HiJackZX1
Posts: 4
Joined: Sat Jan 21, 2012 8:11 pm

Re: Questions on how RasPi works.

Sat Jan 21, 2012 8:49 pm

Hello… I have been working on a Car PC project for the past 4 years. Recently I finished the Dual Zone system, which allows the driver to do his own thing (stuff for driving) then rear (access to multimedia). This system does everything imaginable. I then had a second system which used VM to create 6 personal computers for each seat. Problem is the setup is massive and uses tons of power, and all I really need for those systems is internet, music, and video.

I had inquired on the RasPi last year, but it was not available. Thats when I installed the VM system. Now that RasPi is being sold, I can now change the setup. I do have questions and I am hoping that the RasPi community can help.

1) I know that these units use SD cards, can the SD card be read only, that way the user can not mess up anything? Also I ask because I want the main system to control the RasPi units, so it would simply shut them off when it turns off. I am not sure but on a regular system, if it is read and write, the HDD can be corrupted. Where as if it is read, it cant.

2) Would it be ok to run these units off a cigarette lighter adapter? I know the specs say that I need 5V 1amp to power the RasPi, so I assume a car charger with those specs will work. Can someone confirm?

3) My setup uses KVMP switches, which have a built in USB hub and VGA port. With that being said, all the screens use VGA ports. I see that the RasPi uses HDMI. What are my options to getting VGA capabilities on the RasPi? I see so many options on Amazon, some being simple cables and others being full adapters that need 5V power. Which do I need to use?

Any help would be appreciated.

jurian89
Posts: 4
Joined: Sat Jan 21, 2012 8:25 pm

Re: Questions on how RasPi works.

Sat Jan 21, 2012 9:10 pm

1) Most SD cards have a Lock button. I think this sets read only mode.

2) Yes, if you have a good car power adapter that can change from 12-24V DC to 5V DC it will work. I would recommend more then 1 Amp if you want to connect multiple devices to the usb port.

3) As far as i know the HDMI on the R-Pi only supports digital. You would need a active converter to convert the signal to analog VGA. Maybe the switches also support RCA video ?

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Chromatix
Posts: 430
Joined: Mon Jan 02, 2012 7:00 pm
Location: Helsinki

Re: Questions on how RasPi works.

Sat Jan 21, 2012 9:25 pm

Rather than KVMP switches, why not just apply an R-Pi to each seat?  Then you don't have to worry about multiplexing stuff - the computer is cheap and doesn't take much power.  You can still network them together with an ordinary Ethernet hub if you like.

Okay, you only get one R-Pi per shipping address to start with, which will probably delay your project...
The key to knowledge is not to rely on people to teach you it.

HiJackZX1
Posts: 4
Joined: Sat Jan 21, 2012 8:11 pm

Re: Questions on how RasPi works.

Sat Jan 21, 2012 11:09 pm

Thanx for the replies. So when the Raspi say plays video or access web content, it doesnt save to the SD card? Like If I put read only, where does the information go?

The devices that I am attaching are powered via their own power supplies.

The switches nor the screens support RCA. Plus the quality would be blurry as far as text.

The reason for the KVMP switches is because the main PC comes up on all the screens. This is how the user can interact with the PC. Then if they want to use their individual pc, they hit the proper buttons, then it switches to the Raspi and also switches the touchscreen.

Tomo2k
Posts: 127
Joined: Mon Dec 19, 2011 10:00 pm

Re: Questions on how RasPi works.

Sat Jan 21, 2012 11:37 pm

HiJackZX1 said:


Thanx for the replies. So when the Raspi say plays video or access web content, it doesnt save to the SD card? Like If I put read only, where does the information go?


"Playing" anything never requires the ability to save anything locally (eg to SD card), all the temporary cache data can stay in RAM.

The SD Card can be entirely read-only, unless the user needs to save anything (eg passwords) for next time.

HiJackZX1 said:


The reason for the KVMP switches is because the main PC comes up on all the screens. This is how the user can interact with the PC. Then if they want to use their individual pc, they hit the proper buttons, then it switches to the Raspi and also switches the touchscreen.


I'm rather confused as to why you think this would be necessary or desirable.

This concept is unnecessary and adds complexity that would make the system much harder to build and fault-find.

The RPi can send and receive any necessary commands to/from the "Main PC", easiest method being over the network.

XBMC also has multiple Ethernet (inc. WiFi) remote software systems, to allow remote devices (classically an Android or iPhone, could be another computer) to control the XBMC application.

If the "Main PC" is acting as the media server, then there are no commands a user would ever need to send direct anyway - XBMC or similar handles all the "stream me this video/audio/etc" stuff transparently.

Consider the in-seat entertainment systems on a modern commercial airliner.

These are based around one or more central content servers, plus a small "PC" in every single seat. These systems allow for "on-demand", "forced" (eg the safety video) and "overriding message" (eg fasten seatbelts) content. Including silly games!

If you replicate this kind of system, then it's trivially expandable - start with one or two seats, then you can have as many seats as you have bandwidth for by adding RPi+touchscreen sets to the network.

HiJackZX1
Posts: 4
Joined: Sat Jan 21, 2012 8:11 pm

Re: Questions on how RasPi works.

Sun Jan 22, 2012 12:16 am

The user actually interacts with the main pc. it supplies a shared environment for all the rear users. Say for example they all want to play games against each other, or all watch sat tv. Basically do highend things the raspi can not provide, etc. Basically the touchscreen is the way they all control the main pc, but its also how they control their own system. The Main PC uses a software called Centrafuse which is a infotainment software.

Tomo2k
Posts: 127
Joined: Mon Dec 19, 2011 10:00 pm

Re: Questions on how RasPi works.

Sun Jan 22, 2012 12:36 am

What shared environment?

Neither of the examples you gave have a shared environment - merely a shared data source.

Playing games against each other:

Multiplayer games are almost exclusively network-based.* While there is usually a central server the game-player never directly interacts with it, instead it holds and maintains the "game state" and passes the results of all the players actions to the game client software each player is using on their own computer (whether virtual or physical).

*The exceptions being split-screen and turn-based games.

Sat TV:

This is just streaming video. There is no direct interaction, the viewer never touches the video server.

For example, iPlayer, netflix, YouTube etc - you don't need to have a keyboard connected to the Netflix server, your PC does all that.

(I so this at home with my PVR set-top box. I can watch any recording on my PC without touching the PVR or PVR remote, even while my wife is watching anything else on the TV that's actually attached to it.)

- In the case of live TV, changing channel is a command pass back from the client to the computer that actually has the TV tuner(s). For bonus points you have two or more tuners and allow multiple channels to be streamed at once. (Digital is great as two tuners is often enough to simultaneously allow about half the possible available channels.)

Both of these are solved problems using servers with no monitor, keyboard or mouse (headless), and clients that handle all user interaction.

If you don't want the RPi clients to handle user interaction, then you don't want client computers at all. Video splitters are much cheaper.

You may have forgotten that an RPi is a fully-fledged and powerful PC.

Aside from that, even if you do need to run some user-software on the central server (eg only available as x86), use a Remote Desktop application.

HiJackZX1
Posts: 4
Joined: Sat Jan 21, 2012 8:11 pm

Re: Questions on how RasPi works.

Sun Jan 22, 2012 12:57 am

I'll get you a video demo of the system. Once you see it, you will understand.

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