC-DC type, so that you can run it straight from the battery instead off of an inverter. Lots more efficient. The picoPSU is an example of a very small DC-DC power supply.

Like Jon`C said, probably a d-type flipflop. I'll look more into that later, I've gotta go visit housing on campus about my apartment soon.

Basically, you would set up Vista (or, even better, your BIOS) so that the power button always acts as suspend. Assuming that you have a modern motherboard that supports the S3 level of suspend, you can save a lot of power. This is where everything but the RAM is powered off. Fans, hard drives, CPU, everything else. The RAM is running completely off the 5v standby rail on the power supply. With a DC-DC PSU, you can waste very little of your car battery to keep it running.

Getting a DC-DC power supply is key here. Going from battery -> inverter -> power supply -> PC would be a huge waste for keeping it in suspend. Not to mention you can save gas with a DC-DC supply too!

I'd expect leaving it suspended all the time would be needless waste of battery. I don't know how significant a constant 5v drain is, but it certainly can't prolong battery life.

I can't seem to find much on google about how much current the S3 standby state draws. The best I can find is somewhere between 50 and 100mA. I'm not sure if this is measured directly on the 5v SB rail (probably) or at the wall. Using a high-efficiency DC-DC power supply, the load on the car battery should be very minimal.

You could also probably do it with a non-latching relay.

Isn't a latching relay one that physically latches in place, as to not require constant current to maintain the connection?

Yes.

In this case, a non-latching relay would return to its normally closed position, which would cut off current flow to the power switch circuit as soon as the current from the 12v wire was cut off.

Of course, the relay would continue to be in its normally open position until the current is cut off, which may not be ideal if you want almost instantaneous switching.

A constant 12v to the computer's power switch could also probably damage the computer. You need something that will open again as soon as it engages. I'm sure there are relays that do that. Don't limit yourself to radioshack, check autoparts stores too.

You might even be able to do this with a single transistor.

Been to [url]www.mp3car.com[/url] yet? They might have some info too.

Yeah but a PC needs a momentary switch to turn it on and off again. What you're suggesting is basically pressing and holding the power button to turn it on, then letting go an hour later to turn it off. It won't work.

Isuwen, there wouldn't be 12v applied to any power leads. All you do is switch them together.

In any case you'll need a flipflop.

Would it be possible to get internet connectivity while you're out driving around?

if you are either very rich or very dishonest, yes.

Why in the f***ing hell would you want a f***ing personal computer in your f***ing car, you f***ing nerd?

You don't have to be rich... You just need to be a Sprint or Verizon subscriber, and get an EVDO RevA PCMCIA adapter for the system. It'd be cheap, and the data plans are pretty reasonable... About $50 a month for unlimited access. It's 1mbps / 600kbps average connection rate.

Yeah, they're quite swank and very reasonably priced. Only issue is if you're driving out in the boonies a lot.

Actually, as I understood it, the 12V would be hot as the starter circuit is being used, ie, when the ignition is activated. It'd be like holding the power switch for 1-2 seconds during initial ignition. Of course, this may still not be what you want.

Nah, Sprint EVDO card in a Linksys 3G Wifi Router, running ethernet up to the mac mini which is going to be in the glove box. zenarc 7 inch touchscreen going up front, and the sound running into a pioneer bluetooth head unit that will mute the sound when a phone call comes in and let me take the call over the car speakers.

thanks for the ideas everyone, keep em coming!

Well, this does bring up a point.

because i'm a ****ing nerd, apparently. also because i have lots of music, and this is the best way i've found to make it all easy to get to while in the car.

and most importantly, because it's what i want to do. i'll enjoy setting it up, and i'll enjoy using it when it's done. seems like pretty good reasons...

Or get ClearWire? yeah, that depends upon your location, but its a lot cheaper, and its mobile broadband internet.

Well, at least that is settled.

Those Cingular aircards don't cost too much.

But I have no idea how you're going to use one on a desktop in a car.

You could try to use a D Flip-flop. Start by adding a voltage divider to bring the 12v ignition (actually about 13.1 in most cars) down to 5 volt signaling or whatever the Flip-flip is rated for.

But I don’t know if that will work. I skimmed the ATX, standard, and there really is not mutch about the front pannel connections, that seems to be more of a convention than a standard. My worry is the currents involved. Flip-flops and other TTL digital logic components usually are not too happy with current flowing through them. Datasheets for common Flips-flops usually put their operating currents down in the micro-amps. That said, the PS_ON# line is specifically designed to be TTL compatible...

You could probably do this with just a single Enhancement Mode Transistor and a voltage divider (two resistors), but it would take a bit of either luck or work to figure out exactly the tolerances you would need, especially not knowing how the Front panel switch works. I'll see if I can look into this more later.


Finally. To answer Rob’s question, one of these might work for the PCMCIA wireless cards.

The problem is if the car doesn't start the first try. The next attempt will shut if off again.

Oh! You could use a capacitor and a simple timer IC. The capacitor would charge until the timer disconnects it, at which point it discharges into a transistor or relay, providing a momentary connection for the power switch.

Now, how to turn it off...you could have a capacitor that keeps a charge while the car is on, and once it turns off, the capacitors empty into a relay or transistor that momentarily connects the power switch.

Maybe I'll throw together a circuit diagram tomorrow for you. Or at least elaborate a bit more. It's getting late.

Ok, so I really can't seem to find any documentation for the front panel power switch. The best I can find seem to be the “Front Panel I/O Connectivity Design Guide” by Intel. In it they describe a simple Pull Up resistor configuration, with either a 2.2 kΩ running off the 3.3v standby line, or a 10 kΩ off the 5v standby line. Ohm’s law states that we are looking at either .5mA or 1.5mA current through your momentary switch, which is significantly higher than the μA rating of most D Flip-Flops.

One of us should probably just hook up a ammeter to a motherboards power switch and see what currents we are looking at in reality.

In a PC you short /PS_ON to ground to turn on computer, disconnect from ground to turn it off. You do not want any current to be involved at all ever.

If you're using the motherboard pinouts what they do is close the circuit to indicate the power button is being pressed. The front power switch is actually a software switch and the computer can behave differently depending on how long it is pressed.

If this is a Mac Mini it changes the situation somewhat. It doesn't have either of these things. Fortunately they do support wake-on-USB so that might be something to investigate. Honestly, though, your best option might be to have it wake up if you touch the screen.

Exactly how much music do you have? I understand that you want to put a PC in your car, but surely there's an mp3 player out there that'll hold your music.

Get a PSP and mount it to your dash :p

Have you been there yet? I'm sure you can get this question answered in less than one post on their forum.

Not really, it was ignorant. A car PC is the best way to integrate DVD, MP3s, navigation, and access to your vehicle's onboard electronics. Among other things. When done properly the install looks completely stock. If you think about it, many manufacturers already put stripped down computers in the dash. The car PC simply improves upon the design.

It's stupid. Does he live in his car? Does he have a bunch of screaming brats? He doesn't need any of those things. No one needs to access their onboard electronics while driving (except perhaps a turbocharger, but there are much simpler and cheaper means of doing that). Also, they have this funny feature now, "iPod integration." Apparently, it can handle MP3 stuff pretty well. Navigation? WookieWookie.

I think it would be kinda cool to have it simply all connected, and you could have
masses more media on a PC than say an ipod or psp. Could do it here in the UK though, they have a big enough problem with phones, can you imagine altering your playlist, or if VISTA crashed whilst your driving

PS_ON# is designed to be TTL compatible, so yes, by nature the currents involved in it are near zero. This is one of the many reasons why it's relatively safe and fun to start a Power Supply by sticking a bent paper clip between the green (PS_ON#) line and any black (ground) lines on the Main power connector.

I was talking about the Front Panel Switch, which as you indicated is a "software" switch (Its probably just ACPI, which explains why its so hard to get Linux to recognize pressing the power switch). Unfortunately that switch is the one with currents in it.

If you wanted to drop TTL Logic components (like a flip flop) on the PS_ON# line, you would have no problems, but if you wanted to use the front panel switch TTL is out of the question. This has both some good and some bad consequences. PS_ON# is NOT a momentary line, to turn on a Power Supply you need to hold PS_ON# at logical low. So we don’t want a D Flip-Flop. This does mean however, that he could just use a Relay or even just a NOT gate or something so that as long as the 12 (13.1) Volt Accessory line is hot then PS_ON# would be “ON”. This solves the problems associated with starting the car quite nicely, and also makes sure that when the car is turned off, the computer goes off with it. Unfortunately some Motherboards may not be happy with you bypassing the PS_ON# line like that, and you would certainly loose the ability to shut down the computer through software, but that seems like a fair trade off.

The alternative is still trying something like a transistor on the actual Motherboard Power Switch, which needless to say will be a bit more complicated, and to be honest, I really can’t think of any good reason to use it…

Now for Mac Mini specific stuff... I got no idea.

Bah, you're right. I forgot about that.

Hey, if you prefer to use limited technology in your car, fine, but don't act like it's dumb for somebody to prefer a safer and better interface in theirs.

i f**king love you.