OBD MPGuino gauge - Page 35 - Fuel Economy, Hypermiling, EcoModding News and Forum

Rando · 04-06-2009, 11:38 PM

Hi everyone,

Firstly I want to thank DCB and Magister and the rest of the developers for what promises to be a cool gadget. I built and OBDuino last weekend based on the Arduino Duemilanove for a 1999 Toyota Tacoma using the MC33290 and an ISO interface. Unfortunately I have not been able to get the Arduino to talk to the car. Much like Mothinator I get to the ISO9141 Init stage and it always fails. I have scoped the K-line and I see the initialization bytes going out the first time, but nothing else. The init does not send anything out on subsequent attempts. I cannot really tell if anything is coming back in as I can't really capture the bytes on my oscillioscope. Mothinator, did you ever find a solution? Does anyone else have ideas in things to try?

dcb · 04-07-2009, 12:07 AM

maybe a stupid question, but what pins have connections on the obd connector in the car? I can't see anything online that says if a 99 tacoma is VPW or ISO. 97 is vpw, 2000 is ISO, and didn't see anything about the years inbetween.

Rando · 04-07-2009, 12:28 AM

Not a stupid question at all. When I first built the OBDuino I just assumed it was ISO9141, I didn't actually check until it didn't work! Anyway, the two grounds the K line and the batt are the only pins populated in the connector under the dash. When I scope the K-line with the car off it hovers at 5V, when the car is 'on' or the engine is running I see 12v on the K -line. When I plug in the obduino I see s a few slow (~5Hz) bits go by followed by some faster bits, then nothing. This makes me think that the wiring etc is correct (I have checked it twice) and that at least the transmit function of the MC33290 is working.

dcb · 04-07-2009, 12:56 AM

I might see if a neighbor with a late 90s asian car will let you try it in their car.

P.S. Welcome to Ecomodder

Rando · 04-07-2009, 10:38 AM

I will see if anyone at work will let me plug this strange look contraption of wires into their vehicle! Another thing I need to to check is the MC33290 RX -> arduino line to see if anything appears on this. Does anyone know if this is supposed to idle high or low?

Quote:

Originally Posted by dcb

I might see if a neighbor with a late 90s asian car will let you try it in their car.

P.S. Welcome to Ecomodder

Froggy · 04-09-2009, 05:14 PM

The OBDuino looks like a fun little add on for the car. Apparently the Toyota Matrix (my car) uses both ISO9141 and CAN protocols (I don't know for sure though). I don't know which interface to build. Any suggestions? Will there be any operational difference between the choices?

I was thinking of getting the ScanGuage, but the OBDuino will be more fun to make and program.

Magister · 04-09-2009, 05:30 PM

ISO run at 10400 baud while CAN run at 500k baud, so the update is faster with CAN.
What year is your matrix?

Froggy · 04-09-2009, 08:13 PM

I suppose I will go for the CAN interface (I like larger baud rates!)

It's a 2006 Matrix in the base trim.

Froggy · 04-15-2009, 05:58 PM

I notice in the code for OBDuino that the ELM and ISO interfaces are supported, but I don't see support for CAN. Is there actually support for the CAN interface in the code, or does this still need to be added?

Magister · 04-16-2009, 10:06 AM

ELM supports all protocol so even if your car is PWM or VPW, building the correct hardware part around the ELM327 will make it works.

I am working on a CAN only PCB à la MPGuino, a small board with all the chip on it, buttons, LCD.