Hi gents. From my previous post, thanks to all forum members help, Here’s the schematic for OBD1 (ALDL) half duplex to USB as per the discussion.:-
However, I would like to know if the diode is actually blocking Tx signal from the USB back to OBD1 but from the previous discussion it seems to work that way.
Next is the modified schematic for using bluetooth instead of USB. From what I have read you need a resistor ladder from 5v side to get 3.3v output signal to bluetooth but for the 3.3v output from bluetooth would still be in a recognize range for a 5V TTL.
Please help me correct on this circuit as I might be wrong about it.