The interface isn't a problem. It's a 4 pin low speed data xfer, and usb adapters are already available. The issue would be getting the specs on the data that's sent by various cars.
Example - I could test on a Lexus and probably grab the data and figure it out. That won't help for a Ford. I'm sure there's a resource out there that tell the various data sent by each manufacturer, or else there wouldn't be 45 dollar laptop solutions.
The auto industry is one I'm pretty damn familiar with. I already provide some services to Mile One Corp and Group 1 Automotive (shameless plug )for data hosting, as well as call center operations. I know someone who may be interested in this, I just finished working with him on an iPhone solution for auto starting and unlocking automobiles. I'm meeting with him Tuesday, and I'll see what he has to say.
In the meantime, I suggest you write a little proposal for your idea and email it to yourself. This shows the date and time in case there are any "issues" when/if a solution like this comes to market. This wouldn't be a .99 app, so there may be potential for some serious profit, and you deserve your share for thinking of it.
To update on this. The project sounds very interesting, and we hashed around a bunch of ideas how one would go about getting it started. Then a stumbling block hit.
This would likely be as battery intensive as a voice call. Since the mini USB would be in use to collect the data, is the app still useful if
A - it can only be used for a limited time while you're driving
B - Will a consumer accept the fact that using this may very well eat the battery enough that the radio will no longer function.
In my/our/his opinion, this is a very interesting idea for an application, and once the power supply factor was worked out would likely appeal to men 18-25 (who also happen to be the Android target audience). Solutions could be manufactured that allow direct connection to the phones power supply, such as a new battery cover with a charging port attached directly connected to the battery contacts, but it's likely beyond the scope of a small development team.
He suggested you present your idea to Pertronix or another high preformance auto electronics maker. Stress the point of the Droid's industrial look and feel, and point out the appeal the device would have to tuners and other folks who like to tinker, as they are likely to have cutting edge electronic devices anyway. Use the Droid as your selling point, and not the Hero or Eris
You've got a good idea in your hands. I wouldn't give up on it. If you ever get to the manufacturing and testing phase, I'd love to try it on my LX, I don't believe that 18 mpg rating
Instead of a USB adapter, could a battery-powered bluetooth adapter be used? Then, have the obdii communicate to the phone app via bluetooth so that the phone can still receive the data without so much power being used, and the phone can sit on a charger within the car.
Power wouldn't be too much of an issue. On the OBD-II connector, pin 16 is 12v power and pins 4 & 5 are both ground.
Generic OBD-II would be accessible since it only uses 1 serial data line (I believe). You would be able to access P0xxx codes and their definitions since they are the same on all cars made since 1996. example P0302: Misfire on cylinder #2. Also, live data is available through generic OBD-II, but not as functional as manufacture specific data.
Manufacture specific codes, P1xxx format, would pose a problem since it uses multiple serial data lines. The device would have to be formatted to know which pins to pull information from for that specific make and model.
P1xxx codes would be readable in generic OBD-II, however their definition is not the same for every year, make, and model. You would need a rather LARGE database to be able to pull those definitions.
The Bluetooth device is a good idea, but I'd expect it to be rather pricey. Honestly, if you want this functionality, you'd probably be better off with an inexpensive code reader from your auto parts store.
I'd love to see gauges on the face of the droid with configurable ODB-II parameters like my Batt volts, coolant temps, oil pressure, etc .. I know there are gauges by PLX that do this now .. but an app for Android would be awesome! You could use the car mount and have a couple of configurable gauges!
I have an SCT XCal-2 that has an ODB-II port to USB connector so I can hook my laptop up to the car and data log all of the ODB parameters (thru the device) and show them graphically. This thing was more like $400 though .. and it stores/loads custom ECU tunes for the car as well.
Buy a bluetooth ODBII adapter from ebay (~$40), download a terminal application that supports serial connections pair your phone to the ODBII adapter, launch the terminal app & connect to the BT serial port....done.