Reading OBD2 data without ELM327, part 2 – K-Line

K-Line is another popular OBD2 interfacing standard, that has been used in European cars before CAN bus became common. There are a couple of physical variations (K-line, K+L, KKL) and slightly different protocols (KWP2000 or Keyword Protocol, and ISO 9141) running on those lines. Basically all you need to talk to an older car is an MCU with a UART and a single transistor. 🙂
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Reading OBD2 data without ELM327, part 1 – CAN

All modern cars have an OBD2 diagnostic connector that allows reading many engine and drivetrain parameters like RPM, vehicle speed, temperatures etc.

Most of car interfaces use a special protocol translating chip like ELM327 or STN1110 to convert different vehicle protocols (that depend on the age and brand of the car) into an easier to use serial protocol with AT-commands.

I wanted to build a datalogger that would fit into a OBD2 connector. There was no space to fit my microcontroller and another chip to do protocol conversion, so I investigated and reverse-engineered the most common OBD2 protocols to be able to implement them directly on my MCU.
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