Bluetooth OBD-II Adapter

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.

Scantool’s module

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.

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