RS232 <-> K-line

Discussion in 'General Electronics Chat' started by jismagic, Nov 6, 2014.

  1. jismagic

    Thread Starter Member

    Sep 7, 2013
    Can any one share RS232 - K line converter schematic.
    I do see a schematic in the following link, but i see them using +12 and -12V.

    Any simple schematic you have which you can share?

  2. Papabravo


    Feb 24, 2006
    So what is the problem with using ±12V? The RS-232 spec would allow anything from ±3V to ±25V.
  3. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    From Wikipedia:
    • ISO 9141-2. This protocol has an asynchronous serial data rate of 10.4 kBaud. It is somewhat similar to RS-232; however, the signal levels are different, and communications happens on a single, bidirectional line without additional handshake signals. ISO 9141-2 is primarily used in Chrysler, European, and Asian vehicles.
      • pin 7: K-line
      • pin 15: L-line (optional)
      • UART signaling
      • K-line idles high, with a 510 ohm resistor to Vbatt
      • The active/dominant state is driven low with an open-collector driver.
      • Message length is Max 260Bytes. Data field MAX 255.
    Apparently you NEED to have +12V and -12V signals in order to comply with the single-line bidirectional protocol. I doubt the circuit shown in your link could get any simpler than that. It's really not that difficult to make a small -12V power supply, but if you want a hassle-free circuit, I suggest you use a DC-DC converter like this one.