Update: Here is the git repo
A couple of weeks ago my Dad and I were trouble shooting the cause of a check engine light on our 2000 Toyota Camry. Using an off the shelf OBD-II reader we got a warning about the EGR system. After trying every test in the book we came up empty and finally had to take it to Toyota. They found a sticky relay that was beginning to fail, which was hard to diagnose because the light would only come on after ~30Km of driving. If we had a way to monitor signals in realtime this problem might have been easier to solve. This is why my OBD-II board was created.
The board is basically the reference schematic for the STN1110, which converts many OBD-II physical layers into RS232. The bottom of the board has a bluetooth module from Deal Extreme. The plan is to connect a smartphone or tablet to the device and log data.
Similar devices exist on the market, but I couldn't find any cheap ones that have the STN1110. Scantool offers a 3.3cm x 1.5cm module for $70, but that seems a bit expensive for a $10 chip.
The STN1110 is supposedly faster than the Elm327, which is good for realtime data logging. It supports the following protocols:
- SAE J1850 PWM
- SAE J1850 VPW
- SAE J1939
- ISO 9141-2
- ISO 14230-4 (KWP 2000)
- ISO 15765-4 (CAN)
- ISO 11898 (raw CAN)
My board is 5cm x 5cm, which means the pcb can be manufactured by Seeed Studio's for $10. I'll post the schematics on git hub in the next couple of days.