OBD-2 ISO 9141-2 (14230-4, KWP2000) simple RS-232 cable

obd2 iso9141 2 cable OBD 2 ISO 9141 2 (14230 4, KWP2000) simple RS 232 cable

 

Components:

R1,2,6,7,9,10 - 560 ohm, 0.25W
R3,4,5,8 - 4K7 OHM, 0.125w
T1     - BC556 or 2N3906
T2,T3  - BC546 or 2N3904
One of our users reports that from collector of t1, r4 has to go to GND.

Tx is -12V when inactive. therefore the diagram correctly shows that r4 goes to tx because it uses the -12V to pull down Rx when RS232 is in Rx mode.

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