data logging on OBD-I cars

[techno550]

I've had a few PM's, emails, etc asking for assistance in wiring/installing/configuring various logging solutions on BMW's.

The AIM MXL is very simple to install. Somewhat ironically, the newer the car, the easier the install, as the AIM can capture via CAN. The MXL is a bit more than most want to spend though, at ~$2k+

The most common request though is centered around low cost loggers. One that I like is the labjack U3. It is a lot more budget friendly ($99), but has zero *built in* features. It has an amazingly high potential sample rate though.

The first problem most run into is what to log, and where to get that signal.

from the ECU side of things (on an OBD-I harness/ECU), you'll want:
RPM (pin 47)
Coolant temp (pin 78)
Intake air temp (pin 77)
Injector PW (pin 33)
MAF value (pin 41)
Vanos position (pin 7)
Crank signal (+ on pin 16, - on pin 43)
Cam signal (pin 17)
Vehicle speed (pin 42)
O2 (pin 13)
TPS (pin 73)
Bat voltage (pin 26)
Knock sensor 1 (pin 70)
Knock sensor 2 (pin 69)

From the chassis, it may be beneficial to source another speed input, such as an ABS sensor (or all 4 ABS sensors). The speed input on pin 42 of the ECU is the VSS in the diff, which will be skewed by wheelspin.

Knock sensors do best logging at a very high frequency and analyzing with matlab.

If using a labjack, it'll want most of the voltage inputs scaled down in the 0-2.4v range, so voltage dividers will be needed.

[97m3john]

Awesome info! were can i source the labjack?

[techno550]

Awesome info! were can i source the labjack?

www.labjack.com

[kingsiang]

any writeup? heheh... cos getting values of knock sensors by itself wont be of much use... I have used labview.. what frequencies are to be filtered?

also on voltage divider does it apply to every input?

[Robstah]

Great info Mike. The Labjack U3 seems to be where it's at for the price. Are the voltage dividers something you would find at a Radio Shack, or do you have an online site for that as well? I see the LJTick one, but how many of these do we need? 25 a piece will add up.

Also, if interested, this maybe a good idea for a groupbuy.

[techno550]

any writeup? heheh... cos getting values of knock sensors by itself wont be of much use... I have used labview.. what frequencies are to be filtered?

also on voltage divider does it apply to every input?

more to the writeup?
I suppose a chart of what the input/output looks like from the ECU would be helpful. Unless there is a specific unit identified, the "how to" will be different for each app.
Most of this is known though. RPM output from the ECU is a square wave (constant duty cycle iirc) frequency measurement. 3 pulses per revolution.
the temp sensors are theromresistors.
MAF output is voltage.
TPS is voltage.
vanos position is on/off as power/no power.
O2 is 0-1v for narrowband.
crank and cam signals would be recorded as waveform.
knock sensors would be recorded waveform as well.

Great info Mike. The Labjack U3 seems to be where it's at for the price. Are the voltage dividers something you would find at a Radio Shack, or do you have an online site for that as well? I see the LJTick one, but how many of these do we need? 25 a piece will add up.

Also, if interested, this maybe a good idea for a groupbuy.

voltage divider is easy. resistive voltage divider is just 2 resistors. 2 resistors is cheap.
build it on a protoboard, test, then breadboard it. If a handfull of people want something like this, getting a run of boards made would be easy.

[kingsiang]

thanks for the fast reply michael... but u didnt answer my question to the knock sensor.... i know its recorded as a waveform but its unuseful data... ive read somewhere that certain frequencies needed to be filtered. do you know which? also do u have one in use? if is it ok to send me the VI file?

also what u think of http://sine.ni.com/nips/cds/view/p/lang/en/nid/14604 since im still in college i can get a good price on these.

[techno550]

the national instruments stuff works fine too. there are a number of decent USB based data acquisition systems out there, and they all basically do the same thing.

for the knock sensors, the frequency depends on the motor. a specgram will make it very easy to pick out knock in post analysis.

[kingsiang]

a specgram will make it very easy to pick out knock in post analysis.
mind elaborating that a little more?

also do u have any DAQ in use?? if yes is it ok to send me the VI file?

[xjeeper]

I´d be EXTREMELY interested in buying this if you could sell them as a kit with everything I need to hook it up and instructions on how to do so. Also, some sort of guide to let me know what the voltage readings actually mean in the real world. Honestly, you would sell ALOT of them.... all of the obd1 guys have asked about something like this for a while now.

[bennyfizzle]

i'm totally down

[325icintn]

Yeah Mike, you can hire UrineMachine to build the units, since he's currently looking for a job.

Seriously though, you've got a potential winner in such a product.

[stimpee]

How about using the Innovate unit and hooking up to the appropriate pins?

5 years ago I had to spend 2K, and a lot of time, making a breakout harness and hooking up my data acquisition system to my 325 when I was developing the TS. I had to log both some of the DME data, as well as a plethora of other pressure and temperature sensors that I had added so that I could watch everything.

The options now are far better, especially with built in wideband capabilities, etc. Anyway, take a look at the innovate unit. It is relatively cheap, and has logging software, etc already set up for automotive applications...

Steve

[techno550]

innovate makes great widebands and horrible loggers. Slow sample rates, expensive for what they are, etc...

to do the above (~14 channels of logging) with an innovate package, we could do it all with aux boxes, but they are $250 for each 5 channels. From what I've seen, they also have a sample rate around 12hz. It'd be a $500-$1000 investment easily in innovate products to do the above, and it wouldn't do knock well at all.

You can suck 40,000 hz out of a labjack, which can handle 12 channels with a little room to grow.

For pre-built hardware data loggers with good configuration software, and in the affordable category, Aimsports can't be beat. The analysis software from innovate is quite weak. I found myself dumping the data out to a CSV and doing my analysis in matlab anyway.

[stimpee]

Thanks for the info. I have not used the innovate, just looked at it briefly.

I got 20hz on my system (purchased over 5 years ago), and that was adequate for what I was measuring since I could get 20hz for each channel. However I was not logging knock at the time...

[328iJunkie]

hmm. Im gonna miss my OBD2 port .

[alpinawhitem3]

innovate makes great widebands and horrible loggers. Slow sample rates, expensive for what they are, etc...

Well that sucks.

I have the SSI-4.

I am using pin 73 to log TPS.

I am using pin 41 to log MAF voltage.

My AFX will be hooked up by the end of the week to the SSI-4.

So my question is...

I am currently using pin 16 as an RPM source. Is this okay?

It worked for a previous block box that required rpm input.

[techno550]

Well that sucks.

I have the SSI-4.

I am using pin 73 to log TPS.

I am using pin 41 to log MAF voltage.

My AFX will be hooked up by the end of the week to the SSI-4.

So my question is...

I am currently using pin 16 as an RPM source. Is this okay?

It worked for a previous block box that required rpm input.

16 is the crank position sensor output. You'll be reading the 60-2 wheel. Great for analysis if you have the sample rate, but for just an RPM input, massive overkill (if it can even read it properly).
For standard RPM inputs to most loggers, external tachs, etc... the best bet is pin 47 from the ECU. goes to a black wire into the instrument cluster. (its what runs your stock tach.) its 3 pulses per rev, constant duty cycle square wave, etc...

[5mall5nail5]

16 is the crank position sensor output. You'll be reading the 60-2 wheel. Great for analysis if you have the sample rate, but for just an RPM input, massive overkill (if it can even read it properly).
For standard RPM inputs to most loggers, external tachs, etc... the best bet is pin 47 from the ECU. goes to a black wire into the instrument cluster. (its what runs your stock tach.) its 3 pulses per rev, constant duty cycle square wave, etc...

He won't be able to read the crank position sensor in terms of crank rotation speed / min. It will show you the pulse (in AC for VR, DC for Hall) as each tooth passes.

[e36'n]

Good writeup.

So the Labjack U3 can handle 12 inputs of 0-5v, which have to be scaled to 0-2.4v, but is there a program that can correlate certain channels (rpm, temps, etc.) to the actual meaningful data?

[techno550]

Good writeup.

So the Labjack U3 can handle 12 inputs of 0-5v, which have to be scaled to 0-2.4v, but is there a program that can correlate certain channels (rpm, temps, etc.) to the actual meaningful data?

The U3 is a "USB DAQ device with up to 16 12-bit analog inputs, up to 20 digital I/O, up to 2 8-bit analog outputs, up to 2 counters, and up to 2 timers."

the analog inputs it wants as a 0-2.44v. voltage resolution is 2.44/4096 so ~596uV. for something that starts as a 0-5v signal, thats still a lot of res. even on a "compressed" 12v signal that'd be a decent amount of resolution. Obviously, you build your voltage dividers based on the input voltage range.
For "digital" inputs, like vanos on an M50TU, you'd use an inline resistor to get the voltage to an acceptable range.

temps are resistance based generally.

converting the voltage or impedance to meaningful data will best be done in the acquisition software. Labjacks come with DAQFactory Express (a lite version thereof.) and that has built in conversion utilities.

[e36'n]

Thanks.

So which inputs are analog/digital out of the ones we'd want to log and what's the conversion to go from volts to rpms?

[5mall5nail5]

Thanks.

So which inputs are analog/digital out of the ones we'd want to log and what's the conversion to go from volts to rpms?

No such thing - RPM signal isn't in volts... its a pulses signal... ie PWM. For instance, it will pulse between GND and 12v or GND and 5 (the latter less commong), and so you need to write math to multiply the signal to a useable RPM or something...

[e36'n]

No such thing - RPM signal isn't in volts... its a pulses signal... ie PWM. For instance, it will pulse between GND and 12v or GND and 5 (the latter less commong), and so you need to write math to multiply the signal to a useable RPM or something...

Thanks.

So what's the formula or is it a secret?

[ReiheSechs]

You could put TRM on the map bigtime if you came up with such a product ready to go...