Building an in-car system
 

Hi all,

My parents have given me a free pass to play around with their old Saab 900 Turbo and what I'd really like to do is put a small linux computer in there as an experiment (and application, ultimately).
For this to be a realistically useful project I really should make it interface with all the cars sensors and controls e.g. speedometer, fuel gauge, mileage, thermostat et cetera. I assume that since these are analogue meters they use an electromagnetic dial? It should be possible then (and without too much effort) to hook it up to an input device like the Arduino? I don't really know because it's been a long time since I studied electronics properly. I've already found a touch screen, I'm fairly sure I know what computer I'm going to use (SheevaPlug) and I'll probably use debian with xfce for the OS.

Any thoughts would be much appreciated since this is still in the blue-sky stage.

See here:
http://hackaday.com/2010/05/18/moder...lack-security/

You will have to check the speedo, as it may be a cable. This will also run the mileometer. Have a look on the gearbox to see if there is a heavy gauge cable with a bolt fixing it in, or a wire leading from it. The fuel is a simple electronic sender unit in the tank, the temperature is from a thermistor mounted in the radiator (usually).

Make sure you filter and surge protect the power system.

Sounds like a fun. However, it will be more of an effort then you think. I'm sure you can google and find all sorts of different car projects to give you an idea of how to interface to different car systems. Do you have access to all of the maintenance manuals? You will need to investigate what type of speedometer system the car uses. If it is an old time speedometer cable you should install a separate speed sensor.

IMHO the SheevaPlug is not a good choice. I do not remember it having a video output so not sure what type of touchscreen you already picked out.

Thanks for the responses. Bottom up:

@michaelk: I know the plug doesn't have video-out but this touchscreen is USB somehow. I could also use usb graphics anyway couldn't I? The reason the plug is useful is because it is small, cheap and has very low power consumption so it can run without the engine on for quite a while. I do have the old manuals, yes. Otherwise I'll just order the Haynes manual. What would you use instead of a sheeva plug? I considered a mac mini but thought it a tad expensive.

@smoker: Thanks for the tidbit on power surge protection (I hadn't yet thought about that so a mental note is made). I hope it uses something electronic, although the car is from 1993 so probably not. Everything is analogue.

@H_TexMex_H: I don't know if this car really has anything remotely computer-like... it's from 1993.

So what is your budget?

There are USB VGA adapters and it does appear like you can install a x-server so it just might be possible. With one USB port you will need to add a hub so things might get a little messy. I assume the touchscreen interface is also USB.


This looks interesting but no actual experience and do not know how well it works or if you can get it in the UK...
http://www.mini-box.com/mini-2440-Sa...M9-Board-7-TFT

I don't really know what my budget is... under £1000 definitely. I've been looking more at the Intel ION/Atom boxes now since they are more along the lines of what may be requires (sound + video + everything else). I think that Samsung kit was a little underpowered for my needs tbh. I'm looking at PSUs on these boxes and they seem to be in the 40W-60W range. Is that acceptable do you think? I gather that car headlights are way more than 50W each so it should be fine?

Since you already have a screen, you are mostly there, cost wise. I have bought gear from mini-itx.com (not vehicle related) but they have stuff like this. Also linitx.com have a good range of mini-itx gear. Be sure to check what they send you though - I bought a mainboard and 13v mains adapter from them, and after plugging it all together found it didn't work. Eventually noticed that they had supplied a 19v adapter for a 13v mainboard. Magic smoke got let out instantly !
Got a free adapter and Atom mainboard out of them but what a waste of time. The atom mainboard was very new at the time, so Intel hadn't released linux video drivers which kind of ruined the project, so I ebayed all the gear. I was building a custom version of DSL which lived on a 16GB CF card and ran from ram. The idea was to be able to reinstall the OS just by dd-ing the image from my workstation machine. All that worked fine with a IDE CF adapter.
Maybe when I get more time (and cash) I'll have another crack at it.

PS. For power in a car you have a maximum of 10A to play with really, which gives you 120W. I would try to stay under that if possible though, unless you are going to hard wire the psu directly to the battery. You will melt the cigarette lighter adapter leads otherwise.

Thanks for the PSU info, that is really helpful. I don't actually have a screen, just a good idea of what it will probably be. I've been spending a lot of time researching different parts and found some atom/ion computers that will run off 40W which is good. That intelligent power supply thing sounds just right.

BTW automobiles (I assume true for most makes around the world) regulate between 13.5 and 14.5 (nomial being 13,8) VDC even though it is considered a "12" volt system. If your cigeratte lighter fuse is 10 amps then total wattage is 138. However, you should not exceed 80% for safety i.e. 8 amps or 110 watts.

The alternator puts out between 13.5 to 14.5 volts in order to charge the battery. You probably won't see those voltages if you measured on any wire in the main loom, for example the interior lights. But surge protection is the most important, and if you can get a regulating power supply that can handle 12 or 24 v then that's better still.
It's unlikely that any computer equipment will draw 8 Amps. Maybe a full spec desktop with lots of drives would draw near that on start up, but for the OPs purposes, he could put a 3 Amp fuse on the circuit and be ok. The cigarette lighter is 10A because it is effectively a short circuit to heat the element. Remember, being 10A capable doesn't mean it pushes 10A, only that you can draw 10A.

I found a regulating PSU that is designed for car computers at the mini-itx site so I guess that should do it.

I would disagree, my Chrysler cigeratte lighter voltage is 13.55 VDC with the engine running and 12.3 with the engine off (due to clock and interrior light on etc). I agree surge suppression is important.

Aside from the power issues, considering this is a Saab 900 Turbo (1993) does anyone have any approximate idea about how to connect to the ECU and get information from it. I've done a bit of similar stuff with a new Intel prototype (WISP) but I was given the hardware debugger already.

Any ideas (just a basic one so I can start from there)?

Here's a starting point : http://www.uksaabs.eu/UKS/viewtopic.php?f=3&t=59484