![]() Reception from the K-Line is done with a simple voltage divider. This is a reference schematic taken straight from ELM327 datasheet: The physical interface is quite simple – basically you have to interface MCU’s RX and TX lines to the 12V line. Regular UARTs use 0/3,3V levels or 0/5V, while RS-232 uses +12/-12V. The “high” voltage level is actually the battery voltage (so it varies between 12V and 14,4V if the engine is running). K-line is just a fancy name for a single-wire half-duplex UART running at 10400 baud and using 0/12V voltage levels. ![]() This is a second post in series about OBD2. Basically all you need to talk to an older car is an MCU with a UART and a single transistor. ![]() 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. ![]() K-Line is another popular OBD2 interfacing standard, that has been used in European cars before CAN bus became common. ![]()
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