How would I go about monitoring my engine outputs?

[Durty-Sanchez]

Some ECU's dont work well with just the FTDI cable straight in to the OBD port, I think the tranmission lines need a pull up resistor or something, which the FTDI cables don't have. I found that early FTDI devices aren't too friendly with the strange baud rates used by the ECU if the software is using the VCP, but the newer ones are all good.

Here's the circuit that I originally used a few years back to access the OBD port. I used USB->OBD after that for a bit, but it's still limited to slow transfer rates. These days I run a subroutine within the ECU's firmware that dumps data on the system bus where it's picked up and USB'd back by another embedded system. You can log almost every channel at a ridiculously fast data rate (250Kbps), but it's still very much an experiment..

Edit: .. those pins (2,3,7) on the right are the serial cable pins. If you were to FTDI cable this I would recommend you keep the resistor/transistor setup and put it in place of the IC

[Swindog]

zzzzzzooooooooommmmmmmmmmmmmmmm ---->

right past me.

[log1call]

Sanchez,

why have you got transistors and a chip in your circuit? A simple MAx 232 chip does all that's needed. You also need an earth to the vehicle, power from the vehiclea, a five volt regulator and several capacitors. For the average Joe, that's all too complicated. The new ftdi usb to TTL cables are the way to go.

I've made and used rs232 adaptors too but these new ones need no electronic know-how at all... you just strip the wires and connect them to your diagnostic plug using a radio plug or bits of electrical tape if you want.

The leads can been seen here... http://www.ftdichip.com/Products/EvaluationKits/TTL-232R.htm

You must get the models that don't end with "-3.3" on them. They are 3.3 volt ones and won't work. The models with just "R" on the end are 5.5 volts. The simplest way to ensure you get the right one is to get out the credit card and order one from Dontronics in Australia, they have both models and won't try to fob you off with the 3.3 version.

[Durty-Sanchez]

The transistors are required on my ECU (and others of its flavour) because the ECU's line driver leaves a lot to be desired. The signal at the OBD port from the ECU is so weak that it needs to be aplified (or maybe needs pullups) as the 232 chip doesn't detect the logic levels.

AFAIK the FTDI devices also run in to the same problem (at least they did with me), so the transistors on weak signal ECU's are needed. You're right the circuit above runs off a voltage regulator driven by the OBD port, ground is provided through the OBD port too (remember to connect the serial port ground too!).

[log1call]

Hmmm. A Max chip is way more sensitive than a transistor is.

I had troubles such as you describe but in the end I discovered that too longer wires from the obd plug to the max chip was the problem. After I shortened that I could use a serial lead as long as I wanted from the laptop to the Max chip adaptor.

Perhaps your max chip was picking up interference and the transistors desensitized it so you got better readings?

The usb-ttl leads are 1.8 meters long and don't seem to have any trouble even if they are close to other wires, which can cause interferance.

Anyway.... For anyone wanting to try connecting an older SSM OBD subaru to a laptop with no electronic knowledge, the ftdi leads are the way to go these days.

[Durty-Sanchez]

The max chip maybe more sensitive than the transistors, but its flaw lies in how it detects logic transitions. The huge signal attenuation, weak line driver, and additional line noise on the OBD port all conspired for some bad connections - which the oscilloscope backed up. The semi-szalkai pair setup, when biased right, was just what was needed to get things going reliably.

Without a doubt the FTDI cables are pretty awesome, and probably the only option as com ports are a thing of the past these days! If anyone gets their cables up and running i'll try and dig out some of my older FTDI based software for reading the OBD data.

[log1call]

Hey that would be cool. What do you have? I'm always on the look-out for software because as you know, there is no one solution for OBD... not even the OBD2!

[Swindog]

Just found this.

http://www.performanceforums.com/forums/showthread.php?t=67204698

[Joker]

doesnt that lead back to this thread:

laptop cord for subarus OBD I and OBD II soulutions http://www.clubsub.org.nz/forum/index.php?topic=2853.0

[Swindog]

Sort of.

This guy makes the handheld units to be able to read them so for $250 AU you get the cable and unit.

[Swindog]

Or this then http://www.ecudatascan.com/

touch screen, gps, sd card slot

More in line with what i wanted to do.

[suubyduuby]

 Durty-Sanchez said:

Some ECU's dont work well with just the FTDI cable straight in to the OBD port, I think the tranmission lines need a pull up resistor or something, which the FTDI cables don't have. I found that early FTDI devices aren't too friendly with the strange baud rates used by the ECU if the software is using the VCP, but the newer ones are all good.

Here's the circuit that I originally used a few years back to access the OBD port. I used USB->OBD after that for a bit, but it's still limited to slow transfer rates. These days I run a subroutine within the ECU's firmware that dumps data on the system bus where it's picked up and USB'd back by another embedded system. You can log almost every channel at a ridiculously fast data rate (250Kbps), but it's still very much an experiment..

Edit: .. those pins (2,3,7) on the right are the serial cable pins. If you were to FTDI cable this I would recommend you keep the resistor/transistor setup and put it in place of the IC

Great... so the Subaru ECUs DO output serial data, but obviously at a different voltage level which needs to be translated with the line driver.

Cos I remember reading that there about 5 different OBDII protocols:

J1850 PWM

J1850 VPW

ISO9141-2

ISO14230-4

ISO15765-4/SAE J2480

I was thinking if it was a CAN interace, then you would need a micro to chew through the CAN data and spit out RS232 which you can then feed into a MAX232 or FTDI chip. If thats all there is, might lay out a PCB and test it out in the next week or so. : ;D

[nzkaosnz]

IIRC - SSM protocol is a rs232 style serial interface, except uses either ttl level or 12v (cant remember which)

[Durty-Sanchez]

The OBD & OBD2 protocol probably does need extra gadgetry, but then you don't want to be using that anyway. Sure it's standardised and you know where to look for all the sensors, but it doesn't give you access to the interesting bits of the ECU - and its slow. That circuit is to use with the SSM protocol, which is just a serial protocol over a TTL link (5v). I've got some PCB's already made for that circuit if you want the gerber files, it's designed for a com port connection though. Wouldn't be much to add a FTDI chip to it

[log1call]

The 9141 protocol is used by both obd1/ssm and the later obd2, as fitted to subaru and most other japanese vehicles.

The obd2 can be read by the same serial/usb/parrallel adaptor that you would use to read ssm.

The software is the important part. You have to know how to negotiate a connection with the car and then which bits of information to ask for.

The free software can with suitable data files be used to read obd2 or ssm.

The ftdi chip will allow for data transfer speeds well in excess of what the cars ecu can deliver.

For diagnosis and tuning work the software availiable for free is perfectly adaquate. For gauges in your car then higher speed data transfer could be a advantage, If you only want gauges then you are ignoring the real value of data logging and you might as well stick with conventional electrical gauges.

[log1call]

Dontronics... http://www.dontronics-shop.com/ftdi-usb-to-serial-ttl-level-5v-converter-cable.html $44.00 N.Z. dollars delivered to your door.

Strip the black, yellow and orange wires. Connect the black wire to the ground pin in the subaru's yellow diagnostic connector and the other two go to pins three and two. Don't worry which way, they can be swapped and tried both ways.

http://www.vwrx.com/index.php?pg=selectmonitor Free software. I can post more ecu addresses to suit this software. Or,

http://www.limitless.co.nz/ Cheap software that is leading the world and made right here in N.Z. I also have extra addresses for this software.

[suubyduuby]

 Durty-Sanchez said:

The OBD & OBD2 protocol probably does need extra gadgetry, but then you don't want to be using that anyway. Sure it's standardised and you know where to look for all the sensors, but it doesn't give you access to the interesting bits of the ECU - and its slow. That circuit is to use with the SSM protocol, which is just a serial protocol over a TTL link (5v). I've got some PCB's already made for that circuit if you want the gerber files, it's designed for a com port connection though. Wouldn't be much to add a FTDI chip to it

Do you have the original schematics/PCB layout files? (That's if there in something like Protel or something that I can import into Altium Designer)

If not all good - going to lay out a board real soon.

[Guest evolutionsti]

hey there mate,i would put in on a dyno if i were you.they work alright usually

[driftrex]

 evolutionsti said:

hey there mate,i would put in on a dyno if i were you.they work alright usually

lol you crack me up.

[cpt kernow]

saw this today and though it was pretty cool, shame it doesn't do RPM but you could rig it to injector duty, intercooler temp, speed, throttle position etc. All for $85.

http://autospeed.com/cms/A_111416/article.html

[Durty-Sanchez]

 suubyduuby']

[quote name='Durty-Sanchez said:

The OBD & OBD2 protocol probably does need extra gadgetry, but then you don't want to be using that anyway. Sure it's standardised and you know where to look for all the sensors, but it doesn't give you access to the interesting bits of the ECU - and its slow. That circuit is to use with the SSM protocol, which is just a serial protocol over a TTL link (5v). I've got some PCB's already made for that circuit if you want the gerber files, it's designed for a com port connection though. Wouldn't be much to add a FTDI chip to it

/quote]

Do you have the original schematics/PCB layout files? (That's if there in something like Protel or something that I can import into Altium Designer)

If not all good - going to lay out a board real soon.

Wasn't done in protel but exports gerber files, which you should be able to load?

[suubyduuby]

Yeah Gerber files are fine. I can import them into Protel.

What package are you using for creating your PCBs? Can also import from OrCad, PADS, P-Cad, Circuitmaker. etc

[Swindog]

Did any of you guys appear on beauty and the geek?

[suubyduuby]

 Swindog said:

Did any of you guys appear on beauty and the geek?

;D Hehe

Not a geek mate, just my work that's all.

It's a fine line that I try not to cross - but sometimes it happens... :

[Guest boostin]

Ok, so 99% of that went straight over my head.

Is there a cable I can use to connect to the OBD and OBDII ports to monitor the live data, clear fault codes etc from the USB on my laptop?