OBDII Data Interception Ideas Please.

I have built a data interception device using a 12F683 for some serial data passing between two devices on an Automotive 12v OBDII K Line.

The data I need to intecept and modify comes from only one of the devices. (The Car)

The data flow is command from OBDII Scanner -----> Car Response -----> OBDII Scanner

Each device at the ends of the line has a pull up resistor and a pull down transistor so two way comms happens on one line.

I have inserted an IN4148 diode into the line so that the scanner can pull the line down and it is recd by the car, but when the car pulls the line down that is blocked by the diode.

Scanner ------ > --l<-- ---- > Car

The 12F683 listens to the cars response on the car side of the diode and modifys it then sends it to the Car using it's own pull down transistor on the scanner side of the diode.

Does inserting the diode into the line sound like a reasonable idea?

I though about using a MAX4619 to switch signals about?

Any other ideas?

Just another question the Serin2 Wait command can it wait for data in the form of hex numbers like Wait ($20,$05) or just ascii characters Wait ("AbC") ?

Hi,
Retoric question:
From the PICs point of view, what's the difference between "A", 65, $41 and %10000001

Answer:
None, they are all a representation of the same thing.

So WAITing for "A" is the exact same thing as WAITing for 65, or $41, or %10000001 and WAIT("AbC") is the exact same thing as WAIT(65, 98, 67) or WAIT($41, $62, $43).

See, to the PIC it's all just numbers it's we, the humans, who choose to represent those numbers in different ways.

/Henrik.