Carputer, car pc, woteva, I'm sourcing components...

[bboy]

i have built a similar project before.. looking to do it again.. 2nd time better, i'm interested in the touch screen and dc2dc power source!

 

[Pierre]

Why do I get the idee you ran into the same problems as me?

DC-DC will need to be something like this:

First you'll need to step up the 12V to about 30V 0 -30V, so that you will have plenty of voltage left to play with. (car batteries do get flat sometimes).

Then you'll need to step down the power to the required 12V, 5V, and 3.3V, as well as a stepped -12V, and -5V.

You'll need a soft switch setup, so you can use a small 5V relay to switch a BIG relay, to turn on power for the dc-dc coverter.

Next you'll need to have 5V for standby. That can be obtained by using a 5V regulator, connected directly to the 12V of the battery (supply).

You'll also need a way to protect yourself from a flat battery, so a simple comparitor can be used to monitor the supply voltage to the 12V output of the supply (remember the 30V? well, here is where it comes in very neatly, since that voltage will drop when the supply voltage drops ), that will give an output when the battery drops below 9.5V. that will be a constand on, so we'll need to limit that output to 1 second, otherwise the pc will just shutdown after 4-5 seconds, and not save anything.

Next we'll need a current limiting device for the 12V and the 5V, as well as the 3.3V, because we don't want to burn out the car when a problem occurs in the mainboard, or a short somewhere along the output wires (the 5Vsb, -5V, and the -12V can be fused). It will need to turn off the supply as soon as the problem do occur.

The whole supply should be fused propperly, should a problem arise within the supply itself.

Lastly, it should be small enough to fit into a regular power supply case.

Anyone up for designing such a device?

 

[JTech]

Anyone up for designing such a device?

Yeah, I can design such a device...

12V in via thick red wire from battery and black wire from car chassis

Molex connector out onto STD ATX PC mobo.

It would involve a boost converter to raise a DC rail of about 50 volts and from that I would run a textbook switched mode PSU design down to the various voltages. It would be small. May telecoms equipments I worked with long ago had this arrangement and it was compact and not too complicated in design. For a start you do not need a high voltage (robust especially against dv/dt at rated voltage = EXPENSIVE) FET switching element in your design and can get away with smaller parts. If isolation from the car is not required i.e. the ground of the computer is the same ground as the car, then things get radically more simple, I'd jack up the 12 volt rail to 24 volts with a boost converter and then derive all the rails 5V, 3.3V, and 12V with individual buck converters

 

[Pierre]

12V 0 12V, or 24V 0 24V? You'll need the negative rail for the -5, and -12V.

48V will be sufficient. If the car battery then drops to, say 10V, theoretically you'll still have 40V to step down.

It will not be to wise to isolate the supply from the car, since the audio will use the same ground, and that could cause noise.

You do need a stable supply. I don't like BSOD's, and a shaky psu will do just that.

Now remember that you'll need some amps on the 12V, and 5V, (cd rom, hdd) as well as the 3.3 (Ram, cpu, gfx). I'd say a stable 10A on the 12V rail, and about 12-15A for the 5V, and the 3.3V rail. (this is where switchmode starts to work the magic. A LOT less heat)

5V sb, -5V, and -12V can be about 1A. See, its not that simple.......

 

[captainwifi]

DC-DC will need to be something like this:

First you'll need to step up the 12V to about 30V 0 -30V, so that you will have plenty of voltage left to play with. (car batteries do get flat sometimes).
Anyone up for designing such a device?

Pierre you have this whole thing all wrong. I have the DC-DC converter here
infront of me. You stick 12volts into it and even while cranking the engine you
won't toast your mboard. It can withstand over 400v overvoltage , reverse
polarity protection and will operate with the battery down to 6v.
The DC-DC has a molex power connector that is inserted directly unto the
motherboard just like you would do with a normal AC supply.

The DC-DC powersupply switches on via a simple reset button. You don't
have to hack or engineer anything.
The 150watt DC-DC model can even drive a Pentium4, with the mini-itx
form factor you can add all the peripherals you want.

The DC-DC even protects your battery by automatically switching off if
you forgot your PC on.

Lets use our imagination a bit here. Hookup a large 12v battery, insert
a video capture card with low lux camera and catch anybody anywhere on
your farm. The moment the person walks past the infra-red camera his
image is GPRs'd to your PC in realtime.

 

[Pierre]

You see, I was taken on a trip down memory lane. The first time I tried to put a pc in my car, I was unable to find a dc to dc converter. If you got it in SA, it would make life a moer of a lot easier for all them dudes who'd like to do something simmilar! If so, I'd like say GREAT FIND!!!!!!

<edit> Btw, I'd like to see you start your car with 6V

 

[Rtaxerxes]

UPDATE:
Well, so far I have everything for my car computer BUT the screen. I got my VIA M10000, I have installed XP on the machine, got a 60GB 2.5" drive connected, and I have my sample M1-ATX power supply. I can take detailed photos of the power supply if anyone wants to try reverse engineer it. The screens are on their way, so I'm gonna be spending my weekend building a prespex cpu case. I'll put some pics up this evening.

By the way, I got a 2.5" to 3.5" IDE adaptor that wouldn't work initially. After careful scrutinising, a tiny bit of solder was joining two legs of the connector. I scraped that off, and all was well. Also, these motherboards seem to be very sensitive. I am running it off a normal ATX power supply for now, and it didn't seem to like my shiny new ram from Pinnacle. Swapped it with a stick from Rectron and it's worked wonderfully so far.

I'll put up a blog as I go along... that's if anyone's interested.

 

[bboy]

i need a touch screen.. i have a 7 inch in dash flip out at the moment which looks great.. but using a keyboard/keypad setup SUCKS

 

[Rtaxerxes]

What is the resolution on yours? And what make?

 

[bboy]

that i'd have to go check on...

 

[JTech]

12V 0 12V, or 24V 0 24V? You'll need the negative rail for the -5, and -12V

If you understood anything about SMPS design you'd know what I was intending to do. First of all the 50V rail is also regulated, it's a boost converter, it may not be all that stable and that's why, from this 50V rail we have a buck converter to derive each voltage line needed including the negative rails.

It will not be to wise to isolate the supply from the car, since the audio will use the same ground, and that could cause noise.

More proof that you haven't a clue what I am talking about

You do need a stable supply. I don't like BSOD's, and a shaky psu will do just that.

No kidding!

Now remember that you'll need some amps on the 12V, and 5V, (cd rom, hdd) as well as the 3.3 (Ram, cpu, gfx). I'd say a stable 10A on the 12V rail, and about 12-15A for the 5V, and the 3.3V rail. (this is where switchmode starts to work the magic. A LOT less heat)

With the right magnetics and proper design, easily achievable thank you very much!

 

[Rtaxerxes]

Rtaxerxes

How about you try to get stand alone psu's that will convert 12V dc straight to the required voltages. That way we won't need to use these pathetic noisy 12V to 220V inverters available on the SA markets.

I tried to build one myself. It worked, but with limited success (a bit unstable), since we only have limited parts readily available.

Sorry, I missed this. I have an M1-ATX power supply in my brother-in-laws hands, (will be in mine tomorrow) which is a 12V power supply. The reason these are cool is because it senses ignition and provides remote switch on to amps etc. So you can set different settings to tell it shutdown with 1 minute up to 30 minutes after you have switched the car off. So it does the normal ATX power supply thing as well providing some extra intelligence. Unfortunately they cost almost as much as the motherboard, but maybe an enterprising South African reverse engineer it? I'll put some close up pics on my website as soon as I get it in my hands.

Anyone got ideas on where to get a cheap GPS receiver? Either Bluetooth or USB?

Also I got my phone to use the PC as a headset last night, so the PC can definitely be a car kit.

 

[Spanky]

Yay!!

Hi guys..

i just started reading about car pcs a few days ago and cam across this thread.. great to see some interest..

The only thing that im confused about is the gps navigation..
If you buy a cheap gps reciever, where do u get SA street maps from for the navigation and how will that work?

Ive managed to find a gps off www.garmin.co.za for R3200 with SA street maps.. but thats allot. is there no cheaper way?

The power supply is also one of my concerns. if i buy a dctodc psu off mp3car.com, does it have the 5v connector aswell? or will it need some mods?

Also how will you go about the audio? would u run it from the pc straight to the amps? or would u put a pre-amp in?

Thanks guys

 

[Rtaxerxes]

GPS:
From what I've found, you can get GPS receivers as cheap as R700. Just a quick look around, I have found GPS Street Maps for around R1500. These should give you navigation as you drive, as in "turn left in 100 meters" etc. I remember reading about some programmes which take info from Google maps and use that as free source of maps.

Power: Well, I actually got my power supply, I am gonna start building the perspex PC case tonight. The power supply I am using looks after everything. You put 12v, switched 12V (ignition monitoring) and 0V in and it puts out and ATX connector and a hard drive power connecter. All done for you, it even monitors your battery and switches off at 11V, will automatically switch your amp on after the PC so you don't get a thump and put your PC into hibernate mode.

Screen: They have left. I'll let you know when they land...

 

[Pierre]

If you understood anything about SMPS design you'd know what I was intending to do. First of all the 50V rail is also regulated, it's a boost converter, it may not be all that stable and that's why, from this 50V rail we have a buck converter to derive each voltage line needed including the negative rails.

I'm not a complete noob at smps's. I do know that you need a pwm (I tried it with a tl 494, since I saw that it is mostly used) to switch some mosfet. (I used some irfz 44 n's). I used the transformer from a blown amp I had at home.

The effect was pleasing, but not something to send letters to your mom about. I could not figure out how to get more amps out of the secondary side.

I did read about buck converters, and crowbar protection, and some more stuff.

My knowledge about smps's can only get me as far as to what the internet allowed me to learn, so have you got some propper links on that subject? If you do, please share so I can learn some more.........

More proof that you haven't a clue what I am talking about

There will always be someone who knows better than you, and I have learned that you just need to throw something in a pot, and start stirring, and someone will take over. Then all you have to do is sit back, and start to learn, so please continue. I will be your student till the the mind gets fed up......


Now where can I get some more info on that buck converters?


<edit> don't mind about the links. I found something. Thanks.

<edit> Great! general knowledge of smps no includes basic understanding of step down/ step up buck converters, as well as basic understanding of crowbar protection. I still need to find out how you will be able to get a negative voltage on a positive rail though.......

 

[Rtaxerxes]

Got the screens!

The screens for my Car PC arrived yesterday. So I have 2 spare 7" Lilliput LCD touchscreens available... 1 is sitting in my car and is working great. Sorry for the delay on putting up pics, but I been spending my time setting the thing up, and not putting the pics on my site.

I will do it though, one of these days...

 

[Obelix]

how much for a screen? im in london right now, but might not be able to get one while here..

 

[Rtaxerxes]

R2500. Brand new in box, unopened. Comes with a stand to mount to a dashboard or whatever and a remote and all the cables and drivers you need. Has VGA input and Composite (RCA) and sound and built in speaker and is touchsreen with a stylus. Very Cool!

I just put mine in and would have pics up but not 100% up-to-scratch with Mambo on my website. But I persevere...

 

[bboy]

get pics boy!

 

[bdt]

This is a bit of a fluff piece, but it may be useful for some/more ideas than the basics, has some good links too (at the bottom).