How does On-Star work?

Discussion in 'The Projects Forum' started by wannaBinventor, Nov 17, 2010.

  1. wannaBinventor

    Thread Starter Member

    Apr 8, 2010
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    I'm curious how the On-Star vehicle safety system works in terms of communication.

    Okay, so you are in a crash, sensors detect this, and the On-star rep comes in over the speaker and says "We've detected a crash, are you okay?"

    What means are they using for the communication? Cellular, satellite phone, magic? Given this means of comm, whatever it is, if your vehicle were to run off a cliff into a patch of heavy trees, would they even be able to communicate with you?

    How difficult is it to make something similar to this?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    They use cell phone for communications and GPS for location. They don't talk about the many locations where both are not available.

    They talk about wheel revolutions and direction so maybe they guess where you might be?
     
  3. wannaBinventor

    Thread Starter Member

    Apr 8, 2010
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    Thanks for the reply.

    I'd like to try a hobbiest version of this system -- maybe not for crashes, but for say my little sister driving too fast (she has more tickets/wrecks that my parents' insurance can bare). I'd like to just place a call with a recording to say my dad's cellphone saying "your daughter is driving XX MPH."

    If I'd like to incorporate some kind of crash safety system and wanted it to dial 911, what kind of (legal) issues would there be with calling 911 with a recording giving the location of the wreck?

    Let's say she was out of her home calling area. If she were in a wreck 200 miles from home, is there a way to make a phone dial the LOCAL 911? The 911 thing is just a thought, I probably wouldn't even mess with it because of the opportunity for malfunction and legal trouble.

    Still though, how hard is it to make a cellular call based on some event trigger detected with a uC? I think the GPS would just be a matter of learning the GPS module itself, but I have no idea where to start on the cellular stuff. Any idea where I could get a tutorial on that and what devices I would need to interface one to a uC?

    Thanks!
     
  4. tom66

    Senior Member

    May 9, 2009
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    It's a neat idea, but how do you make sure that your module will function in a crash? Will you still get GPS signal when the vehicle is upside down, or in a ditch?? What about cellular? Also, how do you handle the very likely problem of losing battery power in an accident? It's quite a complex thing to put together, not that I want to put a downer on the idea, but...
     
  5. wannaBinventor

    Thread Starter Member

    Apr 8, 2010
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    I think that backup battery power would be very easy to implement.

    I just think if Onstar can make it work during a crash/after a crash, I could too. I just think it's a matter of using a well protected "black box." I don't think that a rollover would affect GPS or cell communication at all.

    I think the biggest difficulty here for me is the cell phone communication. I'd think accelerometers can easily detect a crash, and it's just a matter of taking readings from it regularly and detecting a g-force spike over a certain threshold. I'd bet I could even find an acceletometer that will generate an interrupt request over a certain G force. I don't think the GPS would care which way the vehicle is oriented.

    The real trouble for me is the cell phone communication. I just don't know where to start. I think text message service would be all I needed really; it could just send a message saying "your daughter is going 84 MPH" or "crash detected @......." I know there are really two "styles" of cellular, CDMA and GSM. The problem is, I don't know where to begin there. If I had a GSM module near a CDMA tower, would it work? If I had a GSM module near a GSM tower, how does it work in terms of having it's own phone number, being allowed "access" to the tower, etc.

    I think if I could get a grasp on that, I could start trying to get something together.
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    They make a "Spy GPS" that works very well. It's around $150 or so, it is a GPS and stores about 2 days worth of movement.

    Magnet mount or screw mount to car, unmount it, bring to computer to download info to the software that comes with it. It shows addresses where car was stopped more than a minute, avg speed, max speed, and highlights any roads where the car was going over the speed limit (integrates with Google type maps with speed info).

    Friend of mine got one for his kid who is 16. Straightened out his driving "issues" in 6 months by cutting off XBox access every time he screwed up driving.

    --ETA: Verizon offers a similar service with their family plan, smartphones have accelerometers and GPS on them, and there are programs to offer the same options on the Droid, for example.
     
    Last edited: Nov 17, 2010
  7. tom66

    Senior Member

    May 9, 2009
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    Okay, what kind of backup were you thinking of?

    It probably records the last few GPS coordinates. Most GPS devices cannot keep a fix when they are not orientated towards the sky.
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    Put an additional antenna on the bottom of the vehicle.
     
  9. tom66

    Senior Member

    May 9, 2009
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    And how are you going to mux between them? You can't just tie two antennas together with high speed RF stuff.
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    OnStar flags a "crash" by deployment of airbags.

    The airbag control modules have accelerometers in them, so using an accelerometer to detect over-normal G's would be about the same thing.
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Any plans to protect her innocent victims?

    John
     
  12. wannaBinventor

    Thread Starter Member

    Apr 8, 2010
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    LOL Jpan. We are hoping there wouldn't be any innocent victims.

    And thanks for the tip on GPS orientation. I could have the uC constantly writing the GPS location and accelerometer readings to memory.

    Tom: It wouldn't have to be battery back up. I could just take the voltage in, modulate it into a square wave with a 555 with its output connected to a transistors base, run the transistor's output over a diode, and into a super-capacitor that is in parallel with the load. I'd have to do some calculating, but I think that the unit could stay on for quite a few seconds after battery power is cut -- more than enough to do some logical testing, formatting, and transmitting.

    Still stuck on the cellular stuff, so I'm open to any suggestions there.

    EDIT: Any suggestions on low cost/fairly easy to implement accelerometers and GPS modules?
     
    Last edited: Nov 18, 2010
  13. retched

    AAC Fanatic!

    Dec 5, 2009
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    I would use a sensor to determine which antenna to use based on the orientation of the vehicle ;)
     
  14. wannaBinventor

    Thread Starter Member

    Apr 8, 2010
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    Actually with a 1 second update time, which seems to be the standard minimum, I doubt I'd need a second antenna. If emergency personnel were dispatched to the immediate area (IE: last legit GPS reading), I'm sure it would be pretty evident where the vehicle was. The cellular device wouldn't care which was it was oriented. Heck, I can accidentally butt dial someone sitting in my recliner.

    I'm seeing that many GSM cell modules use an AT command set. It seems that all the commands bytes are given in ASCII. Am I thinking correctly?
     
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