Well figuring out how to get useful data from your car is definitely an obscure art. Here are some notes for noobs:
- There is a standard connector for all cars after 1996 which is called OBD. (Onboard Diagnostics), you have you to google your car to figure out where the port is. But it is usually under the steering wheel (Honda Fits) or in the left change area (Mazdas) or somewhere under the dash (BMW).
- There are a huge number of OBD readers but the best ones transmit via Bluetooth or Wifi. The really neat ones use Bluetooth LE so you do not even have to pair your phone to them. There are cheap knockoffs that cost $12 on eBay, but the most reliable according to the folks at Harry's GPS Timer cost about $80-90.
- Some devices work with IOS, but many do not (there is something I haven't had time to research about the way Apple handles Bluetooth). The Kiwi 3 is really nice, it uses Bluetooth LE and just seems to work out of the box. The GoPoint BT1A uses Bluetooth as well, but you do have to pair it which is a bit of a pin. The OBLink MX is Android only and also requires pairing.
- The controllers themselves either use the ELM 372 processor or their own (GoPoint has their own). Those with the Elm will find that it is using a simple serial protocol using the venerable AT command set.
- On the actual bus there are some standard PIDs (Performance IDs) and they are in two flavors. There are problem codes indicating and internal fault and continuous codes for monitoring data in the car itself. These are called P-codes and C-codes.
- The codes themselves have a standard set, but there are also extensions per manufacturer, you have to use various sites like carobdcodes.com to figure out what they mean.
- You then buy some software for your phone that reads these values and puts up a cool display and also produces raw data in CSV form for later analysis. Our good buddies told us about Harry's Lap Timer which although somewhat arcane works pretty well. It dumps data either via email or onto a Dropbox account. It also records video from the camera's phone and can also connect to GoPros so you get that cool multiple camera view. You can even run multiple phones and have them mounted.
- You want a really good mount if you are driving. Harry's likes the RAM mount system